Xanthidium nordstedtii (Grönblad) Grönblad & A.M.Scott

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 : 237

Xanthidium nordstedtii (Grönblad) Grönblad & A.M.Scott in Scott et al. (1965: 48)

( Figs 4 , 31–39 , 66 )

Basionym: X. antilopaeum var. nordstedtii Grönblad (1945: 22 , fig. 152)

Synonyms:

X. antilopaeum f. Nordstedt (1878: 27, fig. 6)

X. antilopaeum var. ayayense Grönblad (1945: 21 , pl. 7, fig. 146)

Xanthidium mamillosum var. nordstedtii (Grönblad) Kurt Förster (1969: 62)

Cell dimensions:—length without spines 48–55 μm long, with spines 70–86 µm, width without spines 38–45 μm, with spines 60–90 μm, isthmus 11.5–14.5 μm, thickness 27–28 µm, spines 15–28 μm long.

Material examined:— BRAZIL. Bahia: Andaraí, Pantanal dos Marimbus, Lagoa do Baiano. Samples: HUEFS 253741, HUEFS 253742, HUEFS 253751, HUEFS 253752, HUEFS 253759, HUEFS 253766, HUEFS 253775, HUEFS 253777, HUEFS 253783, HUEFS 253804, HUEFS 253808 .

Habitat:—In the study area, this taxon was occasionally found associated to C. caroliniana and U. foliosa , and rarely to N. amazonum ; EC 0.02 mS. cm-1 (±0.01); DO 7.2 (±1.5); TDS 0.02 (±0.01); pH 7.0 (±0.9); T 30.4 ºC (±2); WT 65.9 cm (±17); N-NO 2 0.013 (0.005±); N–NO 3 0.024 (±0.016); N-NH 4 0.027 (±0.019); P–PO 4 0.019 (±0.013); O 4 Si-4 0.506 (±0.470).

Taxonomic notes:—This taxon was initially described by Grönblad (1945: 22, Pl. 7, fig. 152) for Santarém, Pará, Brazil, as Xanthidium antilopaeum var. nordstedtii and included X. antilopaeum forma ( Nordstedt 1878: 27, fig. 6) as a synonym of it. Grönblad characterized the taxon as having oblong semicells, open sinus, rounded ends, bearing 6 spines, single apical and double basal, transverse parallel to perpendicular, with an inflated base, and oblongrectangular in apical view.

Polyphasic study performed by Šťastný et al. (2013) with X. antilopaeum Kützing (1849: 177) from various European localities showed that the taxon forms a monophyletic lineage, composed by four monophyletic clades, characterized by wide cells with eight spines per semicell, differing from each other because of the arrangement of the spines, cell dimensions, and the pattern of the central ornamentation.

Morphologically, X. antilopaeum var. nordstedtii differs from the nominate variety by having six spines per semicell, a single in each apical angle and two in the basal ones, with longer spines and semicell more rotund in apical view ( Scott et al. 1965) and no central scrobiculae on face of semicells.

Grönblad & Scott in Scott et al. (1965: 48) raised the X. antilopaeum var. nordstedtii to species level, as X. nordstedii , and characterized it as having semicells broadly ovate, spines with swollen base, with two basal spines extending horizontally, and an apical spine directed outwardly and slightly upward; tumid apical view ( Scott et al. 1965, fig. 136–137). A couple of years later, Förster (1969: 62) reduced that species to variety of X. mamillosum Förster (1964: 411 as ‘mammillosum’), distinguishing it from the nominate variety by having no spine on the face of the semicells and having tumid cells in apical view.

According to Thomasson (1971: 43), X. mamillosum differs from X. nordstedtii by having spines rising from a swollen base, which is absent in the latter species. The author also commented on the morphological similarity of X. antilopaeum var. ayayense Grönblad (1945: 210 , Pl. 7, fig. 146) with X. nordstedtii , and except for the tumid apical view in the latter, there are no differences between both taxa, which we fully agree. In the present study, we observed some slight tumid semicells in the apical view and slight swelling at the base of the spines, although in others, it was difficult to distinguish, especially when the focus had not been properly applied. Furthermore, we observed variations in the size of the spines, since longer (22–28 μm) in some individuals to shorter (15–18 μm) in others.

Couté & Tell (1981: 196) carried out a SEM study from material collected in Argentina and Guyana, and identified the taxon under discussion as X. mamillosum var. borgei Kurt Förster (1981: 247) . Based on the images provided by the authors (Pl V, fig. 3–5), it is possible to observe semicells with punctuated walls, bearing six spines with slight swelling at the base. Thus, we consider it is more appropriate to accommodate that taxon as X. nordstedtii than as X. mamillosum var. borgei , the latter a misapplied name. This material was quite similar to the SEM image obtained from Bahia ( Fig. 66 ).

In addition to the type locality (Santarém, Pará), the taxon was registered in the states of Amazonas ( Thomasson 1971), Bahia (Oliveira et. al. 2011, as X. antilopaeum f.), Pará ( Grönblad 1945; Scott et al. 1965; Förster 1969, 1974, 1981, as X. mamillosum var. nordstedtii ), Minas Gerais ( Nordstedt 1878, as X. antilopaeum f.), and São Paulo ( Bicudo et al. 2018, as X. antilopaeum f.). It was the most common Xanthidium taxon in Marimbus do Baiano, occurring in 44% of the samples and registered in all macrophytes studied.

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).

FIGURES 66–67. Xanthidium nordstedtii (66): frontal view (SEM). Xanthidium trilobum (67): frontal view (SEM). Scale Bar: 20 μm.