Lindavia rossii

Valves are disc-shaped, with a low mantle and a flat valve face. The marginal area is narrow and composed of evenly spaced, fine alveolate striae extending approximately ⅓ to ½ the valve radius into the central area. The striae form a uniform radial pattern around the margin of the valve face, but the length of individual striae vary slightly on close inspection. A submarginal internal foramen is visible on each stria. The central area is indistinctly colliculate with ornamentation of variable size, number, and arrangement. Ornamentation as seen in the LM is a combination of two or more (2-3(5)) central fultoportulae (Houk et al. 2010), and pits or depressions that do not fully penetrate the valve. Ornamentation may form linear, well-defined rows at 120° angles, loosely clustered rows, wedge-shaped groups, or have a nearly random distribution across the valve face. Sierra Nevada populations commonly show ornamentation loosely clustered into 3 wedges. A single rimoportula is present near the perimeter of the central area, but it may be difficult to distinguish in LM. Marginal fultoportulae are present on every second to fifth costa, but are not easily seen in LM.

TAXONOMIC NOTES: Cyclotella is one of the more difficult diatom genera to conclusively identify specimens to the species-level as there is much confusion within the literature concerning species boundaries. Many species may be polymorphic, heterovalvar, or show biogeographical variability which is not accounted for in current species descriptions. The ecology of most species is poorly known. Additionally, it has been suggested that the structure of the central valve face is so variable as to be irrelevant to the identification process (Knie and Hübener 2007). Some workers (e.g. Tuebner 1995, Cremer et al. 2001) choose to designate populations that show great, but intergrading, variability as "complexes", such as the Cyclotella rossii-comensis-tripartita complex of Cremer (2001) or the Cyclotella ocellata-krammeri-rossii complex of Knie and Hübener (2007). Until significant work is undertaken to conclusively determine the nature of C. rossii, the taxonomic and ecological relevance of it morphotypes, similar information on its associated species, using the term 'Cyclotella-complex' or differentiating morphotypes may be the most practical approach.

Other taxa that appear closely allied to Cyclotella rossii include C. krammeri, which was designated as a valid name for the (potentially) invalid Cyclotella kuetzingiana sensu Grunow 1878 non Thwaites 1848, but excludes C. kuetzingiana var. planetophora Cleve-Euler and C. kuetzingiana var. radiosa Fricke in Schmidt. Others (e.g. Houk et al. 2010) continue to recognize C. kuetzingiana Thwaites and state that it is synonymous with C. krammeri. The central area of C. kuetzingiana/krammeri is slightly undulate and much less colliculate than C. rossii. Areolae and/or depressions show no pattern, or a weakly radiate pattern (sensu C. kuetzingiana var. radiosa).

Cyclotella comta var. oligactis Grunow in Van Heurck is probably conspecific with C. rossii, but Häkansson (1990) could not conclusively determine the nature of C. comta var. oligactis from available material and thus designated C. rossii a new species.

Cyclotella tripartita was described from Alaska and is considered synonymous with C. comensis sensu Manguin non Grunow (Håkansson 1990). The valve face ornamention of C. tripartita forms a trefoil pattern, very similar to the pattern observed in some members of our population of C. rossii. The valve face of C. tripartita, however, is radially undulate, not flat. Houk et al. (2010) suggest that C. tripartita may be conspecific with C. rossii based on similar, but unspecified, ecologies.