An integrated assessment of the vascular plant species of the Americas

Abstract

The vascular plants of the Americas
Botanical exploration in the Americas has a history that stretches back for half a millennium, with knowledge assembled in diverse regional floras and lists. Ulloa Ulloa et al. present a comprehensive and integrated compilation of all known native New World vascular plant species (see the Perspective by Givnish). This compilation, in a publicly available, searchable database, includes 124,993 species—about one-third of the worldwide total. They further present details of the distribution of species across families and genera, the geographical foci of diversity, and the floristic relationships between regions. The rate of plant species discovery in the Americas averages almost 750 annually, so this valuable resource will continue to grow.
Science , this issue p. 1614 ; see also p. 1535

Full text

FLORISTICS
An integrated assessment of the
vascular plant species of
the Americas
Carmen Ulloa Ulloa,
1
*Pedro Acevedo-Rodríguez,
2
Stephan Beck,
3
Manuel J. Belgrano,
4
Rodrigo Bernal,
5
Paul E. Berry,
6
Lois Brako,
7
Marcela Celis,
8,9
Gerrit Davidse,
1
Rafaela C. Forzza,
10
S. Robbert Gradstein,
11
Omaira Hokche,
12
Blanca León,
13,14
Susana León-Yánez,
15
Robert E. Magill,
1
David A. Neill,
16
Michael Nee,
1
Peter H. Raven,
1
Heather Stimmel,
1
Mark T. Strong,
2
José L. Villaseñor,
17
James L. Zarucchi,
1
Fernando O. Zuloaga,
4
Peter M. Jørgensen
1
The cataloging of the vascular plants of the Americas has a centuries-long history, but it is
only in recent decades that an overview of the entire flora has become possible. We present an
integrated assessment of all known native species of vascular plants in the Americas.
Twelve regional and national checklists, prepared over the past 25 years and including two
large ongoing flora projects, were merged into a single list. Our publicly searchable checklist
includes 124,993 species, 6227 genera, and 355 families, which correspond to 33% of the
383,671 vascular plant species known worldwide. In the past 25 years, the rate at which new
species descriptions are added has averaged 744 annually for the Americas, and we can
expect the total to reach about 150,000.
“What trees!…all utterly new to us. Bonpland
keeps telling me he’ll go out of his mind if the
wonders don’tceasesoon.”
—Alexander von Humboldt (1)
Fernández de Oviedo’s chronicles (2) from
1526 contain the first European accounts
of New World plants; they depict huge trees
and include the first reports of tobacco, chili
pepper, and corn, soon to become widely
used throughout the world. Accounts like Ovie do’s
inspired thousands of botanists to explore the
plant riches of the hemisphere over the next five
centuries and to collect over22 millionspecimens,
now housed in the world’sherbaria(3), which pro-
vide the foundation for our current knowledge
(see supplementary text).
The task of naming and classifying plant spe-
cies remains daunting because of the exuberance
of plant diversity in the tropics and the paucity of
comprehensive floristic accounts there. In the
1970s, a new era commenced throughout the
Americas, as collecting and documenting plants
expanded greatly as an activity for in-country
institutions, promoting and strengthening the
capacity of both institutions and individuals. Be-
causeofthelargenumbersofplantspeciesand
the extensive time needed to complete regional
(4,5) or country floras in a region where land
clearing and other human activities were driving
extinction rapidly (6), many botanists turned to
producing online and printed checklists to pro-
vide a better understanding of the plants of indi-
vidual countries or regions. In the 1990s, a series
of country-based plant checklists (7–9)wasorga-
nized by the Missouri Botanical Garden, followed
by other lists produced by institutions through-
out the Americas (10–16). These checklists present
verifiable listings of species based on the analysis
of herbarium specimens, published literature, and
expert knowledge of plant specialists. The task of
preparing authoritative checklists often proved
more difficult than anticipated, in view of the
large amounts of data to be synthesized within
them, and some of the projects took a decade or
more to complete. Checklists are extensively used
as aids to identify plants of an area and are valued
by derivative projects such as Red Lists [e.g., (17)]
and regional lists [e.g., (18)] and as estimates of the
number of threatened species [e.g ., (19)]. In some
countries, they have become the authoritative re-
source for scholars and decision-makers [e.g., (20)].
Between 1993 and 2016, plant checklists were
completed for Mexico (16), the West Indies (14),
and all of South America (7–13,15). Together
with two large ongoing flora projects—Flora of
North America north of Mexico (hereafter North
America) and Flora Mesoamericana, which pub-
lished, in part (4,5), records of the occurrences of
most of their plant species—aseriesofdatasets
became available, making an initial overview of
theplantsoftheAmericaspossible.Herewemerge
these floristic efforts into a single checklist to
present an initial account of the native vascular
plantspeciesknownintheAmericas.Thiscom-
bined working list was produced through a com-
pilation process using the Missouri Botanical
Garden Tropicos database (21).
