Auxosporulation by a naviculoid diatom and the taxonomic implications

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Abstract
Auxospore formation by a littoral marine diatom, identified as Navicula ulvacea, was followed by the production of vegetative cells which on the basis of valve morphology would be placed in a different species, N. subinflatoides. As circumstantial evidence indicated that paedogamy was occurring, which would exclude the possibility of hybridization, auxosporulation shows that the specific limits have been too narrowly drawn, and both large and small forms should be included in the same species, N. ulvacea. Sizable populations of diatoms must be observed before new species are described. The validity of particular valvar features for species delimitation is discussed. Auxospores of another morphologically similar species, N. subinflata, were also observed, but this is probably separate from N. ulvacea. The position of N. aberrans in relation to the above species is briefly considered.