Xanthidium regulare var. asteptum Nordstedt

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 : 238

Xanthidium regulare var. asteptum Nordstedt in Borge (1918: 43) ( Figs 5 , 40-47 )

Synonyms:

Xanthidium fragile Borge (1899: 17 ; Pl. 1, fig. 14)

Xanthidium fragile var. depauperatum Borge (1918: 41 ; Pl. 3, fig. 25)

Xanthidium regulare var. sexangulare Grönblad (1945: 22)

Xanthidium regulare var. sexangulare f. robustior Grönblad (1945: 22 , fig. 161)

Xanthidium sexangulare (Grönblad) Kurt Förster (1969: 62)

Xanthidium sexangulare var. robustius (Grönblad) Kurt Förster (1969: 63)

Cell dimensions:—length 70–81 μm (without spines), 117–120 (including spines), width 58–70 μm (without spines), 94–100 (including spines), thickness 48–56 µm, isthmus 22–27 μm, spines 15–23 μm long. Zygospore 90 µm in diameter (including spines), globular in shape and provided with short robust spines (10 μm).

Habitat:—This taxon was occasionally found in study area associated to C. caroliniana and U. foliosa ; EC 0.01 (±0.01) mS. cm-1; DO 6.5 (±0.8); TDS 0.02 (±0.02); pH 7.8 (±1); T 29.6 ºC (±2); WT 62 cm (±16).

Material examined:— BRAZIL. Bahia: Andaraí, Pantanal dos Marimbus, Lagoa do Baiano. Samples: HUEFS 253753, HUEFS 253754, HUEFS 253756, HUEFS 253757, HUEFS 253766, HUEFS 253768, HUEFS 253772, HUEFS 253775, HUEFS 253801.

Taxonomic notes:—Morphologically, Xanthidium regulare var. asteptum resembles X. regulare var. pseudoregulare (Borge) C.E.M.Bicudo & L.M.Carvalho (1969: 374, figs 10–12), although the latter differs by having semicells furnished by a single robust spine, which is 2–4 divided at the distal end, and having no tiny spine beneath each angle of the semicells.

We observed that zygospore of X. regulare var. asteptum without spines presents a cell more inflated (75–80 μm) than other of Xanthidium taxa analyzed in Marimbus do Baiano (ca. 50 μm), and distinct by ornamented by short, robust and pointed spines.

Couté & Tell (1981: 214, Pl. 10, fig. 4–5) presented details in the SEM of X. regulare var. asteptum , showing angles of semicells ornamented by solid spines bifid or trifid ones, curved, unequal, and a tiny spine in the basal angles of the semicells.

Although the type locality of this taxon is São Paulo (southeastern Brazil), the var. asteptum has been commonly reported in the northern Brazil (Amazonas, Amapá, Pará, Tocantins, Roraima), and sometimes in other regions such as northeastern (Maranhão, Pernambuco, Bahia), and Central-West (Mato Grosso).

Figures

FIGURES 1–6. Line drawings. 1. Bourrelyodesmus comperei sp. nov. 2. Xanthidium concinnum var. longispinum var. nov. 3. Xanthidium mamillosum var. mediolaeve. 4. Xanthidium nordstedtii. 5. Xanthidium regulare var. asteptum. 6. Xanthidium trilobum.

FIGURES 31–47. Xanthidium nordstedtii (31–39): frontal view (31, 32, 36–38), lateral view (34–35), apical view (33), morphological variation (36–38), spines base with slight swelling details (39). Xanthidium regulare var. asteptum (40–47): frontal view (40, 41), apical view (42–43), lateral view (44–45), detail of central ornamentation circled on semicell of Fig. 41 (46), zygospore (47). Scale Bar: 40 μm, except Fig. 47 (50 μm, horizontal bar).