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 architecture of the peristome teeth. Among diplolepideous mosses, three peristome-types have been recognized. The development of the amphithecium in taxa characterized by an Orthotrichum-type peristome is described here, thereby completing 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 to all other arthrodontous mosses that have been studied. The subsequent anticlinal divisions occurring in the eight celled Inner Peristomial Layer are clearly asymmetric. Lack of alignment of adjacent anticlinal IPL and Primary Peristomial Layer walls is further accentuated by post-divisural lateral displacement of the IPL walls due to swelling of the PPL cells. This development of the amphithecial layers yielding a 4:2:4 pattern in the Orthotrichaceae is identical to that described for the Bryum-type peristome. The asymmetry of the critical late stage division in the IPL is considered homologous between these types. Based on recent phylogenetic hypotheses for the Bryopsida, we propose to extend this homology assumption to the Haplolepideae, the Diphysciales, and the Tetraphidales, suggesting that the asymmetric division is likely plesiomorphic within the Arthrodonteae. Whether the peristome of the Orthotrichaceae represents a primitive bryalean peristome, or whether it arose through reduction of a bryoid-type remains to be addressed further.

Duke Scholars

Author A. Jonathan Shaw Biology