The total number of native vascular plants
known in the Americas comprises 124,993 species,
6227 genera, and 355 families. This corresponds to
33% of the most recent estimate of 383,671 known
vascular plant species worldwide (22). At a con-
tinental scale, 51,241 species occur on the North
American continent (42,941 endemic) and 82,052
in South America (73,552 endemic), with only
8300 species shared between the two continents.
The vascular plant flora of South America is 6%
larger than the 77,100 species recorded for Africa
(23), which has an area twice its size. Although
Chinahasasurfaceareaofsimilarsizetothe
United States or Canada, its mostly temperate
flora consisting of 30,426 species (24)is97%
larger than the flora of the United States and
Canada combined.
Within the Americas, Brazil has the most di-
verse flora, with 33,161 species, followed by
Colombia (23,104) and Mexico (22,969) (Fig. 1 and
fig. S1A). The most diverse family is Orchidaceae,
with 12,983 species, followed by Asteraceae with
12,043 species and Fabaceae with 7473 (fig. S2A);
24 families have more than 1000 species (figs. S2
and S3A). The largely epiphytic Orchidaceae is
the most diverse family in the tropical Andean
countries, accounting for 9 to 23% of those
countries’floras (Ecuador 23%, Colombia 15%,
Peru 11%, Venezuela 10%, Bolivia 9%); it is also the
most diverse family in Central America (13%) and
the Guianas (9%) and is the second most diverse
in Brazil (8%). By contrast, Asteraceae is the most-
species-rich family in the mostly temperate South-
ern Cone (15%), North America (14%), and Mexico
(13%); this family is second in diversity in most
tropical Andean countries and Central America.
Fabaceae is the most diverse family in Brazil (8%)
and the second most diverse in Mexico (8%), the
Guianas (8%), North America (7%), and Venezuela
(6%). In the West Indies, the most diverse family
is Rubiaceae (7%), which is well represented in all
tropical regions; second in diversity are Orchidaceae
and Asteraceae (table S1). Fifty-two families
are endemic or near endemic to the Americas, in-
cluding the nearlyendemic Berberidopsidaceae,
Bromeliaceae, Cactaceae, Calceolariaceae, Humir-
iaceae, Mitrastemonaceae, and Rapateaceae, with
only one or two species of these families found
on other continents (table S2). Bromeliaceae is
the largest of these families with 3403 species,
39.5% of which are found in Brazil. Five genera
have more than 1000 species in the Americas,
including pantropical Piper (1804) and Peperomia
(1133) and neotropical Epidendrum (1459 species),
RESEARCH
Ulloa Ulloa et al., Science 358, 1614–1617 (2017) 22 December 2017 1of4
1
Missouri Botanical Garden, St. Louis, MO, USA.
2
U.S.
National Herbarium, Smithsonian Institution, Washington,
DC, USA.
3
Herbario Nacional de Bolivia, Universidad Mayor
de San Andrés, La Paz, Bolivia.
4
Instituto de Botánica
Darwinion, Buenos Aires, Argentina.
5
Jardín Botánico del
Quindío, Calarcá, Quindío, Colombia.
6
Department of Ecology
and Evolutionary Biology, University of Michigan, Ann Arbor,
MI, USA.
7
Office of Research, University of Michigan, Ann
Arbor, MI, USA.
8
Departamento de Química y Biología,
Facultad de Ciencias Básicas, Universidad del Norte,
Barranquilla, Colombia.
9
Instituto de Ciencias Naturales,
Universidad Nacional de Colombia, Bogotá, Colombia.
10
Jardim Botânico do Rio de Janeiro, Rio de Janeiro, Brazil.
11
Herbier National, Institut de Systématique Evolution
Biodiversité, Museum National d'Histoire Naturelle, Paris,
France.
12
Herbario Nacional de Venezuela, Instituto
Experimental Jardín Botánico Dr. Tobías Lasser, Universidad
Central de Venezuela, Caraca s, Venezuela.
13
Department of
Geography and the Environment, University of Texas at
Austin, Austin, TX, USA.
14
Museo de Historia Natural, Lima,
Peru.
15
Herbario QCA, Pontificia Universidad Católica del
Ecuador, Quito, Ecuador.
16
Universidad Estatal Amazónica,
Puyo, Ecuador.
