Micrasterias fimbriata var. spinosa Biss.

Micrasterias fimbriata var. spinosa Biss. **

( Fig. 4D View FIG )

Annals of Scottish Natural History 1893 (7): 173 ( Roy 1893). — Micrasterias apiculata f. spinosa (Bisset) West & G. S. West , A monograph of the British Desmidiaceae. II: 100 ( West & West 1905).

DISTRIBUTION. — Cosmopolitan. Amazon Basin: no records. Western Amazon: no records.

DESCRIPTION

Cells 256.0-259.5 µm long, 194.1-196.1 µm wide; isthmus 33.1-36.4 µm; apex: 70.0-79.5 µm; cells 1.3 times longer than wide. Cell wall with small denticles, especially along the main incisions, but their arrangement is not always regular.

The polar lobe has two two-denticulated marginal apices, which are curved and longer and thinner than the denticles on the lateral lobes; there are two subapical spines on each apical lobule. The terminations of the lateral lobes are truncated, rounded, with the presence of two robust and short denticles, accompanied by at least two shorter and less robust ones. At the concave apical margin of the polar lobes, the cell wall presents a clearly visible fringe of granules.

REMARKS

Recent works byNeustupa et al. (2011, 2014) resolved the species delimitation between Micrasterias fimbriata Ralfs , M. rotata Ralfs , M. brachyptera Lundell , and M. apiculata Meneghini ex Ralfs using geometric morphometrics, and genetic analyses. Neustupa et al. (2011) found two phylogenetic lineages for M. fimbriata , one geographically centred in eastern Europe and the British Isles (B-lineage), and one found in North America and western Europe (A-lineage). Our specimens coincided with the B-lineage of M. fimbriata . Posteriorly, Neustupa et al. (2014) described M. compereana to accomodate specimens formerly included within traditional M. fimbriata but with different phylogenetic position and morphological features. According to those authors, M. fimbriata sensu stricto most likely is restricted to temperate and boreal regions of Europe and Asia. As mentioned in Neustupa et al. (2011, 2014) the shape of the terminal lobes is key to identify M. fimbriata , and our specimens clearly present truncated lobes with spines, while surface spine layers on cells can be found in M. fimbriata var. spinosa as well as in M. compereana , so, that last character is not exclusive for M. fimbriata var. spinosa . Our specimens of M. fimbriata var. spinosa are morphologically similar to the drawings of the original description in Roy (1893) but ours are larger in longitude and shorter in breadth, having an elliptic contour instead of being circular.