Summary
Background and aims: Hantzschia Grunow is a genus characterized by having valves
asymmetric to the apical axis, markedly dorsiventral, with an eccentric raphe on the
ventral side supported by bulae and ‘hantzschioid’ symmetry of the frustules. In
1942 J. Frenguelli published the ora of diatoms of Neuquén province (Argentina),
work in which he erected Hantzschia subandina as a new species for science. This
work investigates the identity and taxonomic status of this taxon.
M&M: Original material of Hantzschia subandina of the Frenguelli Collection was
analysed with light and scanning electron microscopy.
Results and Conclusions: Observations on the material suggested two different
species were included in the concept of this species assigned originally to the genus
Hantzschia. Furthermore, neither of the two species present are assignable to the
genus Hantzschia. Nitzschia subandina (Frenguelli) comb. nov. has a large central
nodule and a slight asymmetry about the apical axis; it also produces frustules with
nitzschioid and hantzschioid symmetry. We designate a lectotype for this taxon.
In addition, another diatom in the same material with slight asymmetry about the
apical axis has distinctive ornamentation on the mantle of the valve and produces
nitzschioid and hantzschioid frustules. For this taxon we tentatively assign it to the
non-monophyletic genus Nitzschia, describing it as N. araucana sp. nov. We discuss
the possible phylogenetic position of this new taxon, and suggest that the genus
Nitzschia is “the next Navicula” ready to be further subdivided into distinct genera.
Key wordS
Bacillariales, diatoms, Hantzschia, Nitzschia, SEM, systematics, valve morphology
reSumen
Introducción y objetivos: Hantzschia Grunow es un género de diatomeas
caracterizado por la asimetría dorsiventral de sus valvas, rafe soportado por
fíbulas sobre el margen ventral, y simetría hatzschioide de los frústulos. En 1942
J. Frenguelli publicó la ora de diatomeas de la provincia de Neuquén (Argentina),
obra en la que erigió a Hantzschia subandina como una nueva especie para la
ciencia. El objetivo de este trabajo es analizar la identidad de este taxón y su status
taxonómico.
M&M: El material original de Hantzschia subandina, presente en la Colección
Frenguelli depositada en el Herbario de la División Ficología del Museo de La Plata,
fue analizado con microscopías óptica y electrónica de barrido.
Resultados y Conclusiones: la observación del material original de Hantzschia
subandina sugiere que dos entidades distintas fueron incluídas en el concepto
de esta especie. Ambas producen frústulos tanto con simetría nitzschiode como
hantzschioide, por lo que ninguna de ellas pertenece al género Hantzschia.
La primera presenta un nódulo central conspicuo y leve asimetría según el eje
apical; consideramos que estos ejemplares corresponden a Nitzschia subandina
(Frenguelli) comb. nov., y realizamos la enmienda y lectotipicación del taxón. La
segunda entidad presente en el mismo material, posee una leve asimetría según el
eje apical, y una distintiva ornamentación en el manto valvar; hemos asignado este
taxón al género Nitzschia, describiendo N. araucana sp. nov. Discutimos la posible
posición logenética de este nuevo taxón dentro de Nitzschia, género polilético
que requiere de una profunda revisión y subdivisión en géneros, tal como ocurrió
con el género Navicula.
PalabraS clave
Bacillariales, diatomeas, Hantzschia, Nitzschia, MEB, sistemática, morfología valvar
1. Museum of Natural History
and Department of Ecology and
Evolutionary Biology, University of
Colorado, Boulder, CO 80309, USA.
2. División Ficología, Facultad
de Ciencias Naturales y Museo.
Universidad Nacional de La Plata,
(1900) La Plata, Argentina
*Patrick.Kociolek@colorado.edu
Citar este artículo
KOCIOLEK, J. P. & A. A.
VOUILLOUD. 2020. Hantzschia
subandina Frenguelli
(Bacillariophyceae): Morphology,
status and typification, as well as
the description of a new species of
Nitzschia. Bol. Soc. Argent. Bot. 55:
521-534.
