Stauroneis alabamae Heiden

Tusset, Eduardo A., Tremarin, Priscila I. & Ludwig, Thelma A. V., 2018, Two new Stauroneis species (Bacillariophyta, Stauroneidaceae) from midwestern karstic Brazilian formations, Phytotaxa 358 (3), pp. 265-277 : 268-269

Stauroneis alabamae Heiden in Schmidt, pl. 242: fig. 2. 1903. ( Figs 1‒10)

Valves rhombical-lanceolate, 122‒163 μm long and 28‒35 μm wide (n=15), with slightly protracted, rostrate apices. Pseudosepta absent. Raphe sternum linear. Raphe lateral with weakly expanded proximal endings. External distal raphe endings hooked to secondary side, terminate internally in prominent helictoglossae. Stauros narrow, nearly rectangular. Striae uniseriate, parallel to radiate, becoming convergent towards apices, 13‒17 in 10 μm. Areolae transversely elongate and irregularly spaced, 10‒13 in 10 μm. Girdle composed of two open bands.

Occurrence in samples: UPCB 78252, 78253.

Stauroneis alabamae illustrated by Heiden in Schmidt (1903) and Hustedt (1927‒1966) are similar to this karstic population. The species ultrastructure is illustrated for the first time here. Stauroneis nobilis Schumann (1867: 59) resembles S. alabamae in valve outline, irregular spacing of areolae and the shape of stauros. However, the former species has narrow, long protracted ends, and an accentuated undulation at the apical margin ( Hustedt 1931 ‒1959, Patrick & Reimer 1966, Joh 2015). Stauroneis akamina Bahls (2010: 36) also shows a similar valve outline and irregularly spaced areolae, but differs from S. alabamae by the smaller size of valves (length 63‒140 μm and width 16‒24 μm), higher stria density (16‒24 in 10 μm) and by the broader stauros ( Bahls 2010), twice as wide.

Stauroneis alabamae has been recorded in Africa ( Smith et al. 2015), Europe ( Hustedt 1931 ‒1959, Németh 2005), North America ( Schmidt 1903, Kociolek 2005), Asia ( Joh 2015), and Brazil ( Metzeltin & Lange-Bertalot 2007, Torgan et al. 1999). Our population is similar to S. nobilis f. alabamae (Heiden) A. Cleve-Euler ( Cleve-Euler 1953: 212) illustrated by Hustedt (1931 ‒1959, figs 1125 c, d), with slightly protracted rostrate apices, and weakly undulated apical margins. A similar valve outline is described (p. 242) and illustrated (fig. 87: 1, 2) by Krammer & Lange-Bertalot (1986) and although denominated as S. nobilis , certainly both populations belong to the same species. Hustedt (1931 ‒1959) stated that S. nobilis f. alabamae shows protracted ends with convex apical margins, not “broken angled” as in S. nobilis .

Metzeltin & Lange-Bertalot (2007) present S. alabamae , and accept as synonyms S. nobilis fo. alabamae ; S. anceps var. birostris (Ehrenberg) Cleve (1894:147) . The illustrated specimens from Ilha do Macaco, State of Pará, Brazil (see, pl. 118 figs 2‒3), were characterized by long protracted ends and slightly undulated apical sides.

The drawing of S. alabamae type material shows a broadly lanceolate valve narrowing to protracted ends, and apical margins are not undulated ( Schmidt 1903).An analysis of S. alabamae type based on LM observations was never made, and the species taxonomic identification seems to have been following Hustedt’s concept. The valves illustrated by Joh (2015) are rhombic-lanceolate sharply narrowing towards the not protracted ends, somewhat different from the original drawing of S. alabamae and from Hustedt’s illustrations. Further studies may show that they represent different taxa.

The species occurred in the plankton and epiphyton of a lentic environment (lagoon in the Estância Mimosa farm) that has alkaline water (pH 8.3) and moderate conductivity (380 μS/cm). Except for Metzeltin & Lange-Bertalot (2007) register of S. alabamae to Ilha dos Macacos, the other Brazilian records ( Torgan et al. 1999) of the species were not possible to confirm, due a lack of illustrations.