Diversity and Life History Traits of Native Weed Communities in Agricultural Areas: A Case Study in Eastern China

Abstract

Native weeds have a long history of adaptation to local environments. Understanding the relationship between the occurrence of native weeds and their life history traits is crucial for effective weed management and risk assessment of plant invasions. In this study, we surveyed native weed species and their dominance across 666 field sites in agricultural areas of Yangzhou City, China, and each site was 13.3 hectares in area. A total of 287 native weed species were recorded, referring to 63 families, among which 45% were 50–100 cm in plant height and 47% were of an erect life type. In terms of the proportions out of the total native weed occurrence dominance, Poaceae, Compositae, and Fabaceae weeds accounted for 30%, 13%, and 11%; liana and perennials both occupied 32%; and aquatic, hygrophyte, sun plant, and shade plant all occupied < 10%. Additionally, the proportions increased with increasing seed production per plant and with increasing weediness reported worldwide. Native weed groups holding moderate vegetative reproduction abilities, moderate seed sizes, or herbicide resistance showed higher proportions. Moreover, most of the native weeds surveyed were not succulent or thorny plants and did not hold thorns, awns, obvious hairs, or mucilage on their fruits.

Full text

Citation: Chen, G.; Huang, Z.; An, K.;
Chen, Y.; Xue, J. Diversity and Life
History Traits of Native Weed
Communities in Agricultural Areas: A
Case Study in Eastern China. Biology
2024,13, 704. https://doi.org/
10.3390/biology13090704
Academic Editor: Robert Henry
Received: 28 July 2024
Revised: 3 September 2024
Accepted: 5 September 2024
Published: 7 September 2024
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
biology
Article
Diversity and Life History Traits of Native Weed Communities in
Agricultural Areas: A Case Study in Eastern China
Guoqi Chen *, Zeyue Huang, Kai An, Yang Chen and Jiahao Xue
Jiangsu Key Laboratory of Crop Genetics and Physiology/Jiangsu Key Laboratory of Crop Cultivation and
Physiology, Agricultural College/Research Institute of Rice Industrial Engineering Technology of Yangzhou
University, Jiangsu Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou
University, Yangzhou 225009, China; hh1003741822@163.com (Z.H.); 16638727457@163.com (K.A.);
yzuchenyang@163.com (Y.C.); 18205251761@163.com (J.X.)
*Correspondence: chenguoqi@yzu.edu.cn
Simple Summary: Plant invasion represents a significant global ecological challenge, and effective
management of invasive species requires robust weed risk assessment systems. These systems pre-
dominantly rely on understanding the relationships between life history traits and weed occurrence.
In this study, we conducted a survey of native weed communities across 666 field sites in agricultural
areas of Yangzhou City, China, covering a longitudinal range of 0.86
◦
, a latitudinal range of 0.84
◦
,
and an altitude below 100 m. Our findings reveal that dominant weed species are concentrated
within a few families and are associated with higher levels of weediness globally. The key traits of
prevalent native weeds include moderate plant height, absence of thorns, non-succulent, erect growth
forms or lianas, and adaptability to a range of light conditions, whether mesophytic or xerophytic.
Dominant native weeds were frequently annuals, biennials, or perennials with moderate vegetative
reproduction abilities and high fertility, possessing seeds of moderate size and fruits without mu-
cilage, conspicuous hairs, thorns, or awns. Additionally, many have developed herbicide resistance.
This study is the first to focus on the diversity and life history traits of native weed communities in
China, providing valuable insights for refining weed risk assessment and management strategies.
Abstract: Native weeds have a long history of adaptation to local environments. Understanding the
relationship between the occurrence of native weeds and their life history traits is crucial for effective
weed management and risk assessment of plant invasions. In this study, we surveyed native weed
species and their dominance across 666 field sites in agricultural areas of Yangzhou City, China, and
each site was 13.3 hectares in area. A total of 287 native weed species were recorded, referring to
63 families, among which 45% were 50–100 cm in plant height and 47% were of an erect life type. In
terms of the proportions out of the total native weed occurrence dominance, Poaceae, Compositae,
and Fabaceae weeds accounted for 30%, 13%, and 11%; liana and perennials both occupied 32%; and
aquatic, hygrophyte, sun plant, and shade plant all occupied < 10%. Additionally, the proportions
increased with increasing seed production per plant and with increasing weediness reported world-
wide. Native weed groups holding moderate vegetative reproduction abilities, moderate seed sizes,
or herbicide resistance showed higher proportions. Moreover, most of the native weeds surveyed
were not succulent or thorny plants and did not hold thorns, awns, obvious hairs, or mucilage on
their fruits.
Keywords: family; field survey; herbicide resistance; life history trait; occurrence dominance; species
richness; weediness
1. Introduction
Weeds refer to plants with populations that are all or mainly grown in environments
disturbed by humans [
1
]. Among crops, the total global loss due to weeds varied from 7.5%
Biology 2024,13, 704. https://doi.org/10.3390/biology13090704 https://www.mdpi.com/journal/biology

Biology 2024,13, 704 2 of 17
to 10.5% [
2
]. Weeding is essential for human society to engage in agricultural production,
landscape maintenance, biodiversity conservation, and other activities. On the other hand,
as a part of biodiversity, weeds are also important resource plants [
3
]. Many weed species
have a series of values, such as medicinal, feeding, edible, ornamental, and breeding
resources. Therefore, weediness has been proposed to distinguish the ability or potential
of different types of weeds to cause damage to human society. Moreover, understanding
how weed communities assemble as a function of biotic and abiotic filters and transform
through time has important implications for the sustainable management of agronomic
systems [
4
]. Therefore, field surveys on weed communities are one of the basic works in
weed sciences.
Research processes in weediness are also commonly used in the risk assessment of
alien invasive plants to guide the introduction of plants [
5
]. For example, the Australian
Weed Risk Assessment System (AWRA) is an effective pre-border screening weed tool that
is widely used around the world [
6
]. This system divides the risk of plant species based on
responses to 49 questions, such as species biology and biogeography [
7
,
8
]. The American
Weed Risk Assessment System (USWRA) was developed using a logistic regression model
based on the Australian WRA [
9
]. In Europe, Weber and Gut (2004) developed a Europe-
specific weed risk assessment system (WG-WRA) using a quantitative grading system
similar to AWRA [
10
,
11
]. These risk assessment systems usually assign values based on a
series of crucial traits of specific plants and finally obtain a numerical risk coefficient, which
is used to determine the risk of invasion. Therefore, having knowledge of the corresponding
relationship between a series of traits and weediness is important for weed management
and risk assessment of plant invasions.
Baker [
12
] first studied the related traits of weediness in 1965 by comparing weeds and
non-weeds; he discussed the factors that make a species become weeds and defined the
concept of ‘ideal‘ weeds. Many researchers have studied weed-related indicators [
13
,
14
],
with numerous studies focusing on comparisons between exotic and native weeds [
15
].
Systematic analysis based on native weed communities may also yield important results.
Native weeds have experienced a long history of adaptation in the local areas and have
a long-term interaction and adaptation to the local environments. Distributions of native
weeds are generally closely related to their adaptive characteristics [
16
]. Therefore, having
knowledge of the relationships between the occurrence of native weeds and their life history
traits could be important for weed management and risk assessment of plant invasions.
We conducted systematic field surveys on native weed communities in agricultural
areas in Yangzhou City, Jiangsu Province, China, from 2022 to 2023. A total of 666 field
sites were randomly selected, and each site was 13.3 ha. in area. We investigated the native
weed species and their relative dominance, respectively, in each site. As a case study based
on field survey data on native weed occurrence, this study aimed to reveal the important
life history traits relating to weediness in agricultural areas.
2. Materials and Methods
2.1. Investigating Area
Yangzhou City (119.027–119.897
◦
E, 32.232–33.397
◦
N) is located in Jiangsu Province,
China, with an altitude range of 0–81.71 m and an area of 6591.21 km
2
. Yangzhou City has
a subtropical monsoon humid climate and an average annual temperature of 16.1
◦
C [
17
].
The main crops are rice, wheat, oilseed rape, vegetables, and various plantations.
2.2. Investigation Method
From September 2022 to July 2023, 666 random survey sites were set up in the agricul-
tural planting areas in Yangzhou City (Figure 1). Each site surveyed an area of 3.4 hectares,
which contained at least two different habitats, such as arable lands, irrigation canals and
ditches, plantations, roads, or ponds. Field surveys were conducted during the lush growth
period of weed communities in September and October 2022 and April, May, June, and July
2023. Each year, we drove around agricultural areas and selected sites randomly, and the