DOI: https://doi.
org/10.31055/1851.2372.v55.
n4.29200
John P. Kociolek
1
* & Amelia A. Vouilloud
2
HantzScHia Subandina
Frenguelli (bacillarioPHyceae):
morPHology, StatuS and tyPiFication, aS well aS tHe
deScriPtion oF a new SPecieS oF
nitzScHia
HantzScHia Subandina
Frenguelli (bacillarioPHyceae): morFología,
StatuS y tiPiFicación, aSi como la deScriPción de una nueva eSPecie de
nitzScHia
Recibido: 26 Jun. 2020
Aceptado: 20 Oct. 2020
Publicado en línea: 13 Nov. 2020
Publicado impreso: 20 Dic. 2020
Editora: Luz Allende
ISSN versión impresa 0373-580X
ISSN versión on-line 1851-2372
522
Bol. Soc. Argent. Bot. 55 (4) 2020
introduction
The Bacillariales Ehrenberg is a large order
of diatoms, containing over 3500 taxa (Kociolek
et al., 2020). In terms of number of species,
the order is of approximately the same size as
Mammalia (ca. 6000 taxa; Burgin et al., 2018).
The Bacillariales are characterized by having cells
linear or slightly sigmoid, usually isopolar, with
a bulate raphe in a keel that is usually marginal
(Cox, 2015). The species and subspecic entities
of the Bacillariales are accommodated in less than
30 genera (Kociolek et al., 2020).
Nitzschia Hassall 1845 is the most diverse
genus of this order and contains more than half
of the taxa described within the group. According
to Round et al. (1990) Nitzschia is characterized
by valves symmetrical in outline with respect
to the apical plane, but strongly asymmetric in
structure; eccentric raphe supported by bulae
and ‘nitzschioid’ symmetry of the frustules (the
position of the raphe on one valve is on one
margin, and on the opposite margin on the other
valve of that frustule) or ‘hantzschioid’ symmetry
(the position of the raphe on one valve is on one
margin, and on the same margin on the other
valve of that frustule). There is a high degree of
variability across the species that are included in
the genus, and these have been accommodated into
infrageneric groups and reorganized several times
(Mann, 1986). The type species, N. sigmoidea
(Nitzsch) W. Smith (1853), is characterized by
the presence of a conopeum, which is an external
covering of silica over a portion of the valve face.
Hantzschia Grunow 1877, second but distant in
terms of species diversity within the Bacillariales
(Kociolek et al., 2020), is characterized by
having valves asymmetric to the apical axis,
markedly dorsiventral, with an eccentric raphe
on the ventral side supported by fibulae and
‘hantzschioid’ symmetry of the frustules (Round et
al., 1990). The genus, as typied by H. amphioxys
(Ehrenberg) Grunow (lectotypified by Boyer
1927), has uniseriate or biseriate striae formed
by small, rounded areolae occluded by hymens
(Jahn et al., 2014). There is a complex structure
of the cingulum, that may contain open or closed
elements and with a variable number of porelli
(Round et al., 1990). A recently-described species
assigned to the genus was the rst to include
a conopeum as part of the valve ultrastructure
(Blanco et al., 2019).
The present study was developed in the
framework of a project aimed to revise the type
materials of diatom taxa described by Joaquín
Frenguelli. The diatom collection of Frenguelli
is housed at División Ficología del Museo de
La Plata (Argentina). This work is focused in
Hantzschia subandina Frenguelli, published by
the author in a study of the diatom flora of
Neuquen province, Argentina (Frenguelli, 1942).
Hantzschia subandina has not been cited a
posteriori. Ambiguities between the original
description by Frenguelli and illustrations
provided by him suggest that lectotypication
for H. subandina is required. In addition, another
species included in Frenguelli’s original concept
of H. subandina appears to be new to science, and
we provide a formal description of that taxon.
materialS and metHodS
In this study we analyzed series (sample number
in the Frenguelli Collection) 329 and 427 of the
Frenguelli Collection, corresponding respectively
to periphyton samples of the Covunco River and
Llimen-Có stream, Neuquén. The series 329 has
5 original slides while series 427 has 5 slides
and unmounted material. For light microscopy
(LM) analyses, the slides were observed with a
Leica DM 500 microscope with phase contrast
optics and a Leica DM 2500 with DIC optics and
equipped with a photographic camera Leica DFC
420C (both in La Plata, Argentina). Additional
observations were made with an Olympus BX-51
light microscope with DIC optics equipped with a
BX-71 digital camera (in Boulder, Colorado, USA).
