Adlafia neoniana (Naviculaceae), a new diatom species from forest streams in Puerto Rico

Abstract

Background and aims – The samples on which this study is based were collected in two streams in Puerto Rico as part of a long-term monitoring program conducted by the National Ecological Observatory Network (NEON). Detailed study of the diatom assemblages revealed the occurrence of a new diatom species belonging to the genus Adlafia. Methods – The study considered 82 samples of epilithic diatoms from two streams in Puerto Rico (Rio Cupeyes and Rio Guilarte) subjected to different degrees of anthropogenic impacts. The new species description is based on high-quality Nomarski (DIC) LM micrographs which document the full spectrum of shape variability along the size diminution series (including girdle views), and SEM images documenting valve ultrastructure (including detailed internal views). In addition we provide information about ecological preferences with respect to trophic state / nutrients, habitat within the stream channel / microhabitat (riffle, run, pool), and season of maximum occurrence. Key results – The new species is described as Adlafia neoniana Cantonati sp. nov. It resembles A. drouetiana but has lanceolate (instead of triundulate) outline, slightly-subcapitate to subrostrate ends (instead of subcapitate to capitate), and higher stria density. It is also similar to A. muscora but differs by elliptic-lanceolate (instead of linear-lanceolate) outline, broader valves, and higher stria density. Moreover, the new species was most abundant in an undisturbed, oligotrophic, shaded forest stream whilst A. drouetiana is known from Brazil to be tolerant to organic pollution and eutrophication. Conclusions – Adlafia neoniana can be differentiated from other similar species in the light microscope by recognizable characters or character combinations. Its discovery and characterization is a contribution to the knowledge of the still understudied biodiversity of microorganisms in tropical streams.

Full text

Plant Ecology and Evolution 152 (2): 378–384, 2019
https://doi.org/10.5091/plecevo.2019.1616
Adlaa neoniana (Naviculaceae), a new diatom species
from forest streams in Puerto Rico
Ionel Ciugulea1, Summyr Burroughs2, Chiara Defrancesco3, Daniel Spitale3,
Donald F. Charles1, Horst Lange-Bertalot4 & Marco Cantonati1,3,*
1Patrick Center for Environmental Research, Academy of Natural Sciences of Drexel University, Philadelphia, PA 19103, USA
2Department of Biodiversity, Earth and Environmental Sciences, Drexel University, Philadelphia, PA 19104, USA
3MUSE - Museo delle Scienze, Limnology & Phycology Section, Corso del Lavoro e della Scienza 3, I-38123 Trento, Italy
4Goethe Universität Frankfurt, Biologicum, Max-von-Laue Straβe 13, 60438 Frankfurt, Germany
*Author for correspondence: marco.cantonati@muse.it
SHORT COMMUNICATION
Background and aims – The samples on which this study is based were collected in two streams in
Puerto Rico as part of a long-term monitoring program conducted by the National Ecological Observatory
Network (NEON). Detailed study of the diatom assemblages revealed the occurrence of a new diatom
species belonging to the genus Adlaa.
Methods – The study considered 82 samples of epilithic diatoms from two streams in Puerto Rico (Rio
Cupeyes and Rio Guilarte) subjected to dierent degrees of anthropogenic impacts. The new species
description is based on high-quality Nomarski (DIC) LM micrographs which document the full spectrum of
shape variability along the size diminution series (including girdle views), and SEM images documenting
valve ultrastructure (including detailed internal views). In addition we provide information about ecological
preferences with respect to trophic state / nutrients, habitat within the stream channel / microhabitat (rie,
run, pool), and season of maximum occurrence.
Key results – The new species is described as Adlaa neoniana Cantonati sp. nov. It resembles A. drouetiana
but has lanceolate (instead of triundulate) outline, slightly-subcapitate to subrostrate ends (instead of
subcapitate to capitate), and higher stria density. It is also similar to A. muscora but diers by elliptic-
lanceolate (instead of linear-lanceolate) outline, broader valves, and higher stria density. Moreover, the
new species was most abundant in an undisturbed, oligotrophic, shaded forest stream whilst A. drouetiana
is known from Brazil to be tolerant to organic pollution and eutrophication.
