Characteristics of achenes in Potentilla collina group [Rosaceae]

Achenes morphology in taxa from Potentilla collina s.l. i.e., P. collina Wibel s.s., P. leucopolitana P.J. Müller, P. thyrsiflora Hülsen ex Zimmet., P. thyrsiflora var. isosepala Th. W., P. silesiaca Uechtr. And P. wimanniana Günther and Schummel was examined with stereoscope and scanning electron microscopy. Achenes of these taxa varied slightly in shape, size and colour, while marked differences among them appeared in the surface sculpture and in the dimensions of aril, dorsal ridge and ribs. SEM analyses allowed to distinguish two distinct morphological types of achenes. Type I - with ruminate sculpture and aggregates of some material, various in shape and size, at the surface of partly destroyed epidermal cells covering fruit wall in P. leucopolitana, P. wimanniana and P. thyrsiflora. Type II - with ruminate-reticulate sculpture due to well preserved epidermal cells in P. silesiaca and P. thyrsiflora var. isosepala. The obtained results have supported Błocki’s suggestion to treat P. thyrsiflora var. isosepala as a separate species named P. isosepala. However, similarities in the surface sculpture of achenes in some taxa of P. collina group did not facilitate their classification, therefore this feature may be a valuable taxonomical criterium only in combination with others.