Specimens were located on the slides with an
England Finder
TM
Graticule. For scanning electron
microscopy (SEM) analyses, material from Series
427 was treated with H
2
O
2
, following the procedure
outlined in CEN/TC 230 (2002). Cleaned material
was air-dried onto glass stubs that were sputter-
coated with gold-palladium. SEM observations
were made with a Carl Zeiss NTS SUPRA 40
SEM at the Centro de Microscopías Avanzadas
(CMA), Universidad de Buenos Aires and with a
JEOL JSM-6360LV at the Servicio de Microscopía
Electrónica del Museo de La Plata.
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Bol. Soc. Argent. Bot. 55 (4) 2020
J. P. Kociolek & A. A. Vouilloud - Hantzschia subandina morphology and typication
reSultS
Frenguelli mentioned that Hantzschia subandina
was found as predominant in series 427 and as rare
in series 329. According to this, many specimens
were found in the series 427, and only a few in the
series 329.
In the protologue, the author described his new
species as:
Hantzschia subandina Frenguelli 1942, p. 180,
Plate. 8, gs 26-27 (Fig. 1)
“Frustulis e cingulo visis linearibus, rectis, usque
ad apices subito obtuso-rotundatis marginibus
parallelis, medio subimpressis, 177-248 µ longis
et 11-17 µ latis; valvis 7-8 µ latis, anguste lineari-
lanceolatis, leniter arcuatis, usque ad apices sensim
attenuatis, apicibus valde atenuattis, productis,
porrectis, rostrato-capitatis; punctis carinalibus
parvis, transverse parum prolixis, 9-10 in 10 µ ,
duobus mediis inter. se remotis et pseudonodulo
distincto separatis; striis transversis tenuissimis,
numerosis, circiter 30 et ultra in 10 µ.”
Translated into English, the original description
reads: “Frustule and girdle appear linear with
parallel margins, straight until suddenly at the
apices obtuse-rounded, in the center pinched, 177-
248 µm long and 11-17 µm wide; the valve 7-8
µm wide, narrow, linear-lanceolate slightly arched
becoming attenuated, strongly attenuate at the
apices, produced ends rostrate-capitate. Fibulae
small, transversely short, 9-10/ 10 µm. The two
central bulae separated from one another, the
central nodule distinct. Striae ne, numerous, about
30 or more in 10 µm.”
Initial observations of slides of series 427 show
as predominant specimens with outlines similar to
Frenguelli’s drawings of Hantzschia subandina.
However, more detailed observations show 95% of
the specimens have bulae more or less regularly-
spaced, while only 5 % of the them have the central
bulae widely separated. We never encountered
a specimen with both features. Thus we propose
that the specimens found in the original Frenguelli
material actually correspond to two different
entities. As discussed below, both have specimens
with hantzschioid and nitzschioid symmetries and
therefore cannot belong to the genus Hantzschia
(Round et al., 1990). We consider the species with
separated central bulae (a condition which is
reected in the specimen illustrated by Frenguelli)
(see Fig.1), although less abundant, corresponds
to type of Hantzschia subandina. This species,
however, belongs to the genus Nitzschia. Regarding
the second taxon, it appears to be new to science
and, tentatively, we also assign this species to
Nitzschia. Both species are compared to other
congeners.
Fig. 1. Drawings of Hantzschia subandina
from Frenguelli’s publication.
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Bol. Soc. Argent. Bot. 55 (4) 2020
Nitzschia subandina (Frenguelli) comb. nov.
(Figs 2-3)
Basionym: Hantzschia subandina Frenguelli 1942
(p. 180, Plate, 8, gs 26-27) pro parte.
The metrics herein are based on measurements of
14 specimens in LM and 2 in SEM.
