Peristome development in mosses in relation to systematics and evolution. V. Diplolepideae : orthotrichaceae

The classification of the Bryopsida is based-to a large extent on the archi tecture of the peristome teeth. Among diplolepideous mosses, three peristom e-types have been recognized. The development of the amphithecium in taxa c haracterized by an Orthotrichum-type peristome is described here, thereby c ompleting our survey of the ontogeny of all three diplolepideous peristome types. Patterns of early divisions leading to a three-layered amphithecium in Schlotheimia rugifolia, Ulota crispa, and U. hutchinsiae are identical-t o all other arthrodontous mosses that have been studied. The subsequent ant iclinal divisions occurring in the eight celled Inner Peristomial Layer are clearly asymmetric. Lack of alignment of adjacent anticlinical IPL and Pri mary Peristomial Layer walls is further accentuated by post-divisural later al displacement of the IPL walls due to swelling of the PPL cells. This dev elopment of the amphithecial layers yielding a 4:2:4 pattern in the Orthotr ichaceae is identical to that described for the Bryum-type peristome. The a symmetry of the critical late stage division in the IPL is considered homol ogous between these types. Based on recent phylogenetic hypotheses for the Bryopsida,: we propose to extend this homology assumption to the Haplolepid eae, the Diphysciales, and the Tetraphidales, suggesting that the asymmetri c division is likely plesiomorphic within :The Arthrodonteae. Whether the p eristome of the Orthotrichaceae represents a primitive bryalean peristome, or whether it arose through-reduction of a bryoid-type remains to be addres sed further.