Bull. Natl. Mus. Nat. Sci., Ser. B, 46(2), pp. 65–73, May 22, 2020

Transfer of the Gomphoneis tetrastigmata Species Complex
and Related Taxa to the Genus Gomphonella (Bacillariophyceae)
Akihiro Tuji
Department of Botany, National Museum of Nature and Science,
4–1–1 Amakubo, Tsukuba, Ibaraki 305–0005 Japan
E-mail: tuji@kahaku.go.jp(Received 13 February 2020; accepted 25 March 2020)

Abstract Since the Gomphoneis tetrastigmata species complex, which has four stigmata, including G. okunoi and G. pseudookunoi described by Tuji (2005), both from Japan, shares morphological characteristics with Gomphonella olivacea except in having four stigmata, and belong to thesame clade in the phylogenetic trees based on rbcL and 18S rRNA. Thus, these taxa and related
taxa are transferred to the genus Gomphonella.
Key words : Gomphoneis, Gomphonella, Gomphonema, new combination.

Introduction

Materials and Methods

Jahn et al. (2019) presented the phylogenetic
position of a well-known taxon, Gomphoneis olivacea (Hornem.) P.A.Dawson ex R.Ross etP.A.Sims, and transferred it and related taxa tothe genus Gomphonella Rabenh. 1853, because
the clade with this taxon and related taxa is separated from the clades of the genera Gomphonema
and Gomphoneis. The Gomphoneis tetrastigmata(Horik. et Okuno) Ohtsuka species complex(Tuji, 2005), especially G. okunoi Tuji, is common in Japanese rivers and lakes (Tuji, 1995;
Watanabe et al., 2005). The morphological characteristics of this species complex are very close
to those of Gomphonella olivacea (Hornem.)
Rabenh. except for having four stigmata. In thispaper, I present the phylogenetic trees for Gomphoneis okunoi with Gomphonella olivacea,Gomphoneis taxa, and Gomphonema taxa, anddiscuss the taxonomical treatment of the Gomphoneis tetrastigmata species complex.

A ﬁeld sample, TNS-AL-56464 housed inTNS (Department of Botany, National Museumof Nature and Science), was collected from arope in the lake water at Chikubu Island, Lake
Biwa, on 19 March 2008 by A. Tuji. The strain
Ak513 was isolated from this ﬁeld sample using
agar plates [1% agar with d medium: modiﬁed
WC medium described by Tuji (2000)]. Thisstrain died. DNA was extracted using this strain
by the cetyl trimethylammonium bromide(CTAB) method with glass beads, followed bypolymerase chain reaction ampliﬁcation (PCR)
and phylogenetic reconstruction (Tuji et al.,2014). The obtained sequences were deposited tothe genebank (LC530727 for rRNA andLC530728 for rbcL).
For morphological examinations, the following ﬁeld samples were examined.
1. Material numbered TNS-AL-54241c inTNS, collected from the Arakawa River by A.
Tuji on 25 November, 2004. This is an isotype
for Gomphoneis okunoi described in Tuji (2005).
2. Material numbered TNS-AL-TW-1331cfrom T. Watanabe collection in TNS collected© 2020 National Museum of Nature and Science

66Akihiro Tujifrom Tikubu-shima, Lake Biwa (Sample No:C2), by T. Watanabe on 4 July, 1988. This is an
isotype for Gomphoneis pseudookunoi Tujidescribed in Tuji (2005).
3. Material numbered TNS-AL-TW-6274cfrom T. Watanabe collection in TNS collectedfrom the northern part of Minae, Lake Shikotsu,
by T. Watanabe on 24 June, 1990. This sample
was examined for Gomphoneis tetrastigmata inTuji (2005).
4. Material numbered TNS-AL-TW-11527c T.
Watanabe collection in TNS collected from theSeine River, France, by T. Watanabe on 20 June,1992. Gomphonella olivaceum is common in thissample.
Results and Discussion
Phylogeny
The phylogenetic trees of Gomphoneis okunoi
and related taxa determined using rbcL and 18SrRNA are presented in Figs. 1 and 2. G. okunoi(strain Ak513) is positioned at the anchor of thegenus Gomphonella clade and separated from theclades of other genera including Gomphonema
and Gomphoneis. Gomphoneis okunoi and theGomphonella clade are monophyly, and no othergenus is positioned. The supporting values
between Gomphoneis okunoi and genus Gomphonella were 93 for rbcL and under 70 for 18S
rRNA using maximum likelihood analysis. The
low supporting values might be caused by therelatively short sequences of genus Gomphonella
deposited by Jahn et al. (2019). The molecular
information in Jahn et al. (2019) clariﬁed that theGomphonella taxa belong to the Cymbellales but
not to the Gomphonemataceae. Gomphoneis okunoi should also belong to the Cymbellales, andshould not belong to the genus Gomphonema orGomphoneis, both of which are members ofGomphonemataceae.
Morphological analysis
The Gomphoneis tetrastigmata species complex, including G. okunoi and G. pseudookunoi,
has an outline very close to that of Gomphonella

