Spore morphology in Pottia starckeana (Hedw.) C. Mull. (Pottiaceae, Musci) and its closest species

Resumen

Light, scanning, and transmission electron microscopy surveys of spore morphology and ultrastructure are given in order to provide some insight into the problematic taxonomy of the Pottia starckeana aggregate, including P. starckeana (Hedw.) C. Mull., P. davalliana (Sm.) C. Jens., P. commutata Limpr., and P. mutica Vent.Shared characteristics are noted, particularly in the fundamental wall structure, and two major spore types are described on the basis of their distinct shape, size, and sculptural pattern. Spores of type A, mainly with wavy outline and lacking marked perinous projections, correlate well with P. starckeana. Spores of type B, with regular outline, increased size, and more ornamented perine, characterize both P. commutata and P. davalliana. Much intergrading of spore morphology is noticeable, suggesting that localized introgressive hybridization may have taken place within the Mediterranean area involving these three species. No distinctive spore feature is considered useful for the taxonomic recognition of P. mutica. Furthermore, correlation is hardly ever found between spore type A and peristome structure. Resemblances between some spores of type A and certain spores from Encalypta (Encalyptaceae, Musci) seem to provide additional evidence for phylogenetic relationships between Pottiaceae and Encalyptaceae. Possibly adaptive characters of the sporoderm are discussed in relation to ecological and evolutionary considerations.