Description
Light Microscope observations (Fig. 2): Valves
slightly sigmoid, tapering to the apices which
terminate with knob-like endings. Frustules exhibiting
both nitzschioid and hantzschioid symmetry (ratio
ca. 2:1). Length 100.0-146.5 µm, breadth 6.0-7.4
µm. Fibulae distinct, 11-13/ 10 µm, the two central
bulae more widely spaced forming a distinct central
nodule. Striae ne, not easily observable in LM,
parallel, indistinctly punctate, 27-30/10 µm. Frustule
quadrangular sligthly concave in the middle in girdle
view. Raphe elevated off the valve face, positioned
to one side.
Scanning Electron Microscope observations (Fig.
3): Externally, linear-lanceolate valves are nearly
straight (Fig. 3A). The raphe is placed on the valve
face, towards one side, in an elevated keel (Fig. 3B-
E). Flat valve surface forming an angle of 90º with
the mantle (Fig. 3 F-H). Uniseriate striae formed by
rounded areolae (Fig. 3C-E, I). Areolae are occluded
Fig. 2. A-J. Nitzschia subandina comb. nov. LM. Specimens of type population. D-F. Lectotypus. Scale bars
= 10 μm (A-G, I-J); 5 μm (H).
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J. P. Kociolek & A. A. Vouilloud - Hantzschia subandina morphology and typication
by distinct hymenes (Fig. 3C). Within a stria, areolae
density is 30-34/ 10 µm. The valve mantle has rows
of areolae similar to the valve surface. The margin
of mantle possesses irregular patterns of silica (Fig.
3J-K). The cingulum is complex, formed by several
open bands. The valvocopula has one row of poroids
occluded by vela; the other cingular elements have
one row of poroids occluded and the pars exterior
possesses irregular patterns of silica similar to the
mantle (Fig. 3I-K).
Fig. 3. Nitzschia subandina, comb. nov. SEM. External views. Specimens of type population. A. Entire
frustule, girdle view. B-C. Center of the valve, showing distinct central nodule. D-E. Valve apices; striae
range from round to ellipsoid in shape; External distal raphe end is evident in E. F-H. Broken valve, showing
the valve surface, forming an angle of 90º with the deep valve mantle and cingulum elements. I-K. Girdle
view, with cingula with a row of round poroids and siliceous markings. J. Detail of junction mantle (right) and
valvocopula (left). K. Detail of cingular bands. Scale bars = 10 μm (A, F); 5 µm (B, D, G-I); 1 μm (C, E, J-K).
526
Bol. Soc. Argent. Bot. 55 (4) 2020
Lectotypus (designated here): Frenguelli
Collection, Slide 427(1), Finder M34/2.
Type Locality: ARGENTINA, Neuquén Province,
Llimen-Có stream, submerged plants. January 21st
1941. J. Frenguelli 427 (Frenguelli Collection).
Since Frenguelli did not designate a holotype,
and indicated two samples in which his species was
found, we have chosen a lectotype for this taxon that
best reects his interpretation of the species in series
427 as indicated in his illustrations of his new taxon
(Fig.1).
Nitzschia subandina can be compared to other,
similarly-sized and -shaped members of Hantzschia
and Nitzschia (Table 1). Frenguelli (1942, p. 180)
compared H. subandina with H. elongata (Hantzsch)
Grunow and Nitzschia vermicularis (Kützing)
Grunow. In his paper Frenguelli pointed out that
H. elongata has valves less lanceolate and more
symmetric outline with flat valve surface and
lower stria and bula densities; the ne structure
reveals more differences in the type and density of
areolae, a raphe externally interrupted in the center
with a longitudinal groove parallel to the raphe and
the mantle margin mantle is smooth. Frenguelli
also suggested that H. subandina can be confused
with Nitzschia vermicularis, particularly in bigger
exemplars; however, this species differs in its lower
bula density. On the other hand, N. vermicularis has
a sigmoid outline in girdle view and always shows a
nitzschioid symmetry.
The species is also compared here with Nitzschia
linearis W. Smith, Hantzschia spectabilis (Ehrenberg)
Hustedt and H. vivacior Lange-Bertalot. N. linearis
is very similar to N. subandina, but has differences in
shape of apices and higher striae density (35-38/ 10
µm versus 27-30/ 10 µm; Kociolek, 2011).