Biology 2024,13, 704 3 of 17
interval between two adjacent sites was >3 km. At each site, the species of native weeds
were recorded, and the occurrence dominance was estimated using a visual scoring method
(Table 1), which was frequently used in weed community field surveys in China [18,19].
Biology 2024, 13, x FOR PEER REVIEW 3 of 18
hectares, which contained at least two different habitats, such as arable lands, irrigation
canals and ditches, plantations, roads, or ponds. Field surveys were conducted during the
lush growth period of weed communities in September and October 2022 and April, May,
June, and July 2023. Each year, we drove around agricultural areas and selected sites ran-
domly, and the interval between two adjacent sites was >3 km. At each site, the species of
native weeds were recorded, and the occurrence dominance was estimated using a visual
scoring method (Table 1), which was frequently used in weed community field surveys in
China [18,19].
Figure 1. Distribution map of sites.
Table 1. Visual scoring method for weed dominance value in crop fields.
Code Maximum Height of Weeds in the Field
>80 cm a 20 cm–80 cm b <20 cm
c
0.1 1–3 stems or total coverage <0.1% <10 stems or total coverage <1% <15 stems or total coverage <2%
0.5 4–10 stems or total coverage 0.2–0.9% 11–15 stems or total coverage 1–2% 16–30 stems or total coverage 3–5%
1 11–15 stems or total coverage 1–2% 16–30 stems or total coverage 3–5% 31–60 stems or total coverage 6–10%
Figure 1. Distribution map of sites.
Table 1. Visual scoring method for weed dominance value in crop fields.
Code Maximum Height of Weeds in the Field
>80 cm a20 cm–80 cm b<20 cm c
0.1 1–3 stems or total coverage <0.1% <10 stems or total coverage <1% <15 stems or total coverage <2%
0.5 4–10 stems or total coverage 0.2–0.9% 11–15 stems or total coverage 1–2% 16–30 stems or total coverage 3–5%
1 11–15 stems or total coverage 1–2% 16–30 stems or total coverage 3–5% 31–60 stems or total coverage 6–10%
2 16–30 stems or total coverage 3–5% 31–60 stems or total coverage 6–10% 61–100 stems or total coverage 11–25%
3 31–60 stems or total coverage 6–10% 61–100 stems or total coverage 11–25% 101–200 stems or total coverage 25–50%
4 61–100 stems or total coverage 11–25% 101–200 stems or total coverage 25–50% 201–500 stems or total coverage 50–90%
5 >100 stems or total coverage >25% >200 stems or total coverage >50% >500 stems or total coverage >90%
a: Near or above the crop. b: In the middle of the crop canopy. c: At lower heights within the crop.

Biology 2024,13, 704 4 of 17
2.3. Traits of Weeds
We listed the life history traits of weeds studied here by referring to the Australian
Weed Risk Assessment System (AWRA) [
8
] and the Agricultural Weed Assessment Calcula-
tor (AWAC) [
20
], as well as references on weed risk assessment conducted in China [
5
,
6
,
21
].
A total of 13 indicators were listed (Table 2), and each indicator was divided into two to
four sorts of traits. The specific characteristics of each plant species and the categories to
which they belong were determined mainly through field observations and by consulting
the Flora of China website (https://www.iplant.cn/)(accessed on 5 May 2024).
Table 2. Weed trait indicators.
Code Indicator Traits
1 Plant height >100 cm (tall), 50–100 cm (moderate), or <50 cm (low)
2 Life type Rosette, erect, creeping, or liana
3 Thorns or hooks Yes or no
4 Succulent Yes or no
5 Drought resistance Aquatic, hygrophyte, mesophyte, or xerophyte
6 Shade tolerance Shade plant, moderate, sun plant
7 Life span Annual or biennial or perennial
8 Seed production per plant
<200 (low fertility), 200–2000 (moderate fertility),
2000–20,000 (high fertility),
or >20,000 (very high fertility)
9 Size (mm)
Diameter or length < 2 (tiny), 2–4 in diameter or 2–6 in
length (moderate), or
diameter > 4 or length > 6 (big)
10 Vegetative reproduction No, moderate, or strong
11 Appendages of fruits Mucilage, obvious hairs, thorns or awns, or none of
the above
12 Herbicide resistance aYes or no
13 Weediness bUnclear, common, principal, or serious
a
: According to HRAC (weedscience.org/Home.aspx) (accessed on 20 May 2024) researching reports in Web of
Science (webofscience.clarivate.cn/wos/alldb/basic-search) (accessed on 20 May 2024), and CNKI (www.cnki.
net/) (accessed on 20 May 2024). b: According to A Geographical Atlas of World Weeds (Holm et al. 1979) [22].
2.4. Data Statistical Analysis
Comparisons of data among the three or four traits were subjected to one-way analysis
of variance (ANOVA), using the SPSS 16.0 statistical package. The data were checked for
normality and constant variance before analysis. The weed data were log-transformed
before analysis. Nontransformed means for weed control were reported, with statistical
interpretation based on transformed data. Treatment means were separated using the
Fisher’s protected LSD test at p= 0.05. Independent sample t-tests were employed for
comparisons with data between two sorts of traits, using SPSS 16.0. ArcGis 10.8 software
was used to draw the distribution map of sites. The data presented are means
±
SEs. To
investigate the relationships among various traits of native weeds, we performed principal
component analysis (PCA) based on the dominance values of traits collected from 666 sites.
The analysis was conducted using the “vegan” package in R version 4.2.2 to evaluate the
interactions among 13 different weed trait indicators [18,19].
3. Result
3.1. Weed Species Recorded in the Survey
A total of 287 native weed species were recorded (Table S1). These native weeds
referred to 63 families, of which Poaceae contained the most species, with up to 52 species
(
Figure 2A
), followed by Compositae (31), Polygonaceae (16), Cyperaceae (15), Fabaceae (13),
Cruciferae (12), Lamiaceae (10), Amaranthaceae (9), Euphorbiaceae (7), Apiaceae (6), Cu-
curbitaceae (5), Lythraceae (5), Caryophyllaceae (5), Rosaceae (5), and Commelinaceae (5).
Moreover, 26 families contained only one native weed species. A total of 192 genera
were involved in these 287 species, among which Echinochloa contained most native weed

