Seed and pollen morphology in the Orobanche alsatica complex (Orobanchaceae) from central Europe and its taxonomic significance

Abstract

Micromorphology of seeds and pollen of Orobanche alsatica, O. bartlingii and O. mayeri, the central European representatives of the O. alsatica aggregate (Orobanchaceae) was investigated on the basis of 32 samples from 18 localities in Poland, Slovakia, Czech Republic, Austria, Bosnia and Herzegovina, and Russia. Concerning seeds, the best taxonomic character is a narrow trough on external sides of radial walls of cells of the seed wall, which is always present and continuous in O. bartlingii, mostly absent in O. mayeri, and mostly present solely at wall segment junctions (vertices) in O. alsatica (individuals parasitising Peucedanum spp.; continuous in parasites of Seseli osseum). As for pollen, the exine sculpture is verrucate in O. mayeri, granulate in O. bartlingii, and granulate to scabrate in O. alsatica. O. alsatica parasitising Peucedanum spp. and Seseli osseum (host-related morphotypes) differ in seed shape, ornamentation and wall-perforation diameter. Variability of seed and pollen characters is high, and identical morphologies occur among the investigated species. The variation coefficient is too strongly correlated with the sample size to be a reliable estimator the taxonomic value of a character. Differences in seed and pollen sculpture, hosts and ecological preferences confirm the separation of the three examined taxa at species level.