Ultrastructure of the placental region in Grimmia orbicularis Bruch (Grimmiaceae, Bryopsida)

The sporophyte-gametophyte junction in G. orbicularis is examined by means of LM and TEM, focusing especially on the characteristics considered to be of evolutionary and biological significance in mosses. The placenta of this species, although in general terms corresponding to a bryalean model, also exhibits some differences, in particular the presence of labyrinthine wall in-growths in non-epidermal foot cells, and a variability in the nature of tissue connecting the foot and the gametophyte strand of hydroids.