Crum, Howard Formerly, Herbarium, University of Michigan, Ann Arbor, Michigan.
A subclass of the mosses (class Bryopsida) consisting of two families and three genera, especially characterized by growth from protonematal flaps, three-ranked leaves, and peristomes of four teeth made up of whole cells (rather than thickened parts of cells). The Tetraphididae include small acrocarpous mosses with peristome teeth in fours (see illustration). The plants grow from buds produced on leaflike protonematal flaps. They are erect and simple or merely forked, with oblong-ovate leaves in three rows. The leaves usually have a single costa that ends near the apex. The cells are short and smooth. Brood bodies are generally present in terminal clusters with or without a cuplike whorl of differentiated leaves. The setae are elongate, and the capsules are cylindric to ovoid-cylindric and erect, with a distinct suboral rim of dark cells. The operculum is conic or subulate-pointed, and the peristome teeth are wedge-shaped, consisting of elongate cells thickened all around and derived from the entire tissue internal to the operculum. The calyptrae are mitrate and plicate. Chromosome numbers are 7 and 8. See also: Bryophyta; Bryopsida
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