Euastrum evolutum var. truncatum F.M. Costa & C.W.N.Moura var. nov. (Figs. 5, 24–28)

Diagnosis: —Cells rectangular, median constriction deep, sinus closed, linear; semicells subtrapeziform, central protrusion composed of four granules, one pair of scrobicules above; apical lobes truncate, median incision V-shaped, deep, and slightly open, angles decorated with one stout spine straight, lateral margins decorated with one median spine forming a subapical lobe, one scrobicule on the lateral side of the base of the lobe; angles basal lobes decorated with tiny spines; small scrobicules close to the isthmus; cell in apical view ellipsoid. Cell dimensions: length 37.4–40 μm, breadth 25.4–26.9 μm, apical lobe 15.7–16.2 μm, and breadth of isthmus 6.6–7.1 μm.

Holotype:— Material numbered (HUEFS 263037!) [pro parte], deposited at the Herbarium of State University of Feira de Santana, population partially illustrated here (Figs. 5, 24–28).

Paratypes:— Material numbered (HUEFS 263038) [pro parte], deposited at the Herbarium of State University of Feira de Santana .

Type locality:— BRAZIL. Bahia: Camaçari, River Capivara Grande, Lat. 12°45’30.3’’ S, Long. 38°10’03.4’’ W, 29 November 2019, F. M. Costa & J. T.X. Neto s/n (HUEFS 263037).

Habitat:— Periphytic on Eleocharis acutangula; water conductivity 0.14 mS.cm-1 (± 0.08); dissolved oxygen 8.4 mg.L-1 (± 1.9); pH 6.3 (± 0.7); total dissolved solids 0.07 ppt (± 0.04); water temperature 30 ºC (± 0.3).

Etymology:— The specific epithet refers to the truncated apices of semicells.

Differential diagnosis:— Euastrum evolutum var. truncatum differs from the other varieties of E. evolutum by having apical lobes truncated, angles of the basal lobes decorated with few small spines and a central protrusion composed of four granules.

The morphologically closest taxon, E. evolutum var. integrius West & G.S. West (1896: 244), has basal lobes more prominent and rounded, robust subapical spine and a central protrusion composed of three granules. Also resembles E. praemorsum var. foersteri F.M. Costa, C.E.M.Bicudo C.W.N.Moura (2018: 199), although the latter differs by having concave apical lobes and basal lobes are less prominent.

We observed some specimens of Euastrum evolutum var. truncatum having slightly closed apical incisions, whereas others having spines of the apical angles slightly concave.

The use of SEM allowed the observing some tiny characteristics, such as the presence of scrobicules close to the isthmus and at the lateral side of the base of the apical lobe, not discernible in the LM.