Pinnularia borealis var. pseudolanceolata Van de Vijver & Zidarova, 2011

Vijver, Bart Van De & Zidarova, Ralitsa, 2011, Five new taxa in the genus Pinnularia sectio Distantes (Bacillariophyta) from Livingston Island (South Shetland Islands), Phytotaxa 24, pp. 39-50 : 44-45

Pinnularia borealis var. pseudolanceolata Van de Vijver & Zidarova , var. nov. ( Figs 26–38 )

Valvae claro lanceolatae marginibus convexibus, apicibusque acute rotundatis, non protractis. Dimensiones (n=20): longitudo 21.5–47.3 µm, latitudo 7.5–9.5 µm. Area axialis angusta, linearis, dilatans ad aream centralem. Area centralis potius parva, rotundata, leviter asymmetrica. Fascia abest. Raphe fere recta ad leviter curvata terminationibus proximalibus guttiformibus leviter ad moderate deflexis. Fissurae distales unciformes. Striae transapicales densiores quam speciebus aliis sectionis Distantes , leviter ad fortiter radiatae in media parte valvae, parallelae ad leviter convergentes in apices, 6–8 in 10 µm.

Valves clearly lanceolate with convex valve margins and acutely rounded, non protracted ends. Valve dimensions (n=20): length 21.5–47.3 µm, width 7.5–9.5 µm. Axial area narrow, linear, widening towards the central area. Central area rather small, rounded, slightly asymmetrical, usually bordered by 1–2 (occasionally 3), short striae. Raphe almost straight to slightly curved with weakly to moderately (continuously) deflected to one side proximal, pore-like endings. Distal fissures weakly sickle-shaped. Transapical striae denser than other members of Distantes , weakly to strongly radiate in middle, occasionally almost parallel, becoming parallel to weakly convergent near apices, 6–8 in 10 µm, composed of 5–7 rows of very small, rounded pores ( Fig. 38 ).

Type:— Byers Peninsula, Livingston Island , South Shetland Islands , sample BY67, leg. B. Van de Vijver, coll. date 18/01/2009, slide no. BR-4234 (holotype BR), slide PLP-184 (isotype University of Antwerp, Belgium), BRM –7/97 (isotype BRM).

Habitat and Distribution:— Pinnularia borealis var. pseudolanceolata is rare on Livingston Island. A large population was observed in a large, circumneutral (pH 7.3) shallow pool on Byers Peninsula with low specific conductance values (<100 µS/cm) surrounded by fellfields and moss vegetations, growing into the water. Smaller populations were observed on Hurd Peninsula, situated in the southern part of Livingston Island (recorded by Zidarova 2008 as Pinnularia sp. A ) in a wide variety of samples, mainly on soil and mosses (both dry and semi-wet), rarely in pools, and always in low numbers. One population of Pinnularia borealis var. pseudolanceolata was observed on James Ross Island (Van de Vijver & Kopalová, unpubl. results).

Etymology:—The varietal epithet refers to the resemblance to P. borealis var. lanceolata Hustedt (in Schmidt et al. 1934: pl. 388, fig. 16–17).

Observations:—There are hardly any lanceolate taxa belonging to the Distantes group. Boye-Petersen described a P. borealis f. lanceolata Boye-Petersen (1928: 402) from Iceland but it is wider than P. borealis var. pseudolanceolata with a more broadly lanceolate valve outline (Table 1). Hustedt described P. borealis var. lanceolata from the Schwarzsee in Davos but the description was based on only two specimens (in Schmidt et al. 1934: pl. 388, fig. 16–17). Krammer (2000, 25) stated that “only single specimens have been found” and that more information is necessary to understand the correct identity of the species. Compared to valves of P. borealis var. lanceolata , as illustrated in Simonsen (1987: pl. 249, figs 4–7, illustrations of Husetdt’s type specimens), the Livingston populations have a higher number of striae (6–8 vs. 5 in 10 µm) and a lower valve width (10–12 µm for Hustedt’s specimens vs. 7.5–9.5 µm for specimens from Livingston Island) (Table 1). Pinnularia borealis var. undata Manguin (in Bourrelly & Manguin 1952: 80), described from Guadeloupe, is also wider (13.5 µm) with a lower number of striae (5 in 10 µm). In Frenguelli’s (1942) study, he illustrates several lanceolate valves of P. borealis but identifies them all as P. borealis s.l. Other lanceolate Distantes taxa are at present not known.

Figures

FIGURES 18–38. Pinnularia australoborealis sp. nov. and Pinnularia borealis var. pseudolanceolata var. nov. from Byers Peninsula. Figs 18–25. Pinnularia australoborealis sp. nov. Figs 18–24. LM of valves from the specimens of type population. Fig. 25. SEM of external detail of the central area with the central raphe endings. Figs 26–38. Pinnularia borealis var. pseudolanceolata var. nov. Figs 26–37. LM of valves from the specimens of type population. Fig. 38. SEM of external view of entire valve. Scale bar = 10 µm, except Figs 25 & 38, scale bar = 5 µm.