This taxon is a member of the Cocconeis placentula species complex (also termed sensu lato). Note that for practical purposes, diatoms.org presents several varieties and species within the species complex. We recommend such treatment for assessment programs.
For those who wish to distinguish species in the strict sense (termed sensu stricto), the details are here.
The rapheless valves of C. placentula and C. placentula var. euglypta have a maximum of six longitudinal lines per hemivalve.
The valves of Cocconeis lineata and C. coreana are more elongate, elliptic, proportionally longer, and have more rounded apices.
The largest valves of C. czarneckii have a similar pattern in areolae to C. klamathensis and C. grovei. Cocconeis klamathensis, however, has large, strongly arched valves and C. grovei has larger valves, with lower stria density.
BioData Reference
Krammer and Lange-Bertalot 2/4 Pl 53 Fig 1-19