Achnanthidium petuniabuktianum, Pinseel & Vijver & Kopalova, 2015

Pinseel, Eveline, Vijver, Bart Van De & Kopalova, Kateřina, 2015, Achnanthidium petuniabuktianum sp. nov. (Achnanthidiaceae, Bacillariophyta), a new representative of the A. pyrenaicum group from Spitsbergen (Svalbard Archipelago, High Arctic), Phytotaxa 226 (1), pp. 63-74 : 68

Achnanthidium petuniabuktianum sp. nov. ( Figs 2–32 )

Frustules rectangular, only slightly arched in girdle view ( Figs 2 , 27 & 32 ). Cingulum composed of three open, unperforated copulae ( Figs 27, 32 ). Valvocopula typically showing two indentations at one third from the valve apex ( Fig. 32 ). Mantle areolae slit–like ( Figs 27 & 32 ). Valves linear with broadly rounded apices. Valve dimensions (n=20): length: 8.9–20.1 μm, width 1.9–2.9 μm. Raphe valve ( Figs 3–11 , Figs 20–26 ): valves concave. Axial area broad, linear, slightly narrowing towards the distal raphe endings ( Figs 20–22 ). Central area broad, forming a clear rectangular fascia ( Figs 20–22 ). Shortened marginal striae occasionally present in the central area ( Fig. 22 ). Central striae slightly more widely spaced ( Fig. 22 ). External raphe branches straight, filiform, slightly broadening towards the central area terminating in simple, straight to weakly bent proximal raphe endings ( Figs 20–22 ). External distal raphe endings terminating just beyond the last apical striae, distinctly unilaterally hooked ( Figs 20–23 ). Internal proximal raphe endings slightly bent in opposite directions, internal distal raphe endings straight terminating into small helictoglossae ( Figs 24–26 ). Distal raphe endings hardly discernible in LM. Striae, 39–44 in 10 μm, hardly visible in LM. In SEM, striae clearly parallel throughout the entire valve, composed of one to two transapically elongated areolae ( Fig. 20–23 ). Rapheless valve ( Figs 12–19 , Figs 27–31 ): valves convex. Axial area very broad, slightly narrowing towards the distal raphe endings ( Figs 27–28 & 30 ). Central area almost absent, formed by a slightly widening axial area ( Fig. 28 ). Central striae slightly more widely spaced ( Fig. 28 ). Central area occasionally lacking marginal striae thus forming a clear fascia ( Fig. 27 ). Striae, 38–42 in 10 μm, hardly discernible in LM. In SEM, striae parallel throughout, composed of usually one, rarely two, transapically elongated areolae ( Figs 27–28, 30 ).

Type:— NORWAY, SVALBARD ARCHIPELAGO. Spitsbergen: Petuniabukta, Mathiessondalen, epiphyton on moss from a wetland adjacent to a lake, sample SPITS 2013 /029, 30 m a.s.l., 78.56317° N and 16.58725° E, E. Pinseel, 26 July 2013 (holotype BR!, slide no. 4177, Botanic Garden Meise, Belgium; isotype PLP!, slide no. 288, University of Antwerp , Belgium) .

Etymology:— The specific epithet petuniabuktianum refers to the fjord area, Petuniabukta, where the new taxon was found.

Ecology, distribution and associated diatom flora: —So far, A. petuniabuktianum has only been found in Petuniabukta (Spitsbergen, Svalbard Archipelago). The new species is described from a wetland adjacent to a small lake characterized by an alkaline pH (8.1) and a moderately high conductivity value (761 μS/cm). At the type locality, this taxon was solely observed in association with moss vegetation, both submerged and terrestrial (wetland). A second population was observed in an epilithon sample of a shallow pond in the terminal moraine of a glacier. Due to logistic constraints, physicochemical measurements of this locality could not be obtained. In all cases, the abundances of this taxon were low (0.5–3.8% of all counted valves). The associated diatom flora was dominated by species of the A. minutissimum complex, Denticula tenuis Kützing (1844: 43) , D. kuetzingii Grunow (1862: 546) , Staurosirella aff. lapponica (Grunow in Van Heurck 1881: 45) D.M. Williams & Round (1987: 274), two at present unidentified Encyonopsis Krammer (1997: 91) taxa and Nitzschia cf. perminuta (Grunow in Van Heurck 1881: 68) Peragallo (1903: 672).

Figures

FIGURES 2–26. Achnanthidium petuniabuktianum sp. nov. Light and scanning electron micrographs. All pictures taken from the type population (BR-4177). 1. LM view of a frustule in girdle view. 3–11. LM views of raphe valves. 12–19. LM views of rapheless valves. 20–22. SEM external views of an entire raphe valve. 23. SEM detail of the distal raphe ending of a raphe valve. 24. SEM detail of the internal raphe valve. 25–26. SEM internal views of an entire raphe valve. Scale bars always 10 μm, except Figs 23–24 where scale bar is 1 μm and Fig. 25 where scale bar is 5 μm.

FIGURES 27–32. Achnanthidium petuniabuktianum sp. nov. Light and scanning electron micrographs. All pictures taken from the type population (BR-4177). 27–28. SEM external views of an entire rapheless valve. 29. SEM internal view of an entire rapheless valve. 30. SEM detail of an external rapheless valve. 31. SEM detail of an internal rapheless valve. 32. SEM view showing a frustule in girdle view. Scale bars always 10 μm, except Figs 30–31 where scale bar is 1 μm.