Xanthidium verrucosum M.A.Santos, G.J.P.Ramos & C.W.N.Moura, 2022

Santos, Maria Aparecida Dos, Ramos, Geraldo José Peixoto & Moura, Carlos Wallace Do Nascimento, 2022, Taxonomic notes on genera Bourrellyodesmus and Xanthidium (Zygnematophyceae) from Chapada Diamantina, Bahia, Brazil, Phytotaxa 536 (3), pp. 228-242 : 239-240

Xanthidium verrucosum M.A.Santos, G.J.P.Ramos & C.W.N.Moura sp. nov. ( Figs 7 , 55–65 )

Diagnosis:—Cell approximately as long as broad (excluding spines), deeply constricted, sinus narrow, linear. Semicells semicircular, lateral margins convex, decorated with six pairs of upward-facing spines (four arranged at the apical margin and two spines at lateral, near the apical margin of semicells), with mamillate base; sometimes one pair of tiny spines straight in each basal angle; three or four large warts in the semicells center; semicell subcircular in lateral view; elliptic in apical view, with a pair of spines in the angles, and 3–4 warts on each side. Cell wall hyaline, sometimes brownish, punctate, with 3–4 median facial warts. Chloroplast with two pyrenoids per semicell. No zygospores were observed. Cell dimensions: length without spines 55–58 μm, with spines 67–95 μm, width without spines 51–55 μm, with spines 63–95 μm, thickness 42–50 µm, isthmus 33–34 μm, spines 9–25 μm long.

Holotype:—Material numbered ( HUEFS 253753 !) [pro parte], deposited at Herbarium of State University of Feira de Santana, population partially illustrated here ( Figs 7 , 52–62 ).

Paratype:—Material numbered ( HUEFS 253766 ) [pro parte], deposited at Herbarium of State University of Feira de Santana .

Type locality:— BRAZIL. Bahia: Andaraí, Marimbus do Baiano, Lagoa do Baiano , Lat. 12°45’52.4”S, Long. 41°18’34.5”W, 09 April 2018, M. A . Santos , J. T . X. Neto & F. M . Costa s/n ( HUEFS 253753 ) .

Habitat:—The new species was rarely found in the study area, generally associated to periphyton of C. caroliniana and U. foliosa ; EC 0.02 mS. cm-1 (±0.01); DO 7.4 (±1.2); TDS 0.02 (±0.01); pH 8.2 (±0.5); T ° C 30 (±1.4); WT 71.8 (±3.9) cm.

Etymology:—The specific epithet refers to the surface ornamentation composed of warts arranged on the face of the semicells.

Differential diagnosis:—The present taxon differs from other species of the genus Xanthidium by having semicircular semicells with convex lateral margins, decorated with six pairs of upward-facing spines with a mamillate base, and ornated with 3–4 large warts on the face of the semicells in the frontal view.

The newly described species resembles Xanthidium paulense Borge (1918: 42) due to the shape and size of the cell, and the arrangement of the spines. However, the latter species differs in that it has superior angles of semicells decorated with single spines, and each semicell face is decorated with one convergent spine.

Xanthidium verrucosum is similar to Xanthidium cristatum Brébisson ex Ralfs (1848: 115) , but the latter differs by having 10 marginal spines per semicell (four pairs and two singles at the base on each side), one or two warts in the semicell center (sometimes strongly reduced or even lacking), and relatively small cell size (40 x 35 μm without spines) ( Šťastný et al. 2013).

In the study area, we observed some morphological variations in the specimens: warts can be 3–4 per semicell; the spines (12) per semicell may be shorter (9–16 μm) or longer (23–25 μm), and some individuals may have an additional pair of tiny spines (2–5 μm), one at each basal angle.

Despite the polymorphism observed, X. verrucosum presents a distinct morphological pattern, which is different from any other known species of the genus Xanthidium .

Figures

FIGURES 7. Line drawings. Xanthidium verrucosum sp.nov.

FIGURES 48–65. Xanthidium trilobum (48–54): frontal view (48, 53), lateral view (49), apical view (50), detail of central ornamentation circled on semicell of Fig. 48 (51), cell–division (52), zygospore (54). Xanthidium verrucosum sp. nov. (55–65): frontal view (55, 59, 62–65), lateral view (56, 61), apical view (57–58, 60), morphological variation of the ornamentation (55, 65) and spines size (63–65). Cell formation (65), showing a tiny spine on the basal lobe (arrows). Scale Bar: 40 μm, except Fig. 54 (50 μm, horizontal bar).