Morphological and cytological variation in Spergularia echinosperma and S. rubra, and notes on potential hybridization of these two species.

Morphological and cytological variation in Spergularia echinosperma and S. rubra and the possibility of these two species hybridizing were investigated. The plant material was collected mainly in the western- and southern-Bohemian pond basins where S. echinosperma is most abundant. Using flow cytometry, we found diploid and tetraploid cytotypes among plants morphologically identified as S. echinosperma and only tetraploid S. rubra. The two tetraploid cytotypes differed significantly in genome size. Both the diploid and tetraploid S. echinosperma and S. rubra also differed morphologically. The most important identification characters were stipule length together with stipule length/width ratio, seed colour, seed size and testa verrucosity. Although the morphological data suggest that tetraploid S. echinosperma may be a hybrid between diploid S. echinosperma and S. rubra, its genome size was significantly greater than that of a simulated allotetraploid. Since an increase in genome size following allopolyploidization is an improbable event, it is possible that other pathways were involved in the formation of tetraploid S. echinosperma. The nomenclature of S. echinosperma was also studied. Lectotypification of the name with a plant morphologically corresponding to the diploid cytotype is proposed. The morphological analysis also indicates that the holotype of S. ×kurkae, which was described as a putative hybrid between S. echinosperma × S. rubra, corresponds to tetraploid S. echinosperma.