Pinnularia subgibba var. lanceolata

Pinnularia subgibba var. lanceolata Gaiser & Johansen var. nov. (Figs 90, 91)

Valva linearilanceolata ad extrema rostrata decrescens, ratione longitudinis latitudine variabili, centro extremo 2-3plo latiore, 9-12 µm lata, 60-85 µm longa. Area axialis lata, circa 1/3 lata quam valva, ad extrema decrescens. Area centralis fascia transersa formans, interdum a striis paucis obliterata. Raphe filiformis fissuris terminalibus unciformibus. Striae ad centrum breves radiatae, ad extrema longae convergentes, 8-11 in 10 µm.

Valve linear-lanceolate, tapering to rostrate apices with variable length-to-breadth ratio, center of valve 2-3 times broader than the ends, 9-12 µm wide (mean = 10.8 µm), 60-85 µm long (mean = 74.7 µm). Axial area broad, about 1/3 breadth of valve, tapering at valve ends. Central area a transverse fascia, sometimes containing a few short striae. Raphe filamentous with rounded question-mark shaped terminal fissures. Striae short and radiate at valve center, longer and convergent towards valve ends, 8-11 in 10 µm.

Holotype: Dry Bay (Bay 31), 2-7-94, Epiphytic on Panicum stems (Gaiser Coll. No. EG940205, ANSP A-GC 57547a).

Isotype: Dry Bay (Bay 31), 2-7-94, Epiphytic on Panicum stems (Gaiser Coll. No. EG940205, ANSP A-GC 57547b).

Paratype: Dry Bay (Bay 31), 2-7-94, Epiphytic on Nuphar (Gaiser Coll. No. EG940209, CAS 219089).

Type locality: Epiphytic on stems of Panicum hemitomon in Dry Bay (Bay 31), a shallow Carolina bay on the Savannah River Site in Aiken County, South Carolina, U.S.A., 33°15' 0.36" N, 81°44' 46.1" W.

This taxon is related to the P. gibba Ehrenberg, P. subgibba and P. gibbiformis species complexes (including P. abaujensis). It conforms to any of these taxa with respect to valve length and breadth and density and character of the striae. However, the consistently rostrate ends set it apart from P. gibba, which has protracted, nearly capitate apices. It has a lower length to breadth ratio (approximately 6:1) than P. gibbiformis (10-12:1) and has a wider central area (6-8 µm) that usually contains a central fascia. We designate a new variety in the P. subgibba complex based on these characters.

Population characteristics: Taxon exhibits substantial variation in width of axial and central area. It often co-occurs with P. gibbiformis and P. subgibba var. gracilis.

Autecology and distribution: This taxon was found infrequently in 13 bays. It was uncommon to rare in Nelumbo lutea, Nuphar luteum, Panicum spp., Utricularia spp., leaf litter, sediment, woody debris, tree root, and phytoplankton samples. It was common in 3 bays in leaf litter, floating algal mat and Lemna spp. samples. Optimum pH (awm) = 5.2; water depth (awm) = 11 cm.

• Author
  Gaiser and Johansen 2000
• Length Range
  60-85 µm
• Width
  9-12 µm
• Striae in 10µm
  8-11