Anatomy and ultrastructure of the sporophyte of Takakia ceratophylla (Bryophyta).

In this study, morphogenesis and structure of the sporophyte of Takakia ceratophylla are characterized beginning with the late embryo and culminating in the fully dehisced capsule. Information is presented on the development, ultrastructure, and anatomy of the three organographic regions of the sporophyte, namely capsule, seta, and foot. Diagnostic features that identify Takakia as a moss include the gradual elongation of seta, persistence of an apical calyptra, expansion of the capsule after cessation of seta elongation, existence of a columella, monoplastidic meiosis, spore ultrastructure (including a perine layer deposited late in spore wall (development), and the structure of the foot. Commonalities with the capsule of the Andreaeopsida include sporogenous tissue that overarchs a central columella, absence of stomata, and lack of a peristome and operculum. Peculiarities of the genus are seen in the internal structure of the capsule, the disintegration of the columella with spore maturation, and the dehiscence of the capsule along a single, spiralled, longitudinal suture line. Passive spore dispersal through longitudinal splitting of the capsule occurs in andreaeopsid mosses, liverworts, hornworts, and seedless vascular plants. The precise mechanism of dehiscence along a spiralled suture is unparalleled in extant archegoniates but finds counterparts in ancestral land plants such as the pteridophyte Tortilicaulis.