H. spectabilis resembles Nitzschia subandina
when observed with LM, but it differs in its greater
size and by having lower stria and bula densities.
Another taxon with similar appearance when viewed
with LM is Hantzschia vivacior; but this species has
lower stria and bula densities; its ne structure also
shows differences in characteristics of the areolae
and valve mantle; the valve surface is at; internally
it is noted that the bulae have different shape and
size which can be associated with 1-3 virgae.
Nitzschia araucana Vouilloud & Kociolek, sp. nov.
(Figs 4-7)
The metrics herein are based on measurements of
50 specimens in LM and 17 specimens in SEM.
Description
Light Microscope observations (Figs 4): Valves
straight to arched in valve view, linear-lanceolate
Table 1. Comparison of Nitzschia subandina with allied taxa. *measured from of illustrations of the
publication. “nd’ = not determined.
Taxon Reference
Apical
axis (µm)
Transapical
axis (µm)
Fibulae/
10 µm
Striae/
10 µm
Areolae/
10 µm
Nitzschia subandina
(Frenguelli) comb. nov.
This study 100-146.5 6-7.4 11-13 27-30 30-34
Hantzschia subandina
Frenguelli
Frenguelli 1942 177-248 7-8 10 30 aprox. nd
Nitzschia linearis W. Smith Kociolek 2011 60-150 4-6 11-14 35-38 nd
Nitzschia vermicularis
(Kütz.) Hantzsch
Krammer &
Lange-Bertalot
1988
75-250 5 5-7 30-32 nd
Hantzschia elongata
(Hantzsch) Grunow
Lange Bertalot
1993
140-220 14-16 4.5-5.5 13-15 31-35*
Hantzschia spectabilis
(Ehrenberg) Hustedt
Krammer &
Lange-Bertalot
1988
150-500 10-15 4-6 9-12 nd
Hantzschia vivacior
Lange-Bertalot
Lange Bertalot
1993
(60) 90-150 (6.5) 8-11 6-8 13-20 36-42*
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Bol. Soc. Argent. Bot. 55 (4) 2020
J. P. Kociolek & A. A. Vouilloud - Hantzschia subandina morphology and typication
in outline, tapering nearly the entire length of
the valves, with knob-like apices, appearing
asymmetrical to the apical axis, length 113.5-150.0
µm, breadth 5.0-6.4 µm. Frustule quadrangular to
arched to slightly twisted about the apical axis in
girdle view. Frustules exhibiting both hantzschioid
or nitzschioid symmetry. When seen in pairs
(sibling cells), frustules exhibited hantzschioid
+ hantzschioid symmetry or hantzschioid +
nitzschioid symmetry, but never nitzschioid +
nitzschioid symmetry. Raphe elevated off the
valve face, positioned to one side, but extending
onto the valve center at the apices. Fibulae
distinct, 11-14/ 10 µm, small and equidistant along
the length of the valve. Striae uniseriate, parallel,
indistinctly punctate, 24-27/ 10 µm.
Scanning Electron Microscope observations
(Figs 5-7): Valves linear-lanceolate nearly straight,
arched, or twisted (Fig. 5°-C). Externally, raphe
placed in a elevated keel on the valve face,
towards one side but not eccentric, and curves
towards the center of the valve face at the apices
(Fig. 5B, D-J). The valve tapers strongly on one
side, the other side is extended then tapers quickly.
Uniseriate striae formed by rounded areolae which
are individually or in groups bordered by an
elevated rim or extensions oriented perpendicular
to the raphe. These extensions appear to buttress
the elevated keel, and help to give the valve a
rugose appearance (Fig. 5D-E, K-L). Areolae are
occluded by distinct hymenes (Fig. 5 D, K-L).
Within a stria, areolae number 30-34/10 µm. The
valve mantle has rows of areolae similar to the
valve surface (Figs 5L; 7C-D). The margin of the
mantle possesses irregular patterns of silica (Fig.
5L). The cingulum is complex, formed by several
open bands (Fig. 7C-D). The valvocopula has one
or two rows of poroids occluded by vela and pars
exterior with a mbriate margin; the other cingular
elements have several rows of occluded poroids
(Figs 5J, 7).