olivacea. This species complex and Gomphonella olivacea share the following features.
The valves are wedge-shaped in valve view andsymmetric to the apical axis. Pseudoseptae arepresent (Fig. 3). A longitudinal line is not present. The striae at the central area are reduced inlength and make a butterﬂy-like central area
(Figs. 4, 5, 7). The striae are biseriate (Figs. 3–7).
Striae in the headpole are always biseriate (Figs.
3, 6). The areolae are small and rounded and not
occluded by siliceous ﬂaps (Figs. 3–7). An apicalpore ﬁeld (composed of porelli) exists at thefootpole and is bisected by a terminal ﬁssure(Figs. 3, 6). The porelli make a single row at thefootpole (Fig. 6). The important difference
between this species complex and Gomphonella
olivacea, is the existence of stigmata (Figs. 4, 7).
These Gomphoneis taxa have four stigmata(Figs. 7 B–D), but Gomphonella olivacea does
not have any stigmata (Fig. 7A). The lack of stigmata is an important characteristic in theemended description of genus Gomphonella byJahn et al. (2019). The external openings of thestigmata are round and are positioned in the central area (Fig. 7). The internal openings of thestigmata of this species complex are complex
like in the stigmata of genus Cymbella or Didymosphenia (Fig. 4); however, the internal openings of G. tetrastigmatum are sometimes notobserved (Fig. 5), and/or they are sometimes
observed only for some of the four stigmata (Fig.
4D). The genus Gomphosinica, as described in
Kociolek et al. (2015), also shares many characteristics with Gomphonella olivacea and theGomphoneis taxa with four stigmata, except thatit has only one stigma.
Gomphonella or Gomphoneis?
The phylogenetic trees in this study show themonophyly of Gomphoneis okunoi and the genus
Gomphonella, though the emended description of
the genus Gomphonella by Jahn et al. (2019)
clearly excludes the taxa with stigmata. The typespecies of genus Gomphoneis is Gomphoneis elegans Cleve. This species has many (over four)
stigmata. However, no molecular information has

Gomphonella tetrastigmatum

67

Fig. 1. Phylogenetic position of Gomphoneis okunoi and related taxa determined by maximum likelihood (ML)method from rbcL. Taxonomic names are followed by GenBank accession numbers. Numbers at branches
indicate neighbor joining/ML bootstrap support values (only values higher than 70 are shown).

68

Akihiro TujiFig. 2. Phylogenetic position of Gomphoneis okunoi and related taxa determined by maximum likelihood (ML)method from 18S rRNA. Taxonomic names are followed by GenBank accession numbers. Numbers atbranches indicate neighbor joining/ML bootstrap support values (only values higher than 70 are shown).

been reported for this taxon. If G. elegans andthe genus Gomphonella are monophyly, andshould be regarded as the same genus, Gomphonella Rabenh. 1853 has priority over Gomphoneis Cleve 1894. Under the circumstances, it

is better to expand the deﬁnition of the genus
Gomphonella to include the Gomphoneis taxawith four stigmata. The similarity of the ultrastructure between the Gomphoneis tetrastigmatum species complex and Gomphonella olivacea

Gomphonella tetrastigmatum

69Fig. 3. Internal valve view. A–D. Headpoles. E–H. Footpoles. A, E. Gomphonella olivacea. B, F. Gomphoneis
okunoi. C, G. Gomphoneis pseudookunoi. D, H. Gomphoneis tetrastigmatum. Scales: 1 µm.

70

Akihiro TujiFig. 5. Internal valve view. A–B. Central area.
Gomphoneis tetrastigmatum. No stigma isobserved. Scales: 1 µm.

also supports the expansion of the deﬁnition ofthe genus Gomphonella. Gomphosinica may be asynonym of the genus Gomphonella, because
their morphological characteristics are identical
except for the presence of only one stigma. However, no molecular information has been published, and this issue requires further study.
Transfer of Gomphoneis taxa with four stigmata
to genus Gomphonella
Gomphonella quadripunctata (Østrup) Tuji,comb. et stat. nov.

Fig. 4. Internal valve view. A–D. Central area. A.
Gomphonella olivacea. B. Gomphoneis okunoi.
C. Gomphoneis pseudookunoi. D. Gomphoneis
tetrastigmatum. Only three stigmata areobserved. Scales: 1 µm.

Basionym: Gomphonema olivaceum var. quadripunctatum Østrup, Nov. Hedw. 48: 85. f. 11. 1908.
Synonym: Gomphonema quadripunctatum (Østrup)
Wislouch, Ber. dt. Bot. Ges. 42: 166. 1924.
Gomphoneis quadripunctatum (Østrup) P.A.Dawson
ex R.Ross et P.A.Sims, Bacill. 1: 162. 1978.

Gomphonella olivaceoides (Hust.) Tuji, comb. nov.

