Micrasterias radians var. brasiliensis (Grönblad) Willi Krieg. ex Coesel & van Geest

Micrasterias radians var. brasiliensis (Grönblad) Willi Krieg. ex Coesel & van Geest * ( Fig. 5C View FIG )

Plant Ecology and Evolution 147 (3): 400 ( Coesel & van Geest 2014). — Micrasterias radiata var. brasiliensis Grönblad , Acta Societatis Scienctiarum Fennicae, Nova Series B, 2 (6): 15 ( Grönblad 1945).

DISTRIBUTION. — Pantropical. Amazon Basin: Thomasson (1971). As M. radiata var. brasiliensis : Grönblad (1945); Förster (1969); Uherkovich & Schmidt (1974); Uherkovich (1976, 1981); Uherkovich & Rai (1979); Gutiérrez & Cadima (2004); Melo et al. (2009). As M. furcata : Cadima (2013). Western Amazonia (lowlands): no records.

DESCRIPTION

Cells 146.0-160.4 µm long, 131.0-151.1 µm wide, isthmus 18.2-20.1 µm, apex 54.7-56.6 µm; cells are 1.1 times longer than wide. Cells with deep median constriction, median sinus open with acute angles, cell wall finely punctate. Semicircular semicells, five-lobed, apical lobe about subrectangular, apical margin concave, tips forming two elongated, divergent processes, with two curved teeth; lateral and basal lobes about V-shaped, similar to each other, divided into two-tooth lobules. One remarkable characteristic of all second order lobules, is that they are widened at their base, slightly tapering towards their apices, where they are divided into two curved teeth.

REMARKS

This taxon has been subjected to a long taxonomic confusion wandering continuously between M. radiata Hassall ex West & G.S.West , M. radians W.B.Turner , M. furcata C.Agardh ex Ralfs , and their varieties. Coesel & van Geest (2014) finally provided a valid positioning of the taxon into M. radians var. brasiliensis , providing an insightful discussion on the gradual differences among varieties of the Micrasterias radians complex. In our specimens, the apical lobes protrude slightly, while in Coesel & van Geest (2014) those lobes are markedly outstanding; also, teeth on apical lobules are longer than those observed in our specimens, although all other morphological characteristics and size range shown by these authors were very similar to our specimens. From the specimens in our samples, we can add that all second order lobules show a continuous tapering from their base towards the point where they diverge into teeth, which is also observed in Coesel & van Geest (2014) for the same taxon, in Blanco & Sánchez (1986) for M. radiata var. brasiliensis , and in Bourrelly & Couté (1982) for M. radiata var. radiata .