Conclusions – Adlaa neoniana can be dierentiated from other similar species in the light microscope by
recognizable characters or character combinations. Its discovery and characterization is a contribution to
the knowledge of the still understudied biodiversity of microorganisms in tropical streams.
Key words – Tropical diatoms, Adlaa, Adlaa neoniana, Adlaa drouetiana, Adlaa muscora,
morphology, new species, ecology, streams, Puerto Rico.
© 2019 The Authors. This article is published and distributed in Open Access under the terms of the Creative Commons Attribution
License (CC BY 4.0), which permits use, distribution, and reproduction in any medium, provided the original work (author and source)
is properly cited.
Plant Ecology and Evolution is published by Meise Botanic Garden and Royal Botanical Society of Belgium
ISSN: 2032-3913 (print) – 2032-3921 (online)
INTRODUCTION
Adlaa Lange-Bert. (in Moser et al. 1998) is a relatively
small (26 species listed in DiatomBase, Kociolek et al. 2018)
freshwater, isovalvar, isopolar, bilaterally symmetrical (“na-
viculoid”) genus (Jüttner et al. 2018). According to Lange-
Bertalot (in Moser et al. 1998) and Lange-Bertalot (2001),
the genus typically includes small species (< 25 µm); cells
are solitary, with linear to linear-lanceolate outline, and
rostrate, subcapitate, or wedge-shaped ends; the raphe is
liform, with at most slightly-expanded central pores, and

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Ciugulea et al., New Adlaa species from Puerto Rico
terminal ssures strongly curved unilaterally (Cantonati et
al. 2017); the axial area is very narrow, the central area is
variable but never reaching the margins; the dense striae are
radiate in the central part, becoming abruptly convergent to-
wards the ends; under the SEM, the uniseriate striae proceed
uninterrupted from the valve face to the mantle, the areolae
are closed by hymenes outside, and the narrow girdle of each
theca is formed by two copulae, each with a biseriate row of
poroids; the genus is named after the Association of French
Speaking Diatomists (ADLAF - Association des Diatomistes
de LAngue Française).
Some species are widely distributed, and apparently
cosmopolitan, e.g. Adlaa bryophila (J.B.Petersen) Gerd
Moser, Lange-Bert. & Metzeltin (e.g. Metzeltin & Lange-
Bertalot 1998, Cantonati et al. 2017, Tusset et al. 2017). Ad-
laa drouetiana (R.M.Patrick) Metzeltin & Lange-Bert. is so
far known only from Brazilian streams (Tusset et al. 2017).
Adlaa sinensis Bing Liu et D.M.Williams was described
from China (Liu et al. 2017) but was recently found in Brazil
(Tusset et al. 2017).
With respect to their ecology, many Adlaa species are
considered pseudoaerial (e.g. Spaulding & Edlund 2009),
and typically colonize alkaline, oligotrophic, headwater
streams (e.g. Spaulding & Edlund 2009, Liu et al. 2017, Tus-
set et al. 2017). However, they are also found over a wide
range of electrolyte content (e.g. Adlaa lange-bertalotii
occurring in fairly low to intermediate mineralization lev-
els; Monnier et al. 2012). A few taxa colonize environments
with higher trophic state (e.g. Adlaa minuscula var. muralis
(Grunow) Lange-Bert. (in Lange-Bertalot & Genkal 1999)
which is tolerant of organic pollution up to the transition be-
tween α-mesosaprobic and polysaprobic conditions and typi-
cal of running waters with high concentrations of nutrients;
Cantonati et al. 2017).
Other new species of Adlaa were described recently, in
particular from streams in Brazil (Tusset et al. 2017), China
(Liu et al. 2017), central Europe (Grand-Duchy of Luxem-
bourg, Monnier et al. 2012), the United States (Morales &
Le 2005), and Lake Baikal (Russia, Kulikovskiy et al. 2012).