Gomphonella tetrastigmatum

Fig. 6. External valve view. A–D. Headpoles. E–H. Footpoles. A, E. Gomphonella olivacea. B, F. Gomphoneis
okunoi. C, G. Gomphoneis pseudookunoi. D, H. Gomphoneis tetrastigmatum. Scales: 1 µm.

71

72

Akihiro Tuji
Basionym: Gomphonema olivaceoides Hust., Arch.
Hydrobiol. 3: 397. pl. 37. f. 9–12. 1950.
Synonym: Gomphoneis olivaceoides (Hust.) J.R.Carterand Bailey-Watts, Nov. Hedw. 33: 566. pl. 9. f. 49–51.
1981. excl. ﬁgs et desc.
Gomphoneis olivaceoides (Hust.) J.R.Carter and Bailey-Watts ex. Tuji, Bull. Natl. Sci. Mus., Tokyo, Ser. B
31: 90–91. 2005.

Gomphonella calcifuga (Lange-Bert. et E.
Reichardt) Tuji, comb. nov.

Basionym: Gomphonema calcifugum Lange- Bert. & E.
Reichardt in Lange-Bert., Iconogr. Diatomol. 6: 53.
1999, nom. nov.
Synonym: Gomphonema olivaceum var. minutissimum
Hust. in Pascher, Süssw.-Fl., ed. 2, 10: 378. f. 720.
1930.

Gomphonella tetrastigmata (Horik. et Okuno)
Tuji, comb. nov.
Basionym: Gomphonema tetrastigmatum Horik. et Okuno
in Okuno, Bot. Mag. Tokyo. 58: 10. f. 3e. 1944.
Synonym: Gomphoneis tetrastigmata (Horik. et Okuno)
Ohtsuka, Diat. 18: 32. 2002.

Gomphonella okunoi (Tuji) Tuji, comb. nov.

Basionym: Gomphoneis okunoi Tuji, Bull. Natl. Sci.
Mus., Tokyo, Ser. B 31: 92–95. pl. 12. f. 1–10. pl. 13. f.
1–4. pl. 14. f. 1–5. 2005.

Gomphonella pseudookunoi (Tuji) Tuji, comb.
nov.

Basionym: Gomphoneis pseudookunoi Tuji, Bull. Natl.
Sci. Mus., Tokyo, Ser. B 31: 97. pl. 15. f. 1-15. pl. 16.
f. 1–5. pl. 17. f. 1–5. 2005.

Gomphonella hutchinsoniana (R.M.Patrick)Tuji, comb. nov.

Basionym: Gomphonema olivaceoides var. hutchinsoniana
R.M.Patrick, Limnol. Oceanogr. 16: 414. f. 1. 1971.

Gomphonella perolivaceoides (Levkov) Tuji,comb. nov.
Basionym: Gomphonema perolivaceoides Levkov,Iconogr. Diatomol. 16: 65–66. pl. 177. f. 1–21. 2007.

References

Fig. 7. External valve view of central area. A.
Gomphonella olivacea. B. Gomphoneis okunoi.
C. Gomphoneis pseudookunoi. D. Gomphoneis
tetrastigmatum. Scales: 1 µm.

Jahn, R., Kusber, W.-H., Skibbe, O., Zimmermann, J.,
Van, A., Buczkó, K. and Abarca, N. 2019. Gomphonella olivacea (Bacillariophyceae)—a new phylogenetic position for a well-known taxon, its typiﬁcation, new species and combinations. Plant Ecology andEvolution 152: 219–247.

Gomphonella tetrastigmatum
Kociolek, J.P., You, Q.-M., Wang, Q.-X. and Liu, Q.
2015. Consideration of some interesting freshwater
gomphonemoid diatoms from North America andChina, and the description of Gomphosinica, gen. nov.
Beihefte zur Nova Hedwigia 144: 175–198.
Tuji, A. 1995. Attached diatom assemblages in the ecotone of Lake Biwa. Diatom 11: 17–24. (In Japanese.)Tuji, A. 2000. The effect of irradiance on the growth ofdifferent forms of freshwater diatoms: Implications for
succession in attached diatom communities. Journal ofPhycology 36: 659–661.

73

Tuji, A. 2005. Taxonomy of the Gomphoneis tetrastigmata species complex. Bulletin of the National
Museum of Nature and Science, Series B 31: 89–108.
Tuji, A., Mohri, Y., Ki, J.-S., Jung, S.W. and Julius, M.L.
2014. Phylogeny of Praestephanos gen. nov. (Thalassiosirales, Bacillariophyceae) based on Stephanodiscus
suzukii, and related freshwater thalassiosiroid diatoms.
Plankton and Benthos Research 9: 132–140.
Watanabe, T., Ohtsuka, T., Tuji, A. and Houki, A. 2005.
Picture Book and Ecology of the Freshwater Diatoms.
666 pp. Uchida-rokakuho, Tokyo (in Japanese).