SCHUETTE, SCOTT W. Department of Plant Biology, Southern Illinois University, Carbondale IL 62901-6509. - Morphology of the simple thalloid liverwort Jensenia Lindb. (Pallaviciniaceae).
Jensenia is a dioicous, dendroid liverwort which superficially
resembles some species of Pallavicinia. In fact,
Jensenia is sometimes regarded as but a subgenus of
Pallavicinia. However, several morphological features viewed
with SEM clearly distinguish Jensenia from all other genera of
the Pallaviciniaceae. This study looks at representatives of the
twelve species of Jensenia, focusing on those unique features
that separate it from Pallavicinia. Preliminary investigations
of Jensenia erythropus, from Venezuela, reveal that the thallus
arises from a dark red to purplish, underground rhizome that is
covered with unicellular rhizoids. The thallus wing margin is devoid
of slime hairs and the apices are deeply incised in male and female
plants. Optical microscopy shows there is a prominent midrib that is
one-third to one-half the thallus width that dichotomously branches in
correlation with thallus furcations. The antheridia are reddish and
wholly cover the midrib, unlike Pallavicinia where they are in
parallel rows on both sides of the midrib. The archegonia are
restricted to the dorsal surface at the basalmost furcation, which is
different from the scattered arrangement seen in Pallavicinia,
and are surrounded by a slightly elevated, laciniate perichaetium. The
pseudoperianth, which may be more aptly called a caulocalyx, is long
and cylindrical. The spores are approximately 25-40µm in diameter with
a broadly pilate wall anastomosing at the pilae heads. The
thick-banded elaters are bispiral and extremely long at ca. 300µm. At
maturity the ellipsoid capsule appears to have a bistratose wall,
becoming tri-to multi-stratose at the apex.
Key words: liverwort, morphological features, optical microscopy, SEM