Gomphonema johnsonii Bahls, 2013

Bahls, Loren, 2013, New diatoms (Bacillariophyta) from western North America, Phytotaxa 82 (1), pp. 7-28 : 13-15

Gomphonema johnsonii Bahls , sp. nov. ( Figs 34–42 )

Valves lanceolate with narrow subrostrate apices. Valve length 24–50 µm; valve width 6.9–8.5 µm. Pore field present at the footpole. Valves somewhat asymmetric about the apical axis. Axial area narrow and linear, widening to merge with a moderately large elliptic central area. Raphe straight and weakly lateral, becoming filiform at the proximal and distal ends. Proximal raphe ends weakly expanded; terminal raphe fissures hooked to the side opposite the central stigma. Striae strongly radiate, 9–12 in 10 µm at the valve center, 14–18 in 10 µm near the apices. Areolae 30–35 in 10 µm. One stigma present at the end of the longest central stria.

Holotype: — USA, Oregon: Lane County, Spring along Forest Road No. 1900482, 44.1342 o N, 122.2286 o W, elev. 604 m, coll. A. Johnson, 10 August 2011. MDC sample 500301; holotype slide MDC 42-2 ( Figs 34–42 ) (circled holotype specimen in Fig. 38 ). MONTU!

Isotypes: —MDC slide 126-96 ( MONTU!); circled specimens on ANSP! GC 65164.

Etymology:—This taxon is named for Al Johnson, hydrologist with the Willamette National Forest and collector of the type sample.

Observations:—Under SEM, a well-developed apical pore field at the footpole and C-shaped external openings of the areolae are evident ( Fig. 42 ). Gomphonema parvulum (Kützing) Kützing (1849: 65) is smaller (10–36 µ m long) with less strongly radiate striae. Gomphonema gracile Ehrenberg (1838: 217) lacks protracted apices and also has more weakly radiate striae. Valves of Gomphonema mexicanum Grunow in Van Heurck (1880: pl. 24, fig. 3) are larger and lack the protracted headpole.

Distribution: — Gomphonema johnsonii is known to date only from the type locality.

Order Naviculales Bessey 1907: 10

Family Cavinulaceae D.G. Mann in Round et al. 1990: 659

Genus Cavinula D.G. Mann & A.J. Stickle in Round et al. 1990: 665

Figures

FIGURES 34–42: Gomphonema johnsonii from Spring on Road 1900482, Willamette National Forest, Oregon (type locality). Figs 34–40: LM images. Fig. 38: Holotype specimen. Fig. 40: Initial valve. Figs 41, 42: SEM images. Fig. 41: Whole valve, external. Fig. 42: Close up view of footpole showing apical pore field, distal raphe fissure, and C-shaped external areolae openings. Scale bars: Figs 34–41: 10 µm; Fig. 42: 3 µm.