17
Departamento de Botánica, Instituto de
Biología, Universidad Nacional Autónoma de México, México
D.F., Mexico.
*Corresponding author. Email: carmen.ulloa@mobot.org
on December 21, 2017 http://science.sciencemag.org/Downloaded from

Miconia (1110), and Lepanthes (1035) (fig. S2B
and table S3). The majority of genera (5975) and
families (223) are represented by fewer than 100
species (fig. S3).
Seventy percent (87,080) of the species in the
Americas are restricted in distribution to one of
the countries or regions (Fig. 2A and fig. S4). In
the West Indies, 67% of the vascular flora is re-
stricted to that region, whereas only 14% of the
flora of the Guianas is endemic there. The tem-
perate North America and Southern Cone also
show high percentages of restricted species (69
and 45%, respectively). At the country level, Brazil
and Mexico have over half of their flora, 55 and
53%, restricted to their borders (fig. S1A). We find,
not surprisingly, that larger areas have more range-
restricted species than smaller ones (fig. S1B).
Neighboring countries of the tropical Andes,
suchasColombia,Ecuador,andPeru,sharea
large number of their species (between 6799 and
9226; table S4). The floristic similarity among
the12areascanbegaugedfromanonmetric
Ulloa Ulloa et al., Science 358, 1614–1617 (2017) 22 December 2017 2of4
Mexico
22,969 (12,069)
West Indies
10,992 (7,378)
Central America
16,335 (5,624) Colombia
23,104 (6,739)
Ecuador
17,548 (5,480)
Peru
19,147 (7,590)
Bolivia
14,431 (2,923 )
Southern Cone
13,125 (5,853)
Brazil
33,161 (18,316)
Guianas
8,271 (1,113)
Venezuela
15,116 (3,359)
North America
15,447 (10,636)
total species (restricted species)
Fig. 1. Map of the Americas showing 12
geographical areas. The areas represent
the 12 data sets used to calculate the
plant-data summary. For each area, the
total number of species of vascular plants
and the number of species restricted to
that area (in parentheses) are shown.
Fig. 2. Contrasting distributions of plant species in the Americas. (A)Meriania aurata, one
of the 87,080 species with restricted distribution, which only occurs in central Ecuador [Photo credit:
L. Jost]. (B)Passiflora foetida, one of the 122 species shared among all 12 geographic areas in
the Americas [Photo credit: O. Hokche].
RESEARCH |REPORT
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mu lti dimensional scaling (Fig. 3). The temperate
Southern Cone has the most commonality with
Brazil and Bolivia. North America shares, by far,
more species with Mexico than with any other
area. The West Indies share species with all 11
areas, but their flora is noticeably less similar to
that of Peru and the Southern Cone. Of the
124,993 native species in the Americas, only 122
species occur in all of the countries and regions
considered here (Fig. 2B and fig. S4).
Our data show that the rate at which plant
names are described and accepted for the
Americas does not show a tendency to level off. In
the past 25 years, between 439 and 1022 (average
744) species have been described each year (Fig. 4).
Five to 10 years after the publication of the Brazil,
Ecuador, and Peru checklists, the number of known
species of plants in those countries increased by
3.6 to 10% (25–28). Brazil is among the four coun-
tries globally that continues to yield the great-
est number of new species described annually (29).
Biologists estimate that as many as 10 to 20% of
species could still remain undescribed in tropical
American biodiversity hotspots (15,30,31). A fore-
cast using linear regression based on the number
of new species described between 1990 and 2014
would yield about 152,000 species by 2050 for the
Americas (fig. S5).
To date, there has been no previous attempt to
catalog the plant diversity of the Americas in its
entirety. Because our checklist is compiled from
specimen-based data from floras and checklists
that cover all sectors of the Americas, it is veri-
fiable and can be readily updated with input from
taxonomic specialists. Keeping these listings up-
to-date is challenging, given the constant stream
of new discoveries and because of taxonomic and
nomenclatural changes. Development of comput-
erized databases has helped to manage informa-
tion, and the use of molecular-based phylogenies
has improved our understanding of taxonomic
and biogeographic relationships. Checklist data
has proven to be a major source of baseline in-
formation for both scientists and governmental
decision-makers, and it helps to fulfill major
goals of the Global Strategy of Plant Conservation
of the United Nation’s Convention on Biological
Diversity (www.cbd.int/gspc/). Such efforts should
assist field-directed and taxonomically oriented
research of plants and their distribution, while there
is still an opportunity for these to be conducted.
