Cosmarium pachydermum var. aethiopicum (West & G.S.West) West & G.S.West (1905: 140)

Ramos, Geraldo José Peixoto, Bicudo, Carlos Eduardo De Mattos & Moura, Carlos Wallace Do Nascimento, 2018, Some new, rare and interesting desmids from bromeliad phytotelmata in Brazil, Phytotaxa 346 (1), pp. 59-77 : 65

Cosmarium pachydermum var. aethiopicum (West & G.S.West) West & G.S.West (1905: 140) ( Figs 39–43 )

Cell dimensions: 110–120 μm length, 87–90 μm width, 30–37 μm isthmus.

Material examined: BRAZIL, Bahia, Santa Teresinha, Serra da Jiboia. 14-I-2015, G. J. P. Ramos et al. s/n ( HUEFS 224653), 18-VII-2015, G. J. P. Ramos et al. s/n ( HUEFS 224673), 20-XI-2015, G. J. P. Ramos et al. s/n ( HUEFS 224711).

Habitat: bromeliad tanks ( Alcantarea nahoumii ); T 26.8 (± 3.4 ºC). pH 6.2 (± 0.7). C 0.26 (± 0.14 mS. cm-1). TDS 0.13 (± 0.06 ppt). DO 6.0 (± 1.5 mg.L- 1).

Notes: The cells of Cosmarium pachydermum var. aethiopicum have smooth outlines and are broadly elliptic rather than broadly oval, with thinner cell walls than in the nominate variety ( Coesel & Meesters 2007). This taxon was previously identified from bromeliads at Serra da Jiboia as C. ralfsii (= Micrasterias ralfisii (Brebisson ex Ralfs) Skaloud et al. ) ( Ramos et al. 2011), however after reanalysis of the material we have identified it now as C. pachydermum var. aethiopicum . Confusion between those two taxa has been very common in floristic studies in Brazil, and although part of the literature considers the size of the isthmus as the main diagnostic feature, we consider the apical view to be a more relevant morphological feature for differentiating them. In apical view, C. pachydermum var. aethiopicum presents an ellipsoidal cell, whereas C. ralfsii (= M. ralfisii ) appears fusiform.

There are only three records of C. pachydermum var. aethiopicum in Brazil, two from São Paulo ( Taniguchi et al. 2003, Araujo 2006) and one from Mato Grosso do Sul ( Santos 2008). The present record is the first from northeastern Brazil.

Figures

FIGURES 26–48. Cosmarium majae: LM (26–33); SEM (33), ventral view (27, 29–31, 33), apical view (26), lateral view (28) and zygospore (32); C. oliveirae: LM (34–37); SEM (38), ventral view (34–35, 38), apical view (36), lateral view (37); C. pachydermum var. aethiopicum: LM (39–42); SEM (43), ventral view (39–40, 43), lateral view (41), apical view (42); C. pseudoconnatum: LM (44–47); SEM (48), ventral view (44–45, 48), apical view (46–47). Scale bar 10 μm (26–32, 34–38, 44–47), 5 μm (33), 20 μm (39–43).