DOUGLAS, ANDREW W. The Botany Department, The Field Museum, Roosevelt Rd at Lake Shore Drive, Chicago, IL 60605. - Evolutionary patterns among species of Labichea, a caesalpinioid legume.
The Australian Labichea comprises 14 species in the subtribe
Labicheinae (Cassieae). Different species are geographically isolated
from one another and are found in the east, north, west, and southwest
of Australia. Members of the genus are characterized by the presence
of two fertile anthers in the adaxial-antesepalous sites of the flower
and distichous inflorescences-- putative synapomorphies separating
them from their sister-genus Petalostylis. Morphological
variation among species of Labichea include changes in inflorescence
architecture, degree of floral symmetry and anther morphology. In ten
species, the two anthers are morphologically different from one
another (heteromorphic: one anther is elongate and porate; the other
is shorter, wider and has either porate or small lateral slits at the
base or top of the anther). In the other four species, each of the
two anthers in a flower are essentially similar (isomorphic
androecium). Both conditions are associated with architectural
differences in the inflorescence and in pollination strategies (e.g
pendulum symmetry on the inflorescence). In this study, cladistic
hypotheses of relationship based on morphological and gene sequence
data are used to examine the patterns of distribution and change among
several of the reproductive features. The resultant cladograms based
on mature morphological characters provide a different interpretation
of androecial evolution than the cladogram from the molecular data.
The former implies that the heteromorphic androecium has been derived
twice from the plesiomorphic isomorphic condtion. Molecular evidence
implicates the heteromorphic anthers as the plesiomorphic condition in
the genus, the isomorphic condition having been derived three times. .
These transformational hypotheses and other hypotheses of
morphological divergence are subsequently examined in a comparative
ontogenetic study. Preliminary developmental evidence supports the
transformation hypothesis from the molecular data.
Key words: anther evolution, Caesalpinioideae, Fabaceae, Labichea, phlogeny