Biology 2024,13, 704 5 of 17
species (9), followed by Polygonum (8). Artemisia,Eragrostis,Cyperus,Rorippa, and Rumex
all contained five species, and Setaria,Ranunculus,Solanum, and Vicia all contained four
species. There are nine genera containing three species, 27 genera containing two species,
and 145 genera containing only one species.
Biology 2024, 13, x FOR PEER REVIEW 5 of 18
A total of 287 native weed species were recorded (Table S1). These native weeds re-
ferred to 63 families, of which Poaceae contained the most species, with up to 52 species
(Figure 2A), followed by Compositae (31), Polygonaceae (16), Cyperaceae (15), Fabaceae
(13), Cruciferae (12), Lamiaceae (10), Amaranthaceae (9), Euphorbiaceae (7), Apiaceae (6),
Cucurbitaceae (5), Lythraceae (5), Caryophyllaceae (5), Rosaceae (5), and Commelinaceae
(5). Moreover, 26 families contained only one native weed species. A total of 192 genera
were involved in these 287 species, among which Echinochloa contained most native weed
species (9), followed by Polygonum (8). Artemisia, Eragrostis, Cyperus, Rorippa, and Rumex
all contained five species, and Setaria, Ranunculus, Solanum, and Vicia all contained four
species. There are nine genera containing three species, 27 genera containing two species,
and 145 genera containing only one species.
In terms of the occurrence dominance (Figure 2B), the total dominance value of Po-
aceae weeds accounted for 30% of the total weed occurrence dominance value, followed
by Compositae (13%), Fabaceae (11%), Cannabisaceae (5%), Rubiaceae (4%), Moraceae
(4%), Polygonaceae (4%), Cruciferae (3%), Amaranthaceae (3%), and Euphorbiaceae (3%).
Poaceae
18%
Compositae
10%
Polygonaceae
6%
Cyperaceae
5%
Fabaceae
5%
Brassicaceae
4%
Lamiaceae
3%
Amaranthaceae
3%
Apiaceae
2%
Euphorbiaceae
2%
Others
41%
A
Biology 2024, 13, x FOR PEER REVIEW 6 of 18
Figure 2. Species number (A) and dominance (B) of 287 native weed families.
3.2. Plant Height
Among the 287 native weed species, 31% of species were <50 cm in plant height (low),
21% of species were >100 cm (tall), and 45% were 50–100 cm (moderate) in plant height
(Figure 3A). In terms of the occurrence dominance (Figure 3B), the total dominance value
of species with moderate plant height occupied (p < 0.05) the biggest proportion of the
total weed occurrence dominance.
Figure 3. Number of native weed species (A) and average value of dominance among 666 field sur-
veying sites (B) referring to different plant heights (cm). Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B), different leers suggest
significant differences at p < 0.05.
3.3. Life Type
Poaceae
30%
Compositae
13%
Fabaceae
11%
Cannabaceae
5%
Rubiaceae
4%
Moraceae
4%
Polygonaceae
4%
Brassicaceae
3%
Amaranthace
ae 3%
Euphorbiace
ae 3%
Others
20%
B
<50
32%
50–100
46%
>100
22%
APlant
height (cm)
c
25%
a
42%
b
33%
0
1
2
3
4
5
6
<50 50–100 >100
Average value of dominance
BPlant height (cm)
Figure 2. Species number (A) and dominance (B) of 287 native weed families.

Biology 2024,13, 704 6 of 17
In terms of the occurrence dominance (Figure 2B), the total dominance value of
Poaceae weeds accounted for 30% of the total weed occurrence dominance value, followed
by Compositae (13%), Fabaceae (11%), Cannabisaceae (5%), Rubiaceae (4%), Moraceae (4%),
Polygonaceae (4%), Cruciferae (3%), Amaranthaceae (3%), and Euphorbiaceae (3%).
3.2. Plant Height
Among the 287 native weed species, 31% of species were <50 cm in plant height (low),
21% of species were >100 cm (tall), and 45% were 50–100 cm (moderate) in plant height
(Figure 3A). In terms of the occurrence dominance (Figure 3B), the total dominance value
of species with moderate plant height occupied (p< 0.05) the biggest proportion of the total
weed occurrence dominance.
Biology 2024, 13, x FOR PEER REVIEW 6 of 18
Figure 2. Species number (A) and dominance (B) of 287 native weed families.
3.2. Plant Height
Among the 287 native weed species, 31% of species were <50 cm in plant height (low),
21% of species were >100 cm (tall), and 45% were 50–100 cm (moderate) in plant height
(Figure 3A). In terms of the occurrence dominance (Figure 3B), the total dominance value
of species with moderate plant height occupied (p < 0.05) the biggest proportion of the
total weed occurrence dominance.
Figure 3. Number of native weed species (A) and average value of dominance among 666 field sur-
veying sites (B) referring to different plant heights (cm). Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B), different leers suggest
significant differences at p < 0.05.
3.3. Life Type
Poaceae
30%
Compositae
13%
Fabaceae
11%
Cannabaceae
5%
Rubiaceae
4%
Moraceae
4%
Polygonaceae
4%
Brassicaceae
3%
Amaranthace
ae 3%
Euphorbiace
ae 3%
Others
20%
B
<50
32%
50–100
46%
>100
22%
APlant
height (cm)
c
25%
a
42%
b
33%
0
1
2
3
4
5
6
<50 50–100 >100
Average value of dominance
BPlant height (cm)
Figure 3. Number of native weed species (A) and average value of dominance among 666 field
surveying sites (B) referring to different plant heights (cm). Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B), different letters suggest
significant differences at p< 0.05.
3.3. Life Type
According to the classification of life forms, 26% of the native weed species were
rosette life forms (all the leaves being basal), 47% were erect, 18% were creeping plants, and
10% were lianas (Figure 4A). Moreover, 3% of the species had noticeable thorns or hooks
(Figure 4C), and 1% were succulent plants (Figure 4E).
Biology 2024, 13, x FOR PEER REVIEW 7 of 18
According to the classification of life forms, 26% of the native weed species were ro-
see life forms (all the leaves being basal), 47% were erect, 18% were creeping plants, and
10% were lianas (Figure 4A). Moreover, 3% of the species had noticeable thorns or hooks
(Figure 4C), and 1% were succulent plants (Figure 4E).
The total dominance value of native weed species with erect form occupied the big-
gest proportion of the total weed occurrence dominance, and the proportion decreased
from 47% in species richness to 37% in occurrence dominance. Rosee plants also showed
a decrease in the proportion of native weed occurrence dominance, compared to species
richness. Meanwhile, the total dominance value of native liana weed species occupied 32%
of the total native weed occurrence dominance, and the proportion was much higher than
the proportion in species richness (Figure 4B). Besides, the proportions of occurrence dom-
inance of native weed species with thorns and succulent plants were 6% and 1%, respec-
tively (Figure 4D,F).
Rosette
26%
Creeping
17%
Liana
10%
Erect
47%
A
c
15%
c
16%
b
32%
a
37%
0
0.5
1
1.5
2
2.5
3
Average value of dominance
B
Yes
3%
No
97%
C
Thorny
b
6%
a
94%
0
2
4
6
8
10
12
Yes No
Average value of dominance
D
Thorny
Yes
1%
No
99%
E
Succulent
b
1%
a
99%
0
2
4
6
8
10
12
14
Yes No
Average value of dominance
FSucculent
Figure 4. Cont.

