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Abstract
Stauroneis phoenicenteron, the type species of Stauroneis, Stauroneis anceps (two moiphotypes) and S. legumen have Geitler's type IC auxosporulation, which has been demonstrated previously also in S. anceps var. siberica. Type IC auxosporulation is possessed by raphid diatoms with quite different valve, girdle and protoplast structure. This, coupled with the variation that occurs between type IC diatoms in, for example, the structure of the copulation envelope, auxospore shape, and the structure of the caps present at the ends of the auxospores, suggests that type IC auxosporulation is not in itself a reliable indicator of close systematic relationship. However, the particular kind of type IC auxosporulation found in Stauroneis also occurs in Craticula and “Navicula” protracta (but not in Navicula sensu strictó). All available evidence, from cell wall and protoplast characters, is consistent with the idea of a close relationship between these taxa and with the idea that the freshwater Stauroneis species belong together in the same genus. The evidence is not conclusive, however, since many of the shared features may be symplesiomorphies.