Internally each bula also serves as an interstria
(Fig. 6A-D, F), leaving one interstria without
a connection between two bulae. Portules of
the canal raphe are nearly round (Fig. 6F-G).
The areolae also appear round and are without
occlusions (Fig. 6D, F). The raphe is continuous
along the length of the valve, terminating at the
apices as small helictoglossae positioned on the
mantle (Fig. 6C, E).
Type Locality: ARGENTINA, Neuquén
Province, Llimen-Có stream, submerged plants.
January 21st 1941. J. Frenguelli 427 (Frenguelli
Collection).
Typification: Holotype (designated here),
Frenguelli Collection Slide 427(2), Finder Q36/2.
Etymology. The specic epithet refers to the
“Araucanos”, an indigenous community of the
Patagonian Andean Region.
Nitzschia araucana can be compared with others
similar taxa such as N. heueriana, N. linearis and
N. tenuis (Table 2)
It is possible that this taxon might be confused
with Nitzschia heueriana Grunow. Fortunately,
the type of N. heufleriana was illustrated by
Lange-Bertalot (1976). The two species are quite
dissimilar from one another in terms of outline,
with N. heueriana having parallel sides and then
tapering close to the apices (see Lange-Bertalot
1976, Fig. 20, which is from Grunow’s type
material). Nitzschia araucana sp. nov. does not
have parallel sides; it tapers from mid-valve to the
apices.
Nitzschia araucana differs from N. linearis in
outline, striae and areolae densities, and central
nodule present (Kociolek, 2011).
Nitzschia araucana can be also compared to
N. tenuis W.Smith, since the type material of this
taxon was studied in Kobayasi & Kobori (1988). N.
tenuis has the same kind of elevated raphe system,
but it differs from the new species in that the central
nodule and raphe are interrupted at the center
and they also have differently-structured cingular
bands.
This second species amongst Hantzschia
subandina pro parte was one that Frenguelli found
to be predominant in series 427 and rare in series
329.
This species exhibited variation in symmetry
about the apical axis, including being asymmetrical
to the apical axis, nearly straight and twisted about
the apical axis. Frenguelli assigned this species
to Hantzschia based in part on his observations
of valves asymmetrical to the apical axis. Our
observations support his description, but they also
suggest the symmetry features of this diatom are
more complex in the types of symmetry present.
In addition, we noted variation in valve
organization amongst frustules and sibling frustules,
with both hantzschioid and nitzschioid symmetries
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Fig. 4. Nitzschia araucana, sp. nov. LM. Specimens of type population. A-B. Holotypus. A-K. Valve views.
K. Higher magnication image of the valve apex; bular and slightly punctate striae are evident. L-R. Girdle
views showing different frustular symmetries. M-N. Two frustules at different levels of focus, one exhibiting
hantzschioid symmetry and one with nitzschioid symmetry. O-P. Frustule at different focal planes, showing
hantzschioid symmetry. Q-R. Two frustules at different levels of focus, one exhibiting hantzschioid symmetry
and one with nitzschioid symmetry. Scale bars = 10 μm (A-J, L-R); 5 μm (K).
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J. P. Kociolek & A. A. Vouilloud - Hantzschia subandina morphology and typication
Fig. 5. Nitzschia araucana, sp. nov. SEM. External views. A. Whole valve, showing linear-elongate shape,
raphe in an elevated keel, knob-like apex and curved nature of the raphe. B. One end of the valve; curved
nature of the raphe system is evident. C. Whole frustules in valve view. D. Central portion of the valve with
elevated raphe and striae in shallow troughs evident. E. Central portion of the valve. Undulate nature of
the valve is shown. F-L. Valve apices showing distal raphe end extending onto the valve mantle. K. High
magnication of the valve showing external occlusions of areolae. L. High magnication of the mantle
showing external occlusions of areolae and irregular patterns of silica on the margin. Scale bars = 10 μm
(A-C); 5 µm (J); 2 μm (D-G, I); 1 µm (H, K-L).
being present. Summarizing the work of Pickett-
Heaps (1983) and Mann (1986), Kociolek &
Williams (1987) detailed how differences in the
migration paths of nuclei during mitosis relative
to the position of keels in the parent valves can
produce true-breeding nitzschioid frustules, true-
breeding hantzschioid frustules or frustules that
can produce both frustules with hantzschioid
and nitzschioid symmetry. Thus, based on these
observations, we assert that the predominant
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Bol. Soc. Argent. Bot. 55 (4) 2020
Fig. 6. Nitzschia araucana, sp. nov. SEM. Internal views. A-B. Valve views, showing evident bulae and
the shift in position of the canal raphe system towards the center of the valve near the apices. Figs C, E.
