Description: There are many claims in the literature of “morphological species” subdivided by “molecular cryptic species”. But both “morphological species” and “molecular species” are not concepts at all and are meaningless outside the context of a deeper analysis of “What is a species in the first place?” I will (over-)simplify the basic ideas of three popular approaches: the Biological Species Concept, the Phenetic Species Concept, and the Phylogenetic (Autapomorphic) Species Concept. All three make use of heritable traits of all kinds (behavioral, physiological, gene sequence, morphology, etc.) There is no reason to believe that one type is superior (for empirical analysis) to the other in all cases. In fact, I will show that in Stephanodiscus at least, morphological evolution has outpaced change in several so-called bar-code genes (i.e., analysis of morphology recovers multiple lineages within each of several different molecular species.) Other examples will include phylogenetic analysis of chloroplast and mitochondrial genomic data, barcode gene data, and qualitative and quantitative morphological data in the genera Cyclostephanos and Stephanodiscus (and apparent phylogenetic constraints on environmentally induced morphological variation in S. niagarae.)

Audience: Diatom taxonomists and systematists, those interested in using species level taxonomy for ecological monitoring studies, those interested in systematics and ecology of Stephanodiscus and Cyclostephanos, those curious about “cryptic species”.