CANNE-HILLIKER, JUDY1*, TOM HAZLE2, and LARA YACOB3. 1Department of Botany, University of Guelph, Guelph, Ontario, Canada, N1G 2W1; 2Department of Biology, University of Ottawa, Ottawa, Ontario, Canada, K1N 6N5; 3United Nations, 303 E. 45th St., New York, N. Y. 10017. - Ontogeny and phylogeny of the Erythranthe clade of Mimulus (Scrophulariaceae s. l.) and Myoporaceae.
Comparative investigations of floral ontogeny among populations,
species and genera provide data about the generation of floral
diversity among taxa when recently proposed phylogenies exist for the
taxa. These studies also allow formation of hypotheses regarding
ontogenetic changes that accompany evolutionary divergence. The
Erythranthe clade of Mimulus has been the subject of
much systematic, genetic and phylogenetic study. Mimulus
cardinalis is one of four species in this small clade that are
hummingbird-pollinated. Its sister species, M. lewisii, is
bee-pollinated. Within M. cardinalis, populations differed in
size and shape of floral apices at initiation of sepal primordia, and
in timing of organ differentiation and enlargement. Interracial
differences occurred among populations of M. lewisii during
corolla and pistil differentiation and enlargement. Allometric
analyses using index variables showed that the abaxial corolla wall
and stamen pair, as well as the style, differed in rate and duration
of growth among populations of M. cardinalis, and between the
races of M. lewisii. Within buds, differences in rates of
growth between the adaxial and abaxial corolla regions and stamen
pairs yielded the floral forms suited to hummingbird-pollination and
bee-pollination. Architectural differences involving the stamens and
corolla throats also characterized species. In another investigation,
comparison of representative species of genera of Myoporaceae revealed
that genera differed in sequence of initiation of calyx and corolla
primordia, as well as differentiation and enlargement of sepals and
petals. These different ontogenies resulted in bilateral, bilabiate,
and pseudoactinomorphic mature forms. Order of stamen enlargement
varied among taxa as did stamen number, lengths, and positions
relative to the corolla and pistil. However, the style consistently
curved to one side of the median plane during late ontogeny.
Hypotheses of ontogenetic changes among taxa were proposed with the
aid of recent phylogenies generated by other workers for
Mimulus and Myoporaceae.
Key words: Mimulus, Myoporaceae, ontogeny, phylogeny, Scrophulariaceae