The Evolution of Achene Morphology in Ceratophyllum (Ceratophyllaceae), III. Relationships of the "Facially-spined" Group

Abstract

Variational studies of Ceratophyllum demersum, C. oryzetorum, and C. platyacanthum indicate that these species are probably closely related but that each is separable by multivariate statistical analyses of morphological features. Basal, stylar, and facial fruit-spine lengths are cor- related in C. oryzetorum. In C. platyacanthum, however, correlations between spine lengths are less pronounced than in other species studied previously. The spiny, marginal achene wing of C. platyacanthum accounts for a major phenotypic difference between fruits of this species and those of C. demersum. Observations of phenotypically similar fruit mutations occurring sporadically in isolated populations of C. demersum indicate that the feature probably has a simple genetic basis. Regardless, the presence of facial spines and unusually long stylar and basal spines are characters which effectively separate both C. platyacanthum and C. oryzetorum from C. demersum. From inter- preting the results of variational analyses in context with phytogeographical and chromosomal data, a revised taxonomic scheme is proposed which maintains C. demersum and C. platyacanthum as distinct species, and recognizes C. oryzetorum as C. platyacanthum subsp. oryzetorum (V. Komarov) Les. In this third part of variational studies in Cer- atophyllum, relationships are investigated be- tween C. demersum L., C. oryzetorum V. Komarov, and C. platyacanthum Cham. The latter two species are the only members of the genus pos- sessing facial appendages on both fruit surfaces; hence the name facially-spined group is ap-