Biology 2024,13, 704 7 of 17
Biology 2024, 13, x FOR PEER REVIEW 7 of 18
According to the classification of life forms, 26% of the native weed species were ro-
see life forms (all the leaves being basal), 47% were erect, 18% were creeping plants, and
10% were lianas (Figure 4A). Moreover, 3% of the species had noticeable thorns or hooks
(Figure 4C), and 1% were succulent plants (Figure 4E).
The total dominance value of native weed species with erect form occupied the big-
gest proportion of the total weed occurrence dominance, and the proportion decreased
from 47% in species richness to 37% in occurrence dominance. Rosee plants also showed
a decrease in the proportion of native weed occurrence dominance, compared to species
richness. Meanwhile, the total dominance value of native liana weed species occupied 32%
of the total native weed occurrence dominance, and the proportion was much higher than
the proportion in species richness (Figure 4B). Besides, the proportions of occurrence dom-
inance of native weed species with thorns and succulent plants were 6% and 1%, respec-
tively (Figure 4D,F).
Rosette
26%
Creeping
17%
Liana
10%
Erect
47%
A
c
15%
c
16%
b
32%
a
37%
0
0.5
1
1.5
2
2.5
3
Average value of dominance
B
Yes
3%
No
97%
C
Thorny
b
6%
a
94%
0
2
4
6
8
10
12
Yes No
Average value of dominance
D
Thorny
Yes
1%
No
99%
E
Succulent
b
1%
a
99%
0
2
4
6
8
10
12
14
Yes No
Average value of dominance
FSucculent
Figure 4. Number of native weed species (A,C,E) and average value of dominance among 666 field
surveying sites (B,D,F) referring to different life types. Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B,D,F) different letters suggest
significant differences at p< 0.05.
The total dominance value of native weed species with erect form occupied the biggest
proportion of the total weed occurrence dominance, and the proportion decreased from
47% in species richness to 37% in occurrence dominance. Rosette plants also showed a
decrease in the proportion of native weed occurrence dominance, compared to species
richness. Meanwhile, the total dominance value of native liana weed species occupied
32% of the total native weed occurrence dominance, and the proportion was much higher
than the proportion in species richness (Figure 4B). Besides, the proportions of occurrence
dominance of native weed species with thorns and succulent plants were 6% and 1%,
respectively (Figure 4D,F).
3.4. Drought Resistance
Among the 287 native weed species recorded, only 7% of species richness and occur-
rence dominance were aquatic plants (Figure 5A). Phragmites australis and Leersia hexandra
can occur in aquatic and terrestrial habitats and thus were included in the list of aquatic
and terrestrial weed species here. According to the adaptability to drought conditions, ter-
restrial weed species were further divided into three categories: hygrophytes (not tolerant
to drought stress), xerophytes (drought tolerance), and mesophytes (with drought tolerance
between hygrophytes and xerophytes). Mesophytes occupied the biggest proportion of
native weed species in species richness (48%) but not in occurrence dominance (37%). Xero-
phytes showed an increase in the proportion of native weed species from species richness
(25%) to occurrence dominance (48%). In comparison, hygrophytes showed a decrease in
the proportion of native weed species from species richness (20%) to occurrence dominance
(9%) (Figure 5B).

Biology 2024,13, 704 8 of 17
Biology 2024, 13, x FOR PEER REVIEW 8 of 18
Figure 4. Number of native weed species (A,C,E) and average value of dominance among 666 field
surveying sites (B,D,F) referring to different life types. Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B,D,F) different leers suggest
significant differences at p < 0.05.
3.4. Drought Resistance
Among the 287 native weed species recorded, only 7% of species richness and occur-
rence dominance were aquatic plants (Figure 5A). Phragmites australis and Leersia hexandra
can occur in aquatic and terrestrial habitats and thus were included in the list of aquatic
and terrestrial weed species here. According to the adaptability to drought conditions,
terrestrial weed species were further divided into three categories: hygrophytes (not tol-
erant to drought stress), xerophytes (drought tolerance), and mesophytes (with drought
tolerance between hygrophytes and xerophytes). Mesophytes occupied the biggest pro-
portion of native weed species in species richness (48%) but not in occurrence dominance
(37%). Xerophytes showed an increase in the proportion of native weed species from spe-
cies richness (25%) to occurrence dominance (48%). In comparison, hygrophytes showed
a decrease in the proportion of native weed species from species richness (20%) to occur-
rence dominance (9%) (Figure 5B).
Figure 5. Number of native weed species (A) and average value of dominance among 666 field sur-
veying sites (B) referring to different drought resistance. Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B), different leers suggest
significant differences at p < 0.05.
3.5. Shade Tolerance
According to the abilities in shade tolerance, weed species were divided into three
categories: shade plants (adapted to under-canopy conditions), sun plants (plants that
grow and develop vigorously in strong light environments and grow poorly under shade
and weak light conditions), and moderate plants (plants holding shade tolerance between
sun plants and shade plants). Among the 287 recorded native weed species (Figure 6A,B),
a majority were moderate plants in both species richness (81%) and occurrence dominance
(94%).
Aquatic
7%
Hygrophyte
20%
Mesophyte
48%
Xerophyte
25%
A
c
7%
c
9%
b
37%
a
48%
0
1
2
3
4
5
6
Average value of dominance
B
Figure 5. Number of native weed species (A) and average value of dominance among 666 field sur-
veying sites (B) referring to different drought resistance. Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B), different letters suggest
significant differences at p< 0.05.
3.5. Shade Tolerance
According to the abilities in shade tolerance, weed species were divided into three cate-
gories: shade plants (adapted to under-canopy conditions), sun plants (plants that grow and
develop vigorously in strong light environments and grow poorly under shade and weak
light conditions), and moderate plants (plants holding shade tolerance between sun plants
and shade plants). Among the 287 recorded native weed species (Figure 6A,B), a majority
were moderate plants in both species richness (81%) and occurrence dominance (94%).
Biology 2024, 13, x FOR PEER REVIEW 9 of 18
Figure 6. Number of native weed species (A) and average value of dominance among 666 field sur-
veying sites (B) referring to different shade tolerance. Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B), different leers suggest
significant differences at P < 0.05.
3.6. Life History Trait
Among the 287 native weed species, 55% were perennials, while the total occurrence
dominance of perennials was significantly much lower than those of annual or biennial
weeds (Figure 7A,B).
Figure 7. Number of native weed species (A) and average value of dominance among 666 field sur-
veying sites (B) referring to different life history traits. Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B), different leers suggest
significant differences at P < 0.05.
3.7. Reproductive Characteristics
Among the 287 native weed species recorded, 18% species held low fertility (seed
production per plant usually <200) (Figure 8A), 34% held moderate fertility (seed produc-
tion per plant usually between 200 and 2000), 29% held high fertility (seed production per
plant usually between 2001 and 20,000), and 19% held very high fertility (seed production
per plant usually >20,000). Regarding occurrence dominance (Figure 8B), native weed spe-
cies holding very high fertility increased in proportion out of the total native weeds, from
19% in species richness to 42% in occurrence dominance. Moreover, the native weed spe-
cies holding moderate fertility showed a big decrease in the proportion, from 34% in spe-
cies richness to 15% in occurrence dominance.
Sun plant
5% Shade
plant
14%
Moderate
light
81%
A
b
2%
b
4%
a
94%
0
1
2
3
4
5
Sun plant Shade
plant
Moderate
light
Average value of dominance
B
Perennial
55%
Annual or
biennial
45%
A
b
32%
a
68%
0
2
4
6
8
10
Perennial Annual or
biennial
Average value of dominance
B
Figure 6. Number of native weed species (A) and average value of dominance among 666 field
surveying sites (B) referring to different shade tolerance. Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B), different letters suggest
significant differences at p< 0.05.
3.6. Life History Trait
Among the 287 native weed species, 55% were perennials, while the total occurrence
dominance of perennials was significantly much lower than those of annual or biennial
weeds (Figure 7A,B).