Adlaa drouetiana was described, as Navicula Droueti-
ana, by Ruth Patrick in 1944. In 1998 Ditmar Metzeltin and
Horst Lange-Bertalot provided the rst SEM image. For
many years, well-documented reports remained scarce, and
only recently have new data on its morphology (Tusset et al.
2017) and ecology (Heinrich et al. 2014) been published.
The aim of the present paper is to describe and character-
ize a new Adlaa species found in two streams in SW Puerto
Rico subjected to dierent degrees of anthropogenic impacts.
Sample material and ecological data for this study are from
the USA National Ecological Observatory Network (NEON)
program, which regularly surveys the streams. The species
description is based on high-quality Nomarski (DIC) LM
micrographs of the full spectrum of shape variability along
the size diminution series (including girdle views), and SEM
images documenting valve ultrastructure (including detailed
internal views). In addition we provide ecological data on
trophic state / nutrients, within-stream habitat character / mi-
crohabitat (rie, run, pool), and season of maximum occur-
rence.
Parameters Cupeyes Guilarte
Longitude 66°59′12.30″W 66°47′54.73″W
Latitude 18°06′48.65″N 18°10′26.77″N
Elevation (m a.s.l.) 166 548
Discharge (l/s) 23.1–658.1, 151.3 (29) 72.2, 688.6, 230.1 (25)
Temp. (ºC) 21.3–25.0, 23.2 (45) 12.9–22.8, 20.6 (40)
Dissolved oxygen (%) 87–100, 94 (23) 9–107, 94 (21)
pH 7.80–8.30, 8.08 (12) 7.47–7.92, 7.76 (11)
Conductivity (µS.cm–1) 204–400, 271 (12) 125–286, 202 (11)
Alkalinity (meq/l) 1.90–3.75, 2.63 (45) 1.04–2.34, 1.71 (39)
Nitrate + Nitrite N (µg/l) 240–348, 290 (12) 380–613, 493 (11)
Total Dissolved N (µg/l) 126–436, 352 (12) 458–704, 583 (11)
Total Dissolved P (µg/l) 0–9, 2 (12) 1–65, 19 (11)
Silica (mg/l) 0.01–19.99, 14.50 (12) 0.01–15.30, 10.56 (11)
Sulphate (mg/l) 0.53–4.12, 2.80 (12) 1.52–5.61, 4.67 (11)
Chlorine (mg/l) 1.72–10.08, 5.71 (12) 0.45–7.29, 5.56 (11)
Calcium (mg/l) 2.65–6.23, 4.09 (12) 15.12–33.10, 25.55 (11)
Magnesium (mg/l) 21.74–42.08, 31.53 (12) 3.16–6.92, 5.50 (11)
Table 1 – Location, physical and hydrochemical characteristics of the two study streams.
min-max, average (in bold), and N (= total number of available data points). All data available for the study period (2015–2016) were
downloaded from https://www.neonscience.org/.

380
Pl. Ecol. Evol. 152 (2), 2019
MATERIAL AND METHODS
Study streams
The two tropical streams studied in southwest Puerto Rico
have low-to-medium discharge, warm water, and medium
conductivity (table 1). They are part of NEON (National
Ecological Observatory Network) Domain D04, Atlantic
Neotropical.
The Rio Cupeyes study site (NEON code: CUPE; Acad-
emy of Natural Sciences site code: NFS008, site_id: 207563;
nearest city: San German, Puerto Rico, PR, USA) is in the
Maricao State Forest and is a NEON aquatic core eld site.
The Site Host is the Commonwealth of Puerto Rico. The li-
thology is serpentinite rocks (Cretaceous). The area is made
up of old and second-growth tropical, moist and wet forest.
It is considered a good example of an increasingly rare in-
tact Puerto Rican stream (https://www.neonscience.org/eld-
sites/eld-sites-map/CUPE). Average total dissolved phos-
phorus (TDP) is 2 µg/l, and average total dissolved nitrogen
(TDN) is 352 µg/l. The average magnesium concentration
(31.53 mg/l) is high (table 1).
