LEE, JI-YOUNG* and JOHN L. BOWMAN. Section of Plant Biology, University of California, Davis, CA 95616. - Reticulate evolution and reduction in stamen number within Lepidium L. (Brassicaceae).
Lepidium is a genus with about 175 species distributed
worldwide. Although the basic floral structure is conserved throughout
most of the Brassicaceae, there are many deviations within
Lepidium . Over half of Lepidium species have only two
medial stamens rather than four medial and two lateral stamens. And
one-eighth have four medial stamens and lack lateral stamens.
Furthermore, species with a reduced number of stamens tend to have
reductions in petal stature. Those species with reduced floral
structures are mostly native to the Americas and Australia. To
understand the frequency and evolutionary pathway of floral reduction,
PISTILLATA first intron sequences from 43 species were used
in phylogenetic analyses. The resulting gene tree suggests a
complicated history of reticulation within the American and derived
Australian Lepidium species. Based on the number of loci of
PITILLATA introns and known chromosome numbers, many New
World Lepidium species appear to be allopolyploids. An
artificial hybrid experiment demonstrated phenotypic dominance of
reduced stamen numbers. From genetic and molecular phylogenetic
studies, we propose a model in which the reduced stamen number
phenotype dominated in the New World Lepidium via
allopolyploid hybridization and subsequent speciation
Key words: Allopolyploid, Lepidium, PISTILLATA