Biology 2024,13, 704 9 of 17
Biology 2024, 13, x FOR PEER REVIEW 9 of 18
Figure 6. Number of native weed species (A) and average value of dominance among 666 field sur-
veying sites (B) referring to different shade tolerance. Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B), different leers suggest
significant differences at P < 0.05.
3.6. Life History Trait
Among the 287 native weed species, 55% were perennials, while the total occurrence
dominance of perennials was significantly much lower than those of annual or biennial
weeds (Figure 7A,B).
Figure 7. Number of native weed species (A) and average value of dominance among 666 field sur-
veying sites (B) referring to different life history traits. Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B), different leers suggest
significant differences at P < 0.05.
3.7. Reproductive Characteristics
Among the 287 native weed species recorded, 18% species held low fertility (seed
production per plant usually <200) (Figure 8A), 34% held moderate fertility (seed produc-
tion per plant usually between 200 and 2000), 29% held high fertility (seed production per
plant usually between 2001 and 20,000), and 19% held very high fertility (seed production
per plant usually >20,000). Regarding occurrence dominance (Figure 8B), native weed spe-
cies holding very high fertility increased in proportion out of the total native weeds, from
19% in species richness to 42% in occurrence dominance. Moreover, the native weed spe-
cies holding moderate fertility showed a big decrease in the proportion, from 34% in spe-
cies richness to 15% in occurrence dominance.
Sun plant
5% Shade
plant
14%
Moderate
light
81%
A
b
2%
b
4%
a
94%
0
1
2
3
4
5
Sun plant Shade
plant
Moderate
light
Average value of dominance
B
Perennial
55%
Annual or
biennial
45%
A
b
32%
a
68%
0
2
4
6
8
10
Perennial Annual or
biennial
Average value of dominance
B
Figure 7. Number of native weed species (A) and average value of dominance among 666 field
surveying sites (B) referring to different life history traits. Note that each percentage value represents
the proportion of each trait within the same group of indicators. In (B), different letters suggest
significant differences at p< 0.05.
3.7. Reproductive Characteristics
Among the 287 native weed species recorded, 18% species held low fertility (seed pro-
duction per plant usually <200) (Figure 8A), 34% held moderate fertility (seed production
per plant usually between 200 and 2000), 29% held high fertility (seed production per plant
usually between 2001 and 20,000), and 19% held very high fertility (seed production per
plant usually >20,000). Regarding occurrence dominance (Figure 8B), native weed species
holding very high fertility increased in proportion out of the total native weeds, from 19%
in species richness to 42% in occurrence dominance. Moreover, the native weed species
holding moderate fertility showed a big decrease in the proportion, from 34% in species
richness to 15% in occurrence dominance.
Regarding the size (Figure 8C), 33% out of the total 287 native weed species were tiny
(<2 mm in diameter or length), 46% were moderate (2–4 mm in diameter or 2–6 mm in
length), and 21% were bigger (>4 mm in diameter or >6 mm in length). Native weed species
with moderate seeds occupied more than half (51%) of the total occurrence dominance of
the overall native weed species, and native weed species with bigger seeds showed an
increase from 21% in species richness to 28% in occurrence dominance (Figure 8D).
Regarding the ability of natural vegetative reproduction (Figure 8E), weed species were
divided into three categories: low (plants usually do not reproduce and spread by leaves,
roots, or stems), strong (plants readily reproduce and spread by leaves, roots, or stems),
and moderate (plants hold the ability of vegetative reproduction but usually reproduce
and spread by seeds). Among the 287 native weed species, 46% held a low ability, 36%
held a moderate ability, and 18% held a strong ability of vegetative reproduction. In terms
of occurrence dominance, species holding a moderate ability of vegetative reproduction
occupied the highest proportion out of the total occurrence dominance of the overall native
weed species (Figure 8F).

Biology 2024,13, 704 10 of 17
Biology 2024, 13, x FOR PEER REVIEW 10 of 18
Regarding the size (Figure 8C), 33% out of the total 287 native weed species were tiny
(<2 mm in diameter or length), 46% were moderate (2–4 mm in diameter or 2–6 mm in
length), and 21% were bigger (>4 mm in diameter or >6 mm in length). Native weed spe-
cies with moderate seeds occupied more than half (51%) of the total occurrence dominance
of the overall native weed species, and native weed species with bigger seeds showed an
increase from 21% in species richness to 28% in occurrence dominance (Figure 8D).
Regarding the ability of natural vegetative reproduction (Figure 8E), weed species
were divided into three categories: low (plants usually do not reproduce and spread by
leaves, roots, or stems), strong (plants readily reproduce and spread by leaves, roots, or
stems), and moderate (plants hold the ability of vegetative reproduction but usually re-
produce and spread by seeds). Among the 287 native weed species, 46% held a low ability,
36% held a moderate ability, and 18% held a strong ability of vegetative reproduction. In
terms of occurrence dominance, species holding a moderate ability of vegetative repro-
duction occupied the highest proportion out of the total occurrence dominance of the
overall native weed species (Figure 8F).
<200
18%
200–
2000
34%
2000–
20,000
29%
>20,000
19%
A
Seed production per plant
d
12%
c
15%
b
31%
a
42%
0
1
2
3
4
5
6
<200 200–
2000
2000–
20,000
>20,000
Average value of dominance
B
Seed production per plant
Diameter or
length <2
33%
Diameter:
2–4 or
length: 2–6
46%
Diameter >4 or
length >6
21%
C
Size
(mm)
c
20%
a
51%
b
28%
0
1
2
3
4
5
6
7
Diameter or
length <2
Diameter:
2–4 or
length: 2–6
Diameter >4
or length >6
Average value of dominance
D
Size
(mm)
Biology 2024, 13, x FOR PEER REVIEW 11 of 18
Figure 8. Number of native weed species (A,C,E) and average value of dominance among 666 field
surveying sites (B,D,F) referring to different reproductive characteristics. Note that each percentage
value represents the proportion of each trait within the same group of indicators. In (B,D,F), differ-
ent leers suggest significant differences at P < 0.05.
3.8. Appendages of Fruits
Among the 287 native weed species (Figure 9A), 1% held mucilage on the fruit sur-
face, fruits of 12% of the species showed obvious hairs, fruits of 7% of the species showed
thorns or awns, and 80% of the species did not show mucilage, obvious hairs, thorns or
awns. With regards to occurrence dominance, the proportions of native weeds with fruits
holding appendages, including obvious hairs, thorns, or awns, occupied increasing pro-
portions compared with the proportions in species richness. Whereas 70% of the occur-
rence dominance was still occupied by native weeds with fruits without the above ap-
pendages (Figure 9B).
Figure 9. Number of native weed species (A) and average value of dominance among 666 field sur-
veying sites (B) referring to different appendages of fruits. Note that each percentage value repre-
sents the proportion of each trait within the same group of indicators. In (B), different leers suggest
significant differences at P < 0.05.
3.9. Herbicide Resistance and Weediness
Among the 287 native weed species, 31% were found to have herbicide-resistant pop-
ulations or biotypes worldwide (Figure 10A), which occupied 57% occurrence dominance
out of the total native weeds (Figure 10B). According to A Geographical Atlas of World Weeds
Strong
18%
No
46%
Moderate
36%
E
Vegetative reproduction
c
19%
b
33%
a
48%
0
1
2
3
4
5
Strong No Moderate
Average value of dominance
F
Vegetative reproduction
Mucilage
1%
Thorns or
awns
7%
Obvious hairs
12%
None of
above
80%
A
d
0.3%
c
13%
b
17%
a
70%
0
2
4
6
8
10
Mucilage Thorns
or awns
Obvious
hairs
None of
above
Average value of dominance
B
Figure 8. Number of native weed species (A,C,E) and average value of dominance among 666 field
surveying sites (B,D,F) referring to different reproductive characteristics. Note that each percentage
value represents the proportion of each trait within the same group of indicators. In (B,D,F), different
letters suggest significant differences at p< 0.05.
3.8. Appendages of Fruits
Among the 287 native weed species (Figure 9A), 1% held mucilage on the fruit surface,
fruits of 12% of the species showed obvious hairs, fruits of 7% of the species showed
thorns or awns, and 80% of the species did not show mucilage, obvious hairs, thorns
or awns. With regards to occurrence dominance, the proportions of native weeds with

