Contributor: Mark Edlund - May 2015
Length Range: 101-162 µm
Width Range: 22.5-26.7 µm
Striae in 10 µm: transverse striae 11.9-14.3; longitudinal striae 20.0-23.8
There are three valve types found for this taxon: vegetative, “heribaudii”, and craticula forms. The three forms are produced as a cellular strategy for surviving inimical conditions such as desiccation (Schmid 1979). Two craticula are formed within the vegetative frustule and subsequently the “heribaudii” cell is formed within the craticula. The heribaudii cell usually has different ornamentation compared to vegetative cell.
Vegetative valves are fusiform-lanceolate, with acutely rounded (shorter valves) to pointed apices (longer valves), never protracted. The axial area is narrow and strongly silicified. The central area is only slightly expanded. Raphe filiform to slightly lateral. Proximal raphe ends curve slightly to same side of valve and terminate in a small hook. Terminal raphe fissures are sickle-shaped and hooked toward the same side of the valve. Slit-like and apically elongate areolae arranged in both transapical and longitudinal striae, with transapical striae more prominent. Transapical striae are parallel throughout the valve, becoming slightly convergent near the apices. Longitudinal striae arranged in slightly wavy rows.
“Heribaudii” forms have similar shape, size, and raphe features as vegetative valves. Slit-like and apically elongate areolae (21 in 10 µm) are arranged only in transapical striae. Transapical striae radiate (1.9-11.6 in 10 µm) becoming parallel to convergent only at the valve ends.
The craticula forms have similar shape and size as the vegetative valves, but are very heavily silicified and comprise a central sternum, parallel transapical ribs (1.5-1.8/10 µm), a thick margin, and circular to oval to quadrilateral openings.
This taxon is later homonym of Navicula cuspidata var. obtusa Grunow 1860. These nomenclatural concerns need to be corrected.
Basionym: Navicula cuspidata var. obtusa
Author: Patrick 1966
Length Range: 127-146 µm
Width Range: 23-29 µm
Striae in 10 µm: 14-17 transverse, 24-28 longitudinal
Valve linear-lanceolate, gradually tapering to acute, rounded ends. Axial area narrow, distinct. Central area not clearly differentiated from the axial area. Striae parallel throughout the valve; punctate, the puncta forming longitudinal and transverse lines. Transverse lines, 15 in 10 µ. Longitudinal lines, 24-28 in 10 µ. Length, 127-146 µ. Breadth, 23-29 µ.
Boyer, C.S. (1927). Synopsis of North American Diatomaceae, Part II. – Naviculatae, Surirellatae. Proceedings of The Academy of Natural Sciences of Philadelphia 79: 229– 583.
Grunow, A. (1860). Uber neue oder ungenügend gekannte Algen. Verhandlungen der Kaiserlich-Königlichen Zoologisch-Botanischen Gesellschaft in Wein, 10: 503-582.
Héribaud, J. (1903). Les Diatomées Fossiles d’Auvergne (Second Mémoire). Librairie des Sciences Naturelles, Paris. pp. v-x, 1-166, pls 9-12.
Patrick, R.M. and Reimer, C.W. (1966). The Diatoms of the United States exclusive of Alaska and Hawaii, V. 1. Monographs of the Academy of Natural Sciences of Philadelphia 13.
Schmid, A.M. (1979). Influence of environmental factors on the development of the valve in diatoms. Protoplasma 99: 99-115. 10.1007/BF01274072
Navicula cuspidata var. obtusais known only from its type locality, Radford Peak, Colorado. Associated taxa include Hantzschia amphioxys.