Apices of the valve, the helictoglossae is positioned on the mantle. D, F. Center of the valve, showing bulae
extending across canal raphe and incomplete, serving as interstriae. G. Valve center showing the raphe is
continuous. H. Transverse section showing the raphe canal. Scale bars = 10 μm (A-B); 5 µm (C-D, H); 1 µm
(E-G).
531
Bol. Soc. Argent. Bot. 55 (4) 2020
J. P. Kociolek & A. A. Vouilloud - Hantzschia subandina morphology and typication
valves in Series 427 of a diatom referred to by
Frenguelli as “H. subandina” without widely-
spaced central bulae is a separate, unique taxon.
Asymmetry about the apical axis of some valves
of “H. subandina” suggests it could belong to
Hantzschia, the original placement of the species by
Frenguelli. However, its ability to produce frustules
both with hantzschioid and nitzschioid symmetry
Fig. 7. Nitzschia araucana, sp. nov. SEM. Girdle views. A-B. Whole frustules. C. Apice in oblique view, note
the keel elevated and the raphe lateral nished in a ssure. D. Apices in girdle view showing the mantle and
the open cingular bands. E-F. Central portion of the valves. G. High magnication view of the girdle region.
All gures show the cingulum elements, being of the open type. Most cingula have a row of poroids. Scale
bars = 10 μm (A-B); 5 µm (C-F); 1 µm (G).
Table 2. Comparison of Nitzschia araucana with allied taxa. *measured from of illustrations of the
publication. “nd” = not determined.
Taxon Reference
Apical
axis (µm)
Transapical
axis (µm)
Fibulae/
10 µm
Striae/
Areolae/
10 µm
10 µm
Nitzschia araucana
sp. nov.
This study 113,5-150 5-6,4 11-14 24-27 30-34
Hantzschia subandina
Frenguelli
Frenguelli 1942 177-248 7-8 10 30 aprox nd
Nitzschia linearis
W. Smith
Kociolek 2011 60-150 4-6 11-14 35-38 nd
Nitzschia tenuis
W.Smith
Kobayasi & Kobori 1988 108-200 4-6 12-13* 28 35-40*
Nitzschia heueriana
Grunow
Kobayasi & Kobori 1988 83 6.3 11-12 22-24 28-30*
Nitzschia vermicularis
(Kütz.) Hantzsch
Krammer & Lange-
Bertalot 1988
75-250 5 5-7 30-32 nd
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Bol. Soc. Argent. Bot. 55 (4) 2020
would preclude it from being placed in Hantzschia.
According to Round et al. (1990, p. 610), “All
Hantzschia spp., however, seem to have a type of
division in which cells of hantzschioid symmetry
always give rise to two daughter cells both of which
have hantzschioid symmetry; this contrasts with the
situation in Nitzschia.” We tentatively include the
species within Nitzschia, even though the genus, as
currently construed, is non-monophyletic (Kim et
al., 2019). If one envisions a narrow circumscription
of the genus Nitzschia, as typied by N. sigmoidea
(Nitzsch) W. Smith, it would contain those species
that have sigmoid valves and a conopeum, features
not found in Nitzschia araucana.
