JONES, NICOLE L.1*, SHARON E. BARTHOLOMEW-BEGAN1, and TATSUWO FURUKI2. 1Department of Biology, West Chester University, West Chester, PA, 19383, USA; 2Natural History Museum and Institute, Chiba 955-2 Aoba-cho, Chou-ku, Chiba-shi, Chiba 260-8682, Japan. - A preliminary overview of gemmae morphologies in Cavicularia densa Steph.
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