The Rio Guilarte study site (NEON code: GUIL; Acad-
emy of Natural Sciences site code: NFS009, site_id: 207564;
nearest city: Adjuntas, Puerto Rico, PR, USA) is a relocatable
(= may be re-deployed periodically throughout the 30-year
lifetime of the Observatory) NEON aquatic eld site. The
Site Host is the University of Puerto Rico. The lithology is
characterized by the Anon formation: interbedded andesite/
volcanic brecia, rhyodacite, and sandstone/siltstone of the
Upper Eocene (https://www.neonscience.org/eld-sites/eld-
sites-map/GUIL). Average TDP is 19 µg/l, and average TDN
is 583 µg/l (table 1).
Slides studied, microscopy, new species description
The samples on which this study is based were taken at the
CUPE and GUIL sites from 20 Jan. 2015 to 20 Dec. 2016 and
from 22 Jan. 2015 to 29 Nov. 2016, respectively. All sample
information and diatom counts can be downloaded from the
NEON Data Portal: http://data.neonscience.org/home. In the
counts, the new species described here was called A. droue-
tiana, as counts were carried out before the new species was
recognized.
Eighty-two epilithon samples from the Cupeyes (37 sam-
ples) and Guilarte (45 samples) streams, collected on 11 sam-
pling dates, were studied. On each sampling date, a primary
(5 composite samples) and, usually but not always, a second-
ary (3 samples) habitat were sampled. Primary habitat was
rie in both streams. Secondary habitat was run in Cupeyes
and pool in Guilarte. The sampling stations are long stream
reaches (1 km); rie (and run and pool) samples are taken
along this stretch. Three cobbles for each composite sample
were collected randomly. A halved 35-mm slide cassette was
used as template to delineate sampling area. Periphyton was
scraped from the cobbles with a brush (Parker 2018).
Samples were digested following the NAWQA protocols
(Charles et al. 2002). The cleaned material was mounted in
Naphrax (refractive index of 1.74). At least 600 valves were
identied and counted using a Zeiss Ser. N. 800392 (Zeiss,
Species Adlaa neoniana Adlaa drouetiana Adlaa muscora
Source of
information /
character
This paper Tusset et al. (2017) Patrick (1944) Kociolek & Reviers
(1996) Lange-Bertalot (2001) Tusset et al. (2017)
Valve length (µm) 9.4–18.5, 14.5, n = 51 14.7–20.3 17.4 19.5 13.6–18.7* 10–17.6
Valve width (µm) 3.7–5.1, 4.2, n = 51 4.0–5.4 4 3.5 3–4* 3.1–4.6
Valve shape elliptic-lanceolate
linear-lanceolate
typically slightly
triundulate
linear to lanceolate elliptic-lanceolate linear-lanceolate* elliptic-lanceolate
Apex rostrate to subcapitate capitate to subcapitate rostrate subrostrate rostrate to
subrostrate* rostrate to subcapitate
Striae (in 10 µm) 30–32, 32, n = 77 22–28 29–30 23–26 – 28–32
Distance between
central raphe ends
(µm)
0.5–1.2, 0.7, n = 51 0.6–1.2, 0.9,* n = 10 – – 0.6–0.7, 0.6,* n = 5 0.7–1.2, 0.9,* n = 9
Areolae (in 10 µm) 45–50 30–50 – – – 50–62
Table 2 – Morphometric characteristics of Adlaa neoniana Cantonati sp. nov., and comparison with the most similar species, Adlaa drouetiana and A. muscora.
When available, min-max, average, and total number of observations are provided (averages are in bold). For the stria density, the mode is provided instead of average.

381
Ciugulea et al., New Adlaa species from Puerto Rico
Jena, Germany) and x1000 magnication (ANSP Drexel
PCER Procedure No. P-13-39 Revision 2 02/17). High-
quality Nomarski (DIC) LM micrographs were taken using
a ANSP microscope Zeiss Akioskop 50 with objective lens
Zeiss Plan-Apochromat 100x/1.40 Oil and digital camera
Nikon Digital Sight DS Fi1.