diScuSSion
The exemplars that we observed showed some
remarkable differences in morphological and
morphometric data as compared to the description
offered by Frenguelli. In observations on hundreds
of valves in Frenguelli’s samples, we never
encountered valves that were both dorsiventral
in shape and possessed a wide spacing of bulae
in the centre of the valves (Fig. 1). Differences,
for example, exist in the size ranges between
our observations and the description offered by
Frenguelli (see Table 1). This mis-match between
the reported sizes by Frenguelli and subsequent
measurements is unfortunately a characteristic
common to Frenguelli’s work and has been
previously documented in studies of type materials
of Frenguelli’s taxa (Gorriti et al., 2000; Sala &
Maidana, 2003; Sunesen et al., 2017; Wetzel et
al., 2017; García et al., 2018; Vouilloud et al.,
2018, among others). There does not seem to be
some consistent factor that is common to these
reports (e.g. that all of Frenguelli’s measurements
are 2X the size measured subsequently). It is a
good reminder of the value of looking directly
at specimens in collections, rather than relying
on even primary (let alone secondary or tertiary)
reports of features that might be incorporated into
a table for species comparisons.
We note here that neither of the taxa considered
here have been recorded since Frenguelli (1942)
described Hantzschia subandina. This is a reminder
that there have been few taxonomic studies in the
region. In addition, due to lack of information in
the original publication, we actually know very
little about the ecology of these species. It is hoped
that studies like the present report will stimulate a
review of Frenguelli’s taxa, and the diatom ora of
Neuquén Province.
Nitzschia, with nearly 3,000 named species and
subspecic taxa (Kociolek et al., 2020), might
be considered ‘the next Navicula’, given both the
morphological diversity that has been forced into
this genus (e.g. Krammer & Lange-Bertalot, 1988).
Results of phylogenetic studies which suggest
that the genus is not only non-monophyletic,
but that several other genera are nested within it
(Hantzschia among them) (Witkowski et al., 2015;
Kim et al., 2019) seem to argue for a a more narrow
circumscription of Nitzschia.
The symmetry of Nitzschia araucana sp. nov.
and the structure of its bulae argue for a closer
relationship with Hantzschia, while variable
products of division (hantzschioid + hantzschioid
and hantzschioid + nitzschioid symmetry of
the sibling cells) suggest this species differs
from Hantzschia. Similarities between Nitzschia
araucana sp. nov. and Hantzschia in terms of
asymmetry might suggest this species occupies
a more basal position in the tree of life for the
Bacillariales, within the context of the formal
analysis presented by Witkowski et al. (2015). If
so, the possibility exists that Nitzschia araucana
sp. nov., along with N. alba J.C. Lewin & R.A.
Lewin (Lauritis et al., 1967), N. hierosolymitana
D.G. Mann (formerly H. fenestrata) and N.
sigmoidea (Mann, 1980), are transition taxa
between the primitive condition of true-breeding
Hantzschia taxa and the more derived condition
of true-breeding Nitzschia taxa (Mann’s 1980,
groups 2 and 3) (Witkowski et al., 2015; Kim et al.,
2019). Mann & Trobajo (2014) described species
of Nitzschia that have conopea and hantzschioid
symmetry. The species that are able to produce
frustules with both types of symmetry may not
necessarily represent a natural group, however,
since the morphological features observed in N.
sigmoidea (Mann, 1986; Knattrup et al., 2007), N.
hierosolymitana (Mann, 1980) and N. araucana
reect a broad diversity of valve features in terms
of raphe, fibulae, cingulum organization and
structure, presence or absence of a conopeum,
among others. Further research is required to detail
the phylogenetic relationships of the Bacillariales
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Bol. Soc. Argent. Bot. 55 (4) 2020
J. P. Kociolek & A. A. Vouilloud - Hantzschia subandina morphology and typication
and to align the classication of the order with the
relationships of evolutionary descent. But it seems
clear that the diversity of symmetry, valve features
and patterns of reproduction exhibited by taxa
currently referred to the genus “Nitzschia” argue
for a revision of their classication at the level of
genus and, perhaps, higher levels of taxonomic
hierarchy.
autHor contributionS
Both authors have participated in the data
collection, interpretation and writing of the
manuscript.
acKnowledgmentS
We thank to M. Guiry for his help with
nomenclatural issues and to J.M. Guerrero for his
comments and suggestions which improved this
paper. We appreciate the helpful comments of
two anonymous reviewers. Financial support of
Universidad Nacional de La Plata (grant 11/N856)
is greatly appreciated.
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