Developmental and Structural Section
Marazzi, Brigitte , Endress, Peter K. .
Diversity, development and evolution of asymmetric flowers in Senna (Leguminosae).
The buzz-pollinated genus Senna (Leguminosae) includes both species with monosymmetric and with diverse asymmetric, enantiomorphic (enantiostylous) flowers, with left and right morphs on the same plant. To assess homology of the patterns of floral asymmetry, we studied flower structure of species from all major clades of Senna, and development of four enantiomorphic species from different major clades. The asymmetry morph of a flower is correlated with the direction of spiral calyx aestivation (clockwise: right morph; counter-clockwise: left morph). We recognized five major patterns of floral asymmetry, resulting from different combinations of at least six structural elements: (1) deflection of the carpel; (2) deflection of the median abaxial stamens; (3) deflection of one lateral abaxial stamen or, rarely, (4) modification in size of this stamen; and modification in shape and size of (5) one or (6) both lower petals. Petals have diverse venation: most Senna species have three main petal veins, a few species of the basal lineages of Senna, and also Cassia (sister to Senna, have only one main vein. Expression of floral asymmetry during development differs among floral whorls. Prominent corolla asymmetry begins in early bud (unequal development of lower petals). Androecium asymmetry begins in mid-stage bud (unequal development of thecae in median abaxial stamen; twisting of androecium) or at anthesis (stamen deflection). Gynoecium asymmetry begins in early bud (primordium appearing off the median plane; ventral slit laterally oriented) or mid-stage to late bud (carpel deflection). In both monosymmetric and highly asymmetric corollas of enantiostylous flowers, pronouncedly concave and robust petals likely function to ricochet pollen flow and to reduce loss of pollen during buzz pollination. Preliminary ancestral character state reconstructions moderately support the hypothesis that the carpel was not deflected in ancestral Senna flowers, but strongly support that asymmetric androecium and corolla evolved from enantiostylous flowers.
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1 - Universität Zürich, Institut für Systematische Botanik, Zollikerstrasse 107, Zürich, CH-8008, Schweiz
Presentation Type: Oral Paper:Papers for Sections
Location: Boulevard C/Hilton
Date: Tuesday, July 10th, 2007
Time: 8:30 AM