Micrasterias jenneri var. semicirculare G.J.P.Ramos & C.W.N.Moura, 2019

Ramos, Geraldo José Peixoto, Costa, Fabiana De Matos, Santos, Maria Aparecida Dos & Moura, Carlos Wallace Do Nascimento, 2019, Taxonomic novelties, new records, and rare species of desmids from the Chapada Diamantina region, Brazil, Phytotaxa 391 (3), pp. 185-196 : 192

Micrasterias jenneri var. semicirculare G.J.P.Ramos & C.W.N.Moura , var. nov. ( Figs 51–54 )

Diagnosis— This variety differs from the nominate variety by having a semicircular outline, with lateral lobes broadly rounded, whereas M. jenneri var. jenneri has an oblong outline and lateral lobes concave. Another difference from the nominate variety is the incision between the lateral lobes that is about the same size as the incision between the apical and basal lobes, being shorter in the nominate variety

Cell dimensions: length 145–165 μm, breadth 109–123 μm, apical lobe 32–64 μm, isthmus 32–36 μm.

Holotype: material numbered ( HUEFS 244148 !) deposited at Herbário da Universidade Estadual de Feira de Santana , population illustrated here in LM ( Figs 51–54 ).

Etymology: The epithet refers to semicircular outline of the cells.

Type locality and habitat characteristics: Collected at “Vale do Capão”, Palmeiras, Bahia state, Brazil. Lat. 12º 30’ 31” S, Long. 41º 29’ 10” W. Sample collected by G. J. P.Ramos s/n ( HUEFS 244148) on 26 February 2017. Micrasterias jenneri var. semicirculare occurred in periphyton, with quiet and warm waters, associated to filamentous algae.

Notes: Micrasterias jenneri Ralfs (1848: 76) has been rarely reported in floristic studies in South America, and the few existing records are from material collected in Brazil ( Bicudo & Ventrice 1968, Bicudo & Picelli-Vicentim 1988, Moresco et al. 2009, Bicudo et al. 2015), and generally identified as Micrasterias jenneri var. simplex West (1890: 287) .

Tomaszewicz (1977) and Sormus (1991) discussed the relationships between the nominate variety and var. simplex , and concluded that the latter variety is a developing morphological expression (i.e., an immature form) of the former, in which the lateral lobes have not undergone a division process. Currently, Micrasterias jenneri var. simplex is considered a taxonomic synonym of Micrasterias jenneri Ralfs ( Guiry & Guiry 2018) .

Regarding the new variety, Micrasterias jenneri var. semicirculare , a population analysis (ca. 50 specimens examined) indicated that the semicircular outline, broadly rounded in the lateral lobes, is consistent and distinct from the nominate variety (which has an oblong outline) described by Ralfs. The lateral lobes are also slightly different, being more concave in the nominate variety than in var. semicirculare . We therefore consider those features sufficient to propose this taxon as a new variety.

Micrasterias jenneri var. semicirculare can be confused with M. denticulata Brébisson ex Ralfs (1848: 70) , although the latter differs mainly by having lateral subdivided into lobules of the third or fourth order.

Figures

FIGURES 51–65. Micrasterias jenneri var. semicirculare (51–54): ventral view (51–53), lateral view (54); Micrasterias torreyi var. pseudocurvata (55–57): ventral view (55), lateral view (56), semicell (57); Staurastrum serriforme (58–62): ventral view (58–60), apical view (61,62); Tetmemorus furcatus (63–65): ventral view (63, 64), lateral view (65). Scale bar 30 μm (51–57), 10 μm (58–65).