Biology 2024,13, 704 11 of 17
fruits holding appendages, including obvious hairs, thorns, or awns, occupied increasing
proportions compared with the proportions in species richness. Whereas 70% of the
occurrence dominance was still occupied by native weeds with fruits without the above
appendages (Figure 9B).
Biology 2024, 13, x FOR PEER REVIEW 11 of 18
Figure 8. Number of native weed species (A,C,E) and average value of dominance among 666 field
surveying sites (B,D,F) referring to different reproductive characteristics. Note that each percentage
value represents the proportion of each trait within the same group of indicators. In (B,D,F), differ-
ent leers suggest significant differences at P < 0.05.
3.8. Appendages of Fruits
Among the 287 native weed species (Figure 9A), 1% held mucilage on the fruit sur-
face, fruits of 12% of the species showed obvious hairs, fruits of 7% of the species showed
thorns or awns, and 80% of the species did not show mucilage, obvious hairs, thorns or
awns. With regards to occurrence dominance, the proportions of native weeds with fruits
holding appendages, including obvious hairs, thorns, or awns, occupied increasing pro-
portions compared with the proportions in species richness. Whereas 70% of the occur-
rence dominance was still occupied by native weeds with fruits without the above ap-
pendages (Figure 9B).
Figure 9. Number of native weed species (A) and average value of dominance among 666 field sur-
veying sites (B) referring to different appendages of fruits. Note that each percentage value repre-
sents the proportion of each trait within the same group of indicators. In (B), different leers suggest
significant differences at P < 0.05.
3.9. Herbicide Resistance and Weediness
Among the 287 native weed species, 31% were found to have herbicide-resistant pop-
ulations or biotypes worldwide (Figure 10A), which occupied 57% occurrence dominance
out of the total native weeds (Figure 10B). According to A Geographical Atlas of World Weeds
Strong
18%
No
46%
Moderate
36%
E
Vegetative reproduction
c
19%
b
33%
a
48%
0
1
2
3
4
5
Strong No Moderate
Average value of dominance
F
Vegetative reproduction
Mucilage
1%
Thorns or
awns
7%
Obvious hairs
12%
None of
above
80%
A
d
0.3%
c
13%
b
17%
a
70%
0
2
4
6
8
10
Mucilage Thorns
or awns
Obvious
hairs
None of
above
Average value of dominance
B
Figure 9. Number of native weed species (A) and average value of dominance among 666 field
surveying sites (B) referring to different appendages of fruits. Note that each percentage value
represents the proportion of each trait within the same group of indicators. In (B), different letters
suggest significant differences at p< 0.05.
3.9. Herbicide Resistance and Weediness
Among the 287 native weed species, 31% were found to have herbicide-resistant popu-
lations or biotypes worldwide (Figure 10A), which occupied 57% occurrence dominance out
of the total native weeds (Figure 10B). According to A Geographical Atlas of World Weeds [
23
],
31% out of the total 287 native weed species were recorded as a serious weed in at least one
country or area (Figure 10C), 18% were recorded as a principal weed in at least one country
or area but not recorded as a serious weed, 27% were recorded as a common weed in at
least one country or area but not recorded as a serious or principal weed, and the remaining
24% were listed as holding unclear weediness. Serious weeds showed a significantly higher
proportion (47%) in occurrence dominance among the overall native weeds (Figure 10D).
Moreover, the total occurrence dominance values of weed groups increased with increasing
weediness.
Biology 2024, 13, x FOR PEER REVIEW 12 of 18
[23], 31% out of the total 287 native weed species were recorded as a serious weed in at
least one country or area (Figure 10C), 18% were recorded as a principal weed in at least
one country or area but not recorded as a serious weed, 27% were recorded as a common
weed in at least one country or area but not recorded as a serious or principal weed, and
the remaining 24% were listed as holding unclear weediness. Serious weeds showed a
significantly higher proportion (47%) in occurrence dominance among the overall native
weeds (Figure 10D). Moreover, the total occurrence dominance values of weed groups
increased with increasing weediness.
Figure 10. Number of native weed species (A,C) and average value of dominance among 666 field
surveying sites (B,D) referring to different herbicide resistance potential. Note that each percentage
value represents the proportion of each trait within the same group of indicators. In (B,D), different
leers suggest significant differences at P < 0.05.
3.10. PCA of Weed Traits
The results extracted from the PCA show that 81.8% of the total variance of the data
obtained could be explained using the first two principal components (Figure 11). Accord-
ing to the PCA results, the traits of native weeds could be organized into 3 groups. Group
1 is composed of serious weeds recorded in “A Geographical Atlas of World Weeds”, herbi-
cide resistance, non-perennial, no vegetative reproduction, moderate plant height (50–100
cm), and xerophyte referring to drought tolerance. Group 2 is composed of principal weed
and various weed traits. Group 3 is composed of common weeds and plants with unclear
weediness, hairy fruits, big seeds, perennials, tall plants, moderate vegetative reproduc-
tion, and mesophytes referring to drought resistance.
No
69%
Yes
31%
A
Herbicide resistance
43%
57%
0
1
2
3
4
5
6
7
No Yes
Average value of dominance
B
Herbicide
resistance
Unclear
24%
Common
27%
Principal
18%
Serious
31%
CWeediness
d
13%
c
18%
b
21%
a
47%
0
10
20
30
40
50
Average value of dominance
Weediness
D
Figure 10. Cont.

