The simple thalloid liverworts use several forms of asexual reproduction with gemmae often serving as significant taxonomic characters. Cavicularia densa Steph. (Blasiales, Marchantiophyta), a Japanese endemic, bears multicellular stalked gemmae within specialized receptacles. Two kinds of gemmae have been described: a lenticular, discoid form with serrulate margins and two opposite marginal notches, and a smaller, spherical form. Conversely, this small, spherical form has been considered a transitional stage to the serrulate form. Alternately, the presence of only one type of gemma has been used as an identifying character for the taxon. In this investigation, comparative light and scanning electron microscopy was performed on field collected materials to clarify the locations and morphological variations of C. densa gemmae. Sectioned thalli revealed the gemmae receptacles to be semi-enclosed, pillared chambers that contain numerous stalked gemmae at various stages of maturity. One gemma form is characteristically elliptical in surface view, fusiform in section with conoidal external cell surfaces. Another form, of similar structure, is more ovoid, lacks conoidal relief and is smaller at germination. Also present in the chamber are massive gemma-like structures whose potential for germination is questionable as no germinating structures were observed. Described for the first time are ventral gemmae, which occur in tightly arranged linear rows along the midline of the plant interspersed with the rhizoids. These gemmae are ellipsoidal with trapezoidal attenuation toward the apices and bases. The delineation of gemmae morphologies in C. densa, specifically the unique occurrence of ventral gemmae along with contained dorsal forms, provides a platform for the necessary ontogenetic studies required to ascertain phylogenetic relationships.

Key words: Cavicularia densa, gemmae