Micrasterias radians W.B. Turner (1893: 91)

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 : 67-69

Micrasterias radians W.B. Turner (1893: 91) ( Figs 73–92 ).

Cell dimensions: 130–190 μm length, 103–150 μm width, 16–25 μm isthmus.

Material examined: BRAZIL, Bahia, Santa Teresinha, Serra da Jiboia. 14-I-2015, G. J. P. Ramos et al. s/n ( HUEFS 224657), 18-VII-2015, G. J. P. Ramos et al. s/n ( HUEFS 224676), 11-IX-2015, G. J. P. Ramos et al. s/n ( HUEFS 224704), 20-XI-2015, G. J. P. Ramos et al. s/n ( HUEFS 224718).

Habitat: bromeliad tanks ( Alcantarea nahoumii ); T 27.5 (± 2.8 ºC). pH 6.0 (± 0.5). C 0.24 (± 0.16 mS. cm-1). TDS 0.13 (± 0.10 ppt). DO 7.8 (± 4.2 mg.L- 1).

Notes: In a previous study ( Ramos et al. 2011), this taxon was identified as two distinct species: M. furcata C.Agardh ex Ralfs (1848: 73) and M. crux-melitensis Ralfs (1848: 73) . When we reevaluated the material examined by Ramos et al. (2011), together with new collections from the area, we were able to identify those taxa as Micrasterias radians . That desmid showed the highest degree of polymorphism in all taxa studied, often presenting anomalous forms. The phenotypic plasticity of that species generated forms very similar to taxa such as M. furcata C.Agardh ex Ralfs (1848: 73) (with elongated lateral lobes) and M. crux-melitensis Ralfs (1848: 73) (with short lateral lobes). Another variable feature was the base of the polar lobe, which ranged from straight to intumescent, and the shape of the apex: slightly curved or straight.

Authors such as Neustupa et al. (2010) and Coesel & Van Geest (2014) have discussed taxonomic problems in the Micrasterias radians complex, noting frequent confusion with the taxa mentioned above. Among the varieties of M. radians reported by those authors, the ones that are closest to the morphotypes from the Brazilian phytotelmata are M. radians var. radians and M. radians var. brasiliense (Grönblad) Willi Krieger & A.M.Scott. However , since their variation can be very wide, including with the presence of semicells with intermediary characteristics (in addition to other varieties of M. radians ), we considered it better to identify all of the variation as belonging to a single taxon: Micrasterias radians . We therefore recommend further studies, preferably using a polyphase approach, to evaluate whether the phenotypic diversity of the Micrasterias radians complex occurring in bromeliads from Serra da Jiboia corresponds to the phenotypic expression of a single species or to different taxa.

Figures

FIGURES 73–92. Micrasterias radians: LM (73–89); SEM (90–92), ventral view (73–76, 77–79, 82–92), apical view (80), lateral view (81) and anomalous forms (82–89). Scale bar 30 μm (73–89), 40 μm (90–92).