Biology 2024,13, 704 12 of 17
Biology 2024, 13, x FOR PEER REVIEW 12 of 18
[23], 31% out of the total 287 native weed species were recorded as a serious weed in at
least one country or area (Figure 10C), 18% were recorded as a principal weed in at least
one country or area but not recorded as a serious weed, 27% were recorded as a common
weed in at least one country or area but not recorded as a serious or principal weed, and
the remaining 24% were listed as holding unclear weediness. Serious weeds showed a
significantly higher proportion (47%) in occurrence dominance among the overall native
weeds (Figure 10D). Moreover, the total occurrence dominance values of weed groups
increased with increasing weediness.
Figure 10. Number of native weed species (A,C) and average value of dominance among 666 field
surveying sites (B,D) referring to different herbicide resistance potential. Note that each percentage
value represents the proportion of each trait within the same group of indicators. In (B,D), different
leers suggest significant differences at P < 0.05.
3.10. PCA of Weed Traits
The results extracted from the PCA show that 81.8% of the total variance of the data
obtained could be explained using the first two principal components (Figure 11). Accord-
ing to the PCA results, the traits of native weeds could be organized into 3 groups. Group
1 is composed of serious weeds recorded in “A Geographical Atlas of World Weeds”, herbi-
cide resistance, non-perennial, no vegetative reproduction, moderate plant height (50–100
cm), and xerophyte referring to drought tolerance. Group 2 is composed of principal weed
and various weed traits. Group 3 is composed of common weeds and plants with unclear
weediness, hairy fruits, big seeds, perennials, tall plants, moderate vegetative reproduc-
tion, and mesophytes referring to drought resistance.
No
69%
Yes
31%
A
Herbicide resistance
43%
57%
0
1
2
3
4
5
6
7
No Yes
Average value of dominance
B
Herbicide
resistance
Unclear
24%
Common
27%
Principal
18%
Serious
31%
CWeediness
d
13%
c
18%
b
21%
a
47%
0
10
20
30
40
50
Average value of dominance
Weediness
D
Figure 10. Number of native weed species (A,C) and average value of dominance among 666 field
surveying sites (B,D) referring to different herbicide resistance potential. Note that each percentage
value represents the proportion of each trait within the same group of indicators. In (B,D), different
letters suggest significant differences at p< 0.05.
3.10. PCA of Weed Traits
The results extracted from the PCA show that 81.8% of the total variance of the data
obtained could be explained using the first two principal components (Figure 11). Accord-
ing to the PCA results, the traits of native weeds could be organized into 3 groups. Group 1
is composed of serious weeds recorded in “A Geographical Atlas of World Weeds”, herbicide
resistance, non-perennial, no vegetative reproduction, moderate plant height
(50–100 cm
),
and xerophyte referring to drought tolerance. Group 2 is composed of principal weed
and various weed traits. Group 3 is composed of common weeds and plants with unclear
weediness, hairy fruits, big seeds, perennials, tall plants, moderate vegetative reproduction,
and mesophytes referring to drought resistance.
Biology 2024, 13, x FOR PEER REVIEW 13 of 18
Figure 11. Principal component analysis (PCA) showing the 13 weed trait indicators. Note that the
codes of indicators are the same as in Table 2.
4. Discussion
4.1. Native Weed Diversity in Agricultural Areas
Based on the surveys of hundreds of field sites in agricultural areas, this is the first
study to reveal the diversity of native weed flora in a city in China. Weed Flora of China
[24] listed 1454 weed species, and Alien Invasive Flora of China [25] listed 403 alien inva-
sive plant species in China. Thus, a list of 1360 native weed species was generated. The
surveyed city, Yangzhou, represents about 0.07% of the land area in mainland China,
while the number of native weed species represents about 21% of the total native weed
species in China. Hence, as a city in eastern China, Yangzhou has a rich diversity of weed
flora species. Meanwhile, eastern China is also one of the hoest areas suffering alien plant
invasions, and a relatively effective risk assessment system is urgently needed. The con-
clusions from this study can provide reference and suggestions for the establishment of
such a risk assessment system in the future.
Poaceae is a species-rich plant family consisting of about 10,000 species (commonly
called grasses), including the most economically important plants [26]. It has been sug-
gested that the genomes of Poaceae have evolved at an elevated rate due to the selection
imposed by changing environmental conditions and more recent breeding efforts [27,28].
Figure 11. Principal component analysis (PCA) showing the 13 weed trait indicators. Note that the
codes of indicators are the same as in Table 2.

Biology 2024,13, 704 13 of 17
4. Discussion
4.1. Native Weed Diversity in Agricultural Areas
Based on the surveys of hundreds of field sites in agricultural areas, this is the first
study to reveal the diversity of native weed flora in a city in China. Weed Flora of China [
24
]
listed 1454 weed species, and Alien Invasive Flora of China [
25
] listed 403 alien invasive
plant species in China. Thus, a list of 1360 native weed species was generated. The
surveyed city, Yangzhou, represents about 0.07% of the land area in mainland China, while
the number of native weed species represents about 21% of the total native weed species in
China. Hence, as a city in eastern China, Yangzhou has a rich diversity of weed flora species.
Meanwhile, eastern China is also one of the hottest areas suffering alien plant invasions,
and a relatively effective risk assessment system is urgently needed. The conclusions
from this study can provide reference and suggestions for the establishment of such a risk
assessment system in the future.
Poaceae is a species-rich plant family consisting of about 10,000 species (commonly
called grasses), including the most economically important plants [
26
]. It has been sug-
gested that the genomes of Poaceae have evolved at an elevated rate due to the selection
imposed by changing environmental conditions and more recent breeding efforts [
27
,
28
].
Grasses usually represent the most troublesome weed groups in various agricultural areas,
particularly in cereal crops. For example, many species of grassy weeds have become the
dominant malignant weeds in wheat, rice, and corn fields worldwide [
29
,
30
]. In our survey,
grassy weeds also occupied the biggest proportions in both species richness (18%) and
occurrence dominance (30%) out of the total native weed species. Hence, alien plant species
belonging to Poaceae should be highlighted with higher scores in risk-assessing systems
for agricultural areas.
Compositae is one of the largest and most diverse plant families in the world, with
more than 26,000 species, accounting for about 7% of the existing flowering plants [
31
].
Compositae is distributed across all regions of the world regions except for Antarctica
[32,33]
and exists in almost all habitats [
34
]. In addition, many Compositae plants are used as
medicine and/or food plants [35]. Regarding alien plant invasions, Compositae plants ac-
count for 10% of the world’s naturalized alien plants, which is the biggest plant family [
36
].
In this study, Compositae was second to Poaceae in both species richness and occurrence
dominance of native weeds. Hence, alien plant species belonging to Compositae should
also be highlighted with higher scores in risk-assessing systems for agricultural areas.
Moreover, Fabaceae should also be highlighted in risk-assessing systems for agricultural
areas. Fabaceae is the third largest plant family after Compositae and Orchidaceae in the
world, with about 19,500 species [
37
–
39
]. Fabaceae are usually rich in protein and are
the main dietary source in many countries and regions, and many Fabaceae plant species
are crops or medicine plants [
39
,
40
]. In the list of alien invasive plant species, Fabaceae
account for 15% in South Asia [
41
], 7% in Europe [
42
], and 11% in China [
43
]. In addition,
among the 287 native weed species, Cyperaceae, Cruciferae, Labiatae, and Polygonaceae
also accounted for a higher proportion. It is recommended to pay attention to these plant
families in risk-assessing systems for agricultural areas. For example, Cyperaceae is the
second largest weed group after Poaceae weeds [44].
4.2. Traits Closely Related to Weediness in Agricultural Areas
To date, several countries or areas have established alien plant invasion risk assess-
ment systems, such as Australia, the United States, New Zealand, Central Europe, and
China
[5,9,11,20]
. In China, there were studies that established alien plant invasion risk as-
sessment systems on a regional scale, for example, for Xiamen City [
21
] or Ningbo City [
45
].
These risk assessment systems were mainly based on assignments of life history traits of
plants. Together, our results suggested significant differences in relationships between
different traits and occurrence dominance in native weed species in agricultural areas.
Weeds live in habitats with high levels of human disturbances, particularly in agricul-
tural areas, where weed management practices are frequent and periodic. Weeds adopting

