ANATOMY AND DEVELOPMENT OF THE SPOROPHYTE OF GYROTHYRA UNDERWOODIANA HOWE

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  The western North American endemic Gyrothyra underwoodiana Howe has several unique characters which have been used to isolate it into a monotypic family. Among these are ventral stem cushions which give rise marginally to pigmented rhizoids, a dorsal vegetative appearance of Jungermannia coupled with large, bifid underleaves, unicellular apical gemmae, and spirally arranged, nonthickened capsule valves. Evaluation of the placement of the Gyrothyraceae Schust. in the Balantiopsidineae Schust. necessitates critical examination of developmental patterns, especially the seemingly nonvariable patterns of the sporophyte and associated gametophytic investments. These patterns have consequently been studied in natural and cultured populations, using the methods of serial microtome sectioning. The sporophyte is enclosed by a somewhat pendent, solid perigynium with the capsule apex embedded in stem tissue derived from the region of the archegonial cluster; a short, contracted, tubular perianth inserts at the perigynial apex. The large sporophyte foot is differentiated into an haustorial collar and conical basal zone. The seta in cross section is of Douin's (1908) general type. The capsule, which possesses a two-layered wall, is elongate and lacks secondary thickenings. The spiral arrangement of the capsule valves is significant in the dispersal of the small, punctate spores. Overall, these features indicate that the Gyrothyraceae is more closely related to the Geocalycineae Schust. than to the Balantiopsidineae.