Article

A comparative study of two subspecies of Sonchus asper growing in Bulgaria (subsp. asper and subsp. glaucescens) was performed. In both, the anthers are predominantly tetrasporangiate; meiosis in the microspore mother ceUs runs normaUy, and the simultaneously formed microspore tetrads are tetrahedral; the mature poUen is 3-ceUed; the embryo sac formation is of the Polygonum type; the embryo develops according to the Asterad type; and the endosperm is initially nucIear. S. asper proves to be a strongly proterandrous and sexuaUy reproducing species. Its two subspecies here studied can be distinguished, not only by their morphology but by embryological features as weU.