Biology 2024,13, 704 14 of 17
the R strategy [
46
] are more adapted to agricultural environments, which learn to gener-
ate many seeds in a shorter life span, such as annuals or biennials with high fertility [
1
].
Meanwhile, perennials with high fertility and vegetative reproduction could also be highly
adapted to agricultural environments, as vegetative reproduction facilitates the coloniza-
tion and diffusion of weeds [
47
]. In our study, native weeds holding a shorter life span
(annuals of biennials) were more dominant than perennials; native weeds holding moderate
ability of vegetative reproduction were more dominant than those holding high ability of
vegetative reproduction; and native weeds holding high fertility showed big competitive
advantages reflected by occurrence dominance. Interestingly, native weeds with moderate
seed sizes showed big competitive advantages compared with those with big seeds or those
with tiny seeds. Agricultural environments are usually characterized by rich resources for
plant growth. Quick emergence from soil layers and fast growth could be important to
occupy great advantages in these habitats. The nutrition contained in seeds is almost the
only source of seedling emergence and very early growth. Thus, the moderate seed sizes
outweigh the tiny seeds. Moreover, given the limited nutrition in a plant, large seeds often
result in much lower seed production. Considering that weeds recorded in agricultural
areas tend to be non-perennial with a plant height of < 1 m, moderate seed sizes also
outweigh large seeds.
In agricultural areas usually holding rich resources, taller weed species might quickly
occupy preferable niches and form dominant communities [
48
]. Whereas tall weeds are also
more likely to attract attention for weed management. Weeds with moderate plant height
showed advantages compared with tall or low weeds. Moreover, tall plants commonly
need longer periods for growing, which may be frequently disturbed by weed management
practices. Erect plants were most common among native weed species in the agricultural
area surveyed. In addition, the upright plant surface is relatively less exposed to herbicides,
and thus, many troublesome weed species holding serious herbicide resistance are erect
plants [
49
]. Moreover, lianas showed competitive advantages in occurrence dominance
for achieving a larger area of coverage with smaller biomass. Succulent plants usually
grow slower, have a higher ability to adapt to drought stress, and are not advantageous in
capricious agricultural environments with rich resources. Although studies have shown
that plants with thorns are more likely to become invasive alien plants [
5
], plants with
obvious thorns are frequently controlled in agricultural areas due to their potential to cause
stab wounds.
Kuester et al. [
50
] reported that hygrophytes are more likely to become invasive plants.
At the same time, our survey suggested that xerophytes and mesophytes accounted for
73% of the species richness and 85% of the occurrence dominance among the overall native
weeds. In eastern China, most crops are highland crops, and highlands host most native
weed species. In addition, the weed diversity in paddy fields in eastern China is relatively
lower, among which many weed species occurring on paddy fields are mesophytes, such
as Echinochloa spp., Leptochloa chinensis, and Cyperus iria [51].
A Geographical Atlas of World Weeds [
22
] provides a comprehensive international review
of approximately 8000 species of weeds, compiling geographic distributions for the coun-
tries or areas where a species is known to occur as a weed of serious, principal, common, or
unknown seriousness (ranking provided by a weed scientist from that country), or where it
is present in the general flora but not known to act as a weed. Our survey suggested that
the occurrence dominance of native weeds increased with increasing weediness of native
weed groups. Therefore, this book could still be an important reference for risk-assessing
systems for agricultural areas.
Moreover, the PCA indicated that serious weeds were more likely to exhibit traits
such as evolving herbicide resistance, herbicide resistance, non-perennial growth, lack of
vegetative reproduction, moderate plant height, and xerophytic characteristics associated
with drought tolerance. Therefore, these traits should be emphasized when assessing the
invasive risks of introducing plants into agricultural areas.

Biology 2024,13, 704 15 of 17
Applying chemical herbicides is the most important weed management strategy in
agricultural areas [
52
,
53
]. Many weed species have evolved resistance to various herbi-
cides and caused serious damage to agriculture worldwide [
54
]. Weed species that have
evolved herbicide resistance are frequently characterized by high fertility to produce a
large number of offspring with high genetic diversity for herbicide selection, or they are
highly adapted to certain or many kinds of agricultural habitats, or they have a high ability
for regrowth or quick seedling growth to escape herbicide applications. Thus, herbicide-
resistant weed species might also be very troublesome and evolve herbicide resistance in
introduced regions. On the other hand, herbicide-resistant populations or biotypes might
be directly introduced into new regions by various means [
55
]. Therefore, information
on herbicide resistance elsewhere could also be important for risk-assessing systems for
agricultural areas.
5. Conclusions
This study underscored the high diversity of native weeds and their adaptive charac-
teristics in eastern China and highlighted the predominance of Poaceae and Compositae
in both species richness and occurrence dominance. Together, our results indicated that
native weeds with high fertility, moderate seed sizes, shorter life spans, and intermediate
vegetative reproduction abilities tend to exhibit greater dominance, reflecting their adap-
tive strategies in agricultural environments. Moreover, traits such as plant height, growth
form, and herbicide resistance play crucial roles in weed competitiveness and management
challenges. The observed patterns and traits of the native weeds offer valuable information
for understanding their ecological roles and improving weed management practices in
agricultural landscapes. The insights are pivotal for refining risk assessment systems for
plant invasions in agricultural areas and developing targeted management strategies.
Supplementary Materials: The following supporting information can be downloaded at: https://
www.mdpi.com/article/10.3390/biology13090704/s1, Table S1: 287 species of native weeds and their
families were investigated.
Author Contributions: Conceptualization, G.C., Z.H., K.A., Y.C., and J.X.; Methodology, G.C., Z.H.,
and K.A.; Software, G.C., Z.H., K.A., Y.C., and J.X.; Validation, G.C., Z.H., K.A., and J.X.; Formal
analysis, G.C.; Investigation, G.C., Z.H., K.A., Y.C., and J.X.; Resources, G.C.; Data curation, G.C.,
Z.H., Y.C., and J.X.; Writing—original draft, G.C., Z.H., and Y.C.; Writing—review and editing, G.C.
and Z.H.; Visualization, G.C.; Supervision, G.C.; Project administration, G.C.; Funding acquisition,
G.C. All authors have read and agreed to the published version of the manuscript.
Funding: This research was funded by a project funded by the Jiangsu Key R&D Plan (BE2022338)
and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The original contributions presented in the study are included in the
article and Supplementary Material.
Acknowledgments: We thank Hongcheng Zhang for his guidance on this study.
Conflicts of Interest: The authors declare that they have no competing financial interests or personal
relationships that could have influenced the work reported in this study.
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