Developmental and Structural Section
Oskolski, Alexei A. , Sokoloff, Dmitry D , Plunkett, Gregory , Lowry, Porter P. II .
The flower of Plerandra (