Materials (slides, prepared material, and aliquots of the
original samples), including the holotype slide, are held at
the ANSP Diatom Herbarium (ANSP). Isotype slides and ali-
quots of prepared material from the same locality and sub-
stratum are being deposited in the NEON Biorepository in
Arizona, the Diatom Collection of the Natural History Muse-
um (BM) of London (UK), and the Diatom collection of the
MUSE - Museo delle Scienze (TR), Trento, Italy. Numbers
of specimens measured along the size diminution gradient
to obtain ranges and averages (mode) of morphological and
ultrastructural features are indicated in table 2. Stria density
was assessed on both sides of the same valve in 26 cases out
of 51, for a total of 77 measurements.
SEM observations were made primarily at the University
of Frankfurt using a Hitachi S-4500 (Hitachi Ltd., Tokyo, Ja-
pan) at high vacuum on gold coated stubs. Terminology for
valve morphology is based on Round et al. (1990) and Lange-
Bertalot (2001).
Statistical analyses
The ecological preferences of Adlaa neoniana were stud-
ied assessing three factors: river (Cupeyes, Guilarte; df = 1),
habitat (rie, run, pool; df = 2), and season (autumn, winter,
and summer; df = 2) . Since the variance was heterogeneous
(Bartlett’s K-squared = 6.67, df = 1, p-value < 0.01), the three
factors were tested separately using a non-parametric statis-
tic. The Kruskal–Wallis test was used instead of the one-way
analysis of variance (ANOVA). Since it is a non-parametric
method, the Kruskal–Wallis test does not assume a normal
distribution of the residuals, and is often used in the case of
dierent sample sizes (Sokal & Rohlf 1995). All the analyses
were carried out using R (R Core Team 2018).
RESULTS
Adlaa neoniana Cantonati, sp. nov.
Figs 1–2
Type material – Unites States of America, Puerto Rico,
Cupeyes Stream, National Forest, south-eastern part of the
Island of Puerto Rico, lithology: serpentinites (metamorphic
rocks), (18°06′48.65″N, 66°59′12.30″W, 166 m a.s.l.), 19
Feb. 2015 (holo-: ANSP, slide NEON00323 b, partly shown
Figure 1 – Adlaa neoniana, LM size diminution series from the type locality. Note the rostrate to subcapitate ends and a considerable
reduction in cell size: A–AD, valve views; AE–AF, girdle views (the same specimen is shown in two dierent focal planes). Scale bar =
10 µm.

382
Pl. Ecol. Evol. 152 (2), 2019
here in g. 1; iso-: BM, slide BM-101962; iso-: TR, slide
cLIM004 DIAT 3514; iso-: NEON Biorepository, Arizona
State University’s Natural History Collection in Tempe, AZ,
slide NEON00323 a).
Registration – http://phycobank.org/101113
Description: LM – Frustules narrowly rectangular in girdle
view; frustule width slightly less than 2 µm (g. 1AE & AF).
Valves elliptic-lanceolate with rostrate to subcapitate apices
(g. 1A–AD). Valve length 9.4–18.5 µm, valve width 3.7–
5.1 µm. Axial area narrow linear along the entire length of
the valve, central area indistinct. Proximal raphe ends clear-
ly discernible with LM, straight and slight widened. Striae
dense, discernible only with good quality optics, 30–32 in 10
µm, radiate, becoming convergent towards the apices.
Description: SEM – Axial area slightly widening towards
central area (g. 2A & B). Raphe with external terminal s-
sures hooked towards the secondary side; central raphe ends
very slightly bent towards the primary side (g. 2A & B).
Striae uniseriate, radiate, becoming abruptly convergent near
the valve ends, Striae continuing onto the mantle without in-
terruption (g. 2A). A few shortened striae present on each
side of the central part of the valve (g. 2A & B). Areolae
rounded to rectangular, occluded by hymenes outside (g.
2D & E). Internally, both proximal raphe ends deected to-
wards the primary side (g. 2C & D), distal raphe ends ter-
minating in small helictoglossae (g. 2E & F).
Etymology – The new species is named after the NEON
(National Ecological Observatory Network) programme.
