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Abstract Detail


Developmental and Structural Section

Marazzi, Brigitte [1], Conti, Elena [1], Endress, Peter K. [1].

Evolution of floral diversity in the buzz-pollinated genus Senna (Leguminosae, Cassiinae).

THE large genus Senna (Leguminosae, Cassiinae) displays several floral traits related to buzz pollination, including poricidal anther dehiscence and heteranthery, but also enantiostyly and asymmetry of the corolla and androecium. Almost nothing is currently known about the structure and evolution of these traits in Senna. Therefore, we performed structural studies on the androecium and corolla, in particular on the diversity and development of stamens and petals. Anthers have variably long beaks, especially in the abaxial stamens they are long (up to several millimeters) and tubular. We found different kinds of anther-tip differentiation. In the least differentiated case, each theca has a pore, and pollen is released from the pore of this theca. In other cases, the apical part of the two thecae forms a shared chamber, and pollen traverses this chamber and is released through two separate pores or one confluent pore. Long anther beaks elongate late in development, whereas the dehiscence area that results in the pore is formed earlier. The shared chamber and the canals to the pores are formed by decay of the tissue in the sterile anther tip. Filaments of the middle stamens and of the staminodes are united in S. tonduzii. There is also much diversity in petal shape and venation; especially in asymmetric flowers, the upper petals are more or less reduced and the lower petals are strongly modified in size, shape and venation. Prominent floral asymmetry is expressed early in development. In strongly modified petals venation is particularly robust. Most Senna species have three main petal veins, but a few species of the basal lineages of the genus and Cassia, the sister of Senna, have only one main vein. We will discuss the implications of our findings for our current work on floral evolution in Senna.


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1 - Universität Zürich, Institut für Systematische Botanik, Zollikerstrasse 107, Zürich, CH-8008, Schweiz

Keywords:
Senna
Caesalpinioideae
Buzz pollination
Floral symmetry
development
corolla
stamen fusion
androecium
poricidal dehiscence
Cassia
floral evolution.

Presentation Type: Oral Paper:Papers for Sections
Session: 2-4
Location: 303/Bell Memorial Union
Date: Monday, July 31st, 2006
Time: 8:45 AM
Abstract ID:119


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