Pinnularia australomicrostauron, Zidarova & Kopalová & Vijver, 2012

Zidarova, Ralitsa, Kopalová, Kateŕina & Vijver, Bart Van De, 2012, The genus Pinnularia (Bacillariophyta) excluding the section Distantes on Livingston Island (South Shetland Islands) with the description of twelve new taxa, Phytotaxa 44, pp. 11-37 : 22-23

Pinnularia australomicrostauron sp. nov. ( Figs 135–159 )

Valvae lineares in speciminibus maioribus ad lineares-ellipticae in speciminibus minoribus marginibus parallellae ad moderate convexis. Specimina marginibus leviter undulates. Apices late subrostrati-subcapitati, leviter protracti ad late rotundati in specimibus minoribus. Longitudo 30–93 µm, latitudo 8.4–14.6 µm. Area axialis distincte lanceolata, angusta in apicibus, dilatans in aream centralem. Area centralis formans fasciam rhombicam, plerumque asymmetricam in speciminibus majoribus, latam. Striae centrales nonnullae abbreviatae in area centrali speciminum maiorum. Raphe lateralis terminationibus raphis proximalibus deflexis cum poris magnis guttiformibus. Fissurae raphis distales falcatae. Striae leviter ad moderate radiatae in media parte valvae, parallelae ad moderate convergentes ad apices, 12–15, pro parte maxima 13–14 in 10 µm. Lineae speciosae longitudinales nullae.

Valves linear in larger specimens to linear-elliptic in smaller specimens with parallel to moderately convex margins. Larger valves with weakly undulated margins. Valve apices broadly subrostrate-subcapitate, weakly protracted to broadly rounded in smaller ones. Valve dimensions (n=45): length 30–93 µm, width 8.4–14.6 µm. Axial area distinctly lanceolate, narrow near the apices and widening towards the central area. Central area forming a large rhombic, usually asymmetrical, fascia in larger specimens. Smaller specimens only with rhombic to rounded central area with shortened striae bordering the area. Raphe lateral with deflected proximal raphe endings terminating in droplike large pores. Distal raphe fissures sickle-shaped. Striae weakly to moderately radiate in the middle, almost parallel to moderately convergent towards the apices, 12–15, mostly 13–14, in 10 µm. Longitudinal lines absent.

Type:— Byers Peninsula, Livingston Island , South Shetland Islands , sample BY061, leg. B. Van de Vijver, coll. date 17/01/2009, slide no. BR-4256 (holotype BR), slide PLP-201 (isotype University of Antwerp, Belgium), slide ZU8/19 (isotype BRM) .

Habitat:— Pinnularia australomicrostauron is one of the most common species of Pinnularia on Livingston Island, often forming very large populations in a wide variety of habitats, both aquatic (pools and larger lakes) and terrestrial (e.g. wet soil and mosses around small water bodies).

Etymology:— The specific epithet refers to the geographic distribution of the species (Latin: ‘ australis ’ meaning southern) and the similarity to Pinnularia microstauron .

Observations:— Pinnularia australomicrostauron mostly resembles P. ventricodecrescens Kulikovskiy, Lange-Bert. & Metzeltin (2010: 365) , P. microstauron and P. rhombarea Krammer (in Metzeltin & Lange- Bertalot 1998: 185); it has been reported from Antarctica as P. microstauron . Pinnularia microstauron was originally described by Ehrenberg from plant roots in Brazil and until recently it was believed to be a polymorph species. Krammer (2000) suggested, however, that its plasticity might not be so large. According to his assumption, P. microstauron var. microstauron lacks undulated margins and has broadly rostrate to wedge-shaped ends. Parts of the Pinnularia australomicrostauron populations clearly show valves with undulated margins and ends that are broadly subrostrate to subcapitate. The new species has a higher stria density than normally observed in P. microstauron (9–11, rarely 15 in 10 µm vs. 13–14 in 10 µm in P. australomicrostauron ). The most distinctive feature separating the two species is the distance between the central raphe endings,which is much larger in the P. australomicrostauron when compared to Pinnularia microstauron s.s. Pinnularia microstauron var. nonfasciata Krammer (2000: 74) usually lacks a fascia, in contrast to P. australomicrostauron , where only in smaller individuals is a fascia absent. Other varieties of P. microstauron listed in Krammer (2000) are small enough not to be confused with P. australomicrostauron . Pinnularia rhombarea has a rather similar valve outline but is generally wider (width 10.5–16.o µm vs. 8.4– 14.6 µm) with a lower stria density (9–11 in 10 µm vs. 13–14 in 10 µm). Probably the most similar species is P. ventricodecrescens , originally described from South Georgia as P. krasskei var. ventricosa . Analysis of the type material indicated that in the latter, also the larger specimens lack a fascia, the valves have a higher valve width (13–16 µ m vs. 8.4–14.6 µ m) and clearly subcapitate apices. The longest specimens of P. australomicrostauron closely resemble P. krasskei , also described from South Georgia ( Krammer 2000). However, based on the analysis of type material, the latter always has strictly parallel margins with broadly rounded, never protracted apices, a larger valve width (15–16 µm vs. 14.6 in the largest specimens of P. australomicrostauron ) and a lower stria density (9–11 in 10 µm vs. 12–15 in 10 µm).

Figures

FIGURES 135–152. Pinnularia australomicrostauron sp. nov. from Livingston Island. Figs 135–152. LM of P. australomicrostauron, smaller forms. Scale bar = 10 µm.

FIGURES 153–159. Pinnularia australomicrostauron sp. nov. from Livingston Island. Figs 153–159. LM of P. australomicrostauron, larger forms. Scale bar = 10 µm.