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ACKNO WLEDGM ENTS
Our gratitude goes to the hundreds of contributors to the various
projects, collectors, volunteers, and botanical institutions;
governmental and funding agencies; and individuals that have
supported these endeavors. We thank L. Jost for permitting use of
his photograph and S. Tello for preparing Fig. 3. This project was
conceived by C.U.U., P.M.J., and P.H.R. The checklist data were
compiled by C.U.U. and P.M.J., data was contributed by C.U.U.,
P.A.-R., S.B., M.J.B., R.B., P.E.B., L.B., M.C., G.D., R.C.F., S.R.G.,
O.H., B.L., S.L.-Y., D.A.N., M.N., P.H.R., M.T.S., J.L.V., J.L.Z., F.O.Z.,
and P.M.J. The structure of the Tropicos database was developed
by R.E.M. All queries in Microsoft SQL Server and multiple data
reports were conducted by H.S. The project website was designed
Ulloa Ulloa et al., Science 358, 1614–1617 (2017) 22 December 2017 3of4
1.0
0.5
0.0
-0.5
-1.0
Axis 2
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Axis 1
Southern Cone
Bolivia
Brazil
Peru
Ecuador
North America
Mexico
Central America
Colombia
Venezuela
Guianas
West Indies
Fig. 3. Floristic similarity among the 12
geographical areas in the Americas. The
floristic similarity among the geographic areas
represented as a nonmetric multidimensional
scaling (NMDS). Distance and placement is
indicative of similarity among areas. Axes 1 and
2 show the floristic similarities among regions
according to an NMDS ordination based on
Sørensen’s distances.
0
500
1000
1500
2000
2000
1950
1900
1850
1800
1753
0
30000
60000
90000
120000
150000
Year
Number of Species
Cumulative number of species
Fig. 4. Species described per year. The number of plant species (basionyms) described per year
from 1753 to 2015 for the Americas list (blue bars), and the cumulative number of accepted species
(black line).
RESEARCH |REPORT
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by P.M.J. and C.U.U. and populated by H.S. All data analyses
were conducted by and figures and tables prepared by C.U.U. and
P.M.J. The checklist data were formatted by P.M.J. The original
manuscript was drafted by C.U.U., and all coauthors contributed to
subsequent versions. R.C.F. received a Research Productivity
Fellowship from the National Council for Scientific and
Technological Development of Brazil (CNPq). The Checklist of the
Vascular Plants of the Americas is available as a text document in
the supplemental materials, and all of the information is publicly
available on a website on the Missouri Botanical Garden database
Tropicos at http://tropicos.org/Project/VPA.
SUPPLEMENTARY MATERIALS
www.sciencemag.org/content/358/6370/1614/suppl/DC1
Materials and Methods
Supplementary Text
Figs. S1 to S5
Tables S1 to S5
References (32–50)
Data Set S1
14 June 2017; accepted 8 November 2017
10.1126/science.aao0398
Ulloa Ulloa et al., Science 358, 1614–1617 (2017) 22 December 2017 4of4
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An integrated assessment of the vascular plant species of the Americas
Villaseñor, James L. Zarucchi, Fernando O. Zuloaga and Peter M. Jørgensen
León-Yánez, Robert E. Magill, David A. Neill, Michael Nee, Peter H. Raven, Heather Stimmel, Mark T. Strong, José L.
Brako, Marcela Celis, Gerrit Davidse, Rafaela C. Forzza, S. Robbert Gradstein, Omaira Hokche, Blanca León, Susana
Carmen Ulloa Ulloa, Pedro Acevedo-Rodríguez, Stephan Beck, Manuel J. Belgrano, Rodrigo Bernal, Paul E. Berry, Lois
DOI: 10.1126/science.aao0398
(6370), 1614-1617.358Science
, this issue p. 1614; see also p. 1535Science
valuable resource will continue to grow.
relationships between regions. The rate of plant species discovery in the Americas averages almost 750 annually, so this
details of the distribution of species across families and genera, the geographical foci of diversity, and the floristic
about one-third of the worldwide total. They further present−−available, searchable database, includes 124,993 species all known native New World vascular plant species (see the Perspective by Givnish). This compilation, in a publicly
present a comprehensive and integrated compilation of et al.assembled in diverse regional floras and lists. Ulloa Ulloa
Botanical exploration in the Americas has a history that stretches back for half a millennium, with knowledge
The vascular plants of the Americas
ARTICLE TOOLS http://science.sciencemag.org/content/358/6370/1614
MATERIALS
SUPPLEMENTARY http://science.sciencemag.org/content/suppl/2017/12/20/358.6370.1614.DC1
CONTENT
RELATED http://science.sciencemag.org/content/sci/358/6370/1535.full
REFERENCES http://science.sciencemag.org/content/358/6370/1614#BIBL
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