SPORE MORPHOLOGY IN THE MOSS GENUS PTERYGONEURUM JUR (POTTIACEAE)

This study presents a critical and detailed investigation of spore mor phology in the moss genus Pterygoneurum (Pottiaceae) using LM, SEM, an d TEM. Spores of this genus have not been studied previously. This pap er treats all species worldwide. There are several distinguishable spo re types within the genus. A group consisting of P. ovatum, P. medium, P. compactum, and P. sampaianum is characterized by spores with simpl e, branched or tooth-like processes. The ranges of variability in the shape and distribution of the surface processes and in spore morpholog y overlap for all species. This group could reflect interspecific and interpopulational gene flow. P. subsessile is distinctive in its large spores and multi-stalked processes, often separated by psilate areas. It could represent a transition towards cleistocarpous genera of the Pottiaceae such as Acaulon and Phascum. P. californicum is characteriz ed by spores with granula-like processes separated by broad psilate ar eas; it shows some morphological convergence with the former species. Spores of P. macleanum and P. kemsleyi show a basal layer of granula a nd, overlying this, irregularly arranged larger processes. Spores of P . lamellatum and P. arcticum are densely covered with granular process es sometimes connected in short ridges. This spore type is reminiscent of that of Crossidium, which, together with other shared features, le nds support to the view that Pterygoneurum could have evolved from anc estors of Crossidium.