This is a 30+ year project dedicated to understanding how
environmental change (including climate change) impacts
ecosystems at the study sites. It includes > 80 sites from 20
eco-climatic domains representing US ecosystems: Hawaii,
Alaska, the continental Unites States, and Puerto Rico. All
the materials studied for the present paper were provided by
NEON.
Similar taxa – The most similar species is Adlaa droueti-
ana, which has triundulate margins and a lower stria density
(22–28 in 10 µm; table 2). Adlaa sinensis is also similar, but
is typically smaller, and has striae which cannot be counted
in LM (32–36 in 10 µm).
Distribution – The wider distribution is not yet known be-
cause the species has not been distinguished previously from
other Adlaa taxa. So far it is known only from the type lo-
cality (Rio Cupeyes) and from another stream in Puerto Rico
(Rio Guilarte), located 21 km away. It is, however, possible
that the the populations from Brazil identied by Tusset et al.
(2017) as A. muscora also belong to Adlaa neoniana, hence
it might also occur in several streams and rivers in Brazil.
Adlaa neoniana occurred in 25 out of the 37 samples
analyzed from Rio Cupeyes, and in 13 out of the 45 samples
from Rio Guilarte. Maximum relative abundance was higher
in Rio Cupeyes (6.4%) compared to Rio Guilarte (0.65%).
Only epilithon samples were available for this study but
they were collected from dierent habitats and stream reach-
es (within the same station). Figure 37 shows the distribu-
tion of the species with respect to stream, microhabitat, and
season, showing that it was clearly more abundant and fre-
quent in Rio Cupeyes (Kruskal-Wallis chi-squared “streams”
= 15.35, d.f. = 1, p < 0.0001). A hypothesized preference for
ries and runs was not statistically signicant (Kruskal-Wal-
Figure 2 – Adlaa neoniana, SEM: A & B, external views; C–F, internal views. Scale bars: A = 3 µm; B & C = 2 µm; D–F = 1 µm.

383
Ciugulea et al., New Adlaa species from Puerto Rico
lis chi-squared = 5.43, d.f. = 2, p = 0.07), or a higher abun-
dance in winter (February) or summer (July) (Kruskal-Wallis
chi-squared = 0.42, d.f. = 2, p = 0.81).
Ecology and co-occurring diatom species – The Rio Cupe-
yes is a shaded, Puerto Rican forest stream of high ecologi-
cal quality with low to medium discharge and conductivity.
This stream diers from the impacted (agriculture in the sur-
roundings) Rio Guilarte, in which the new species was much
less abundant, mainly by having lower TDN and TDP values,
consistently high oxygen concentrations (% saturation can,
on the contrary, drop down to 9% in the Rio Guilarte), and
six times higher magnesium concentrations due to the special
lithology – serpentinites – of the Rio Cupeyes) (table 1).
The dominant diatom species of the most common gen-
era at the type locality were (species in the Guilarte stream
are shown in brackets): Achnanthidium jackii Rabenh. [A.
eutrophilum (Lange-Bert. in Lange-Bertalot & Metzeltin)
Lange-Bert.], Gomphonema sp. 1 NEON Puerto Rico MC
unpublished [G. kobayasii Kociolek & Kingston], Navicula
parablis M.H.Hohn & Hellerman [N. simulata Manguin],
Nitzschia paleacea Grunow in Van Heurck [Nitzschia cf.
palea], Ulnaria lanceolata (Kütz.) Compère [Ulnaria mono-
dii (Guermeur) Cantonati & Lange-Bert. + Ulnaria ramesii
(Hérib.) T.Ohtsuka].
DISCUSSION
The established species most similar to our proposed new
species Adlaa neoniana is Adlaa drouetiana, which, how-
ever, has: – lower stria density (22–28 in 10 µm vs. 30–32 in
10 µm, with 32 in 10 µm being the mode for Adlaa neoni-
ana; table 2); – typically a triundulate outline, as compared
to a lanceolate outline in A. neoniana; – subcapitate to capi-
tate ends vs. slightly-subcapitate to subrostrate ends in small-
er specimens of A. neoniana; – larger dimensions, in particu-
lar length: 15–20 µm vs. 9–18 µm for A. neoniana (table 2);
– typically lower areola density: 30–50 in 10 µm vs. 45–50
in 10 µm for A. neoniana; – a high tolerance to organic pol-
lution and eutrophication, as shown in subtropical temperate
Figure 3 – Relative abundance (%) of Adlaa neoniana in the two
streams, in the dierent habitats, and in the dierent seasons (A =
Autumn, W = Winter, and S = Summer).
streams (Lobo et al. 2004, as Adlaa bryophila, 2010) and
headwaters (Heinrich et al. 2014) in Brazil.
Since Adlaa neoniana was most abundant in the stream
on serpentinite rocks, which in Puerto Rico occurs only in
the area where the Rio Cupeyes (= type locality of A. neo-
niana) is located (Torres & Quiñones 2003), it might have
a preference for increased magnesium concentrations, which
is not known for A. drouetiana. Preference for higher mag-
nesium contents has been reported in the literature for other
diatom species (e.g. Achnanthidum dolomiticum Cantonati &
Lange-Bert.; Cantonati & Lange-Bertalot 2006, Cantonati et
al. 2017).
Other similar species are Adlaa sinensis and Adlaa
multnomahii E.Morales & Le that are typically smaller, and
have striae which are uncountable with LM, and Adlaa
bryophila which is narrower (2.5–4 µm) (e.g. Cantonati et
al. 2017).
As concerns Adlaa muscora (Kociolek & Reviers)
Lange-Bert. in Moser et al. (1998), we think that in the re-
cent publication by Tusset et al. (2017) there might have
been some taxonomic drift from the original concept. This
is likely to have been caused by the fact that gures in Mo-
ser et al. (1998: pl. 6, gs 3–8) display ample morphological
variability for Adlaa muscora, and these gures are likely
to include more than one species. For this reason, we used
Lange-Bertalot (2001), instead of Moser et al. (1998), as one
of the references for A. muscora in table 2.
If only LM micrographs taken from the type slide (i.e.
Moser et al. 1998: pl. 6, gs 7 & 8) are considered, it appears
clear that the original taxonomic concept for this species re-
fers to linear-lanceolate forms with comparatively low width
and stria density (23–26 in 10 µm; Kociolek & Reviers 1996:
table 2). If this original concept is kept in mind, Lange-Ber-
talot’s (2001) concern that Adlaa muscora is dicult to dis-
tinguish from A. bryophila appears to be well justied.
Considering the original taxonomic concept for A.
muscora discussed above, comparing the morphometric data
in table 2, and carefully examining the micrographs and data
provided in Tusset et al. (2017) for A. muscora, we conclude:
(1) our proposed new species diers from A. muscora mainly
because it has an elliptic-lanceolate (instead of linear-lanceo-
late) outline, broader valves, and higher stria density; (2) the
population from Brazil identied by Tusset et al. (2017) as A.
muscora does not belong to this species but likely represents
a Brazilian population of Adlaa neoniana.
Adlaa neoniana can thus be dierentiated from other
similar species by recognizable characters or character com-
binations. Its discovery and characterization is a contribu-
tion to the knowledge of the still understudied biodiversity
of tropical stream microorganisms (compare Jyrkänkallio-
Mikkola et al. 2018).
ACKNOWLEDGMENTS
The National Ecological Observatory Network is a program
sponsored by the National Science Foundation and operated
under cooperative agreement by Battelle Memorial Institute.
This material is based in part upon work supported by the
National Science Foundation through the NEON Program.

384
Pl. Ecol. Evol. 152 (2), 2019
Academy of Natural Sciences Diatom Herbarium. Kathryn
Longwill of the ANSP Patrick Center prepared the micro-
scope slides and helped manage sample material. M. Canto-
nati is grateful to MUSE for allowing him to write this paper
as part of the MUSE research theme on the diatoms from
tropical freshwater habitats.
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Managing Editor: Ingrid Jüttner
Submission date: 4 Dec. 2018
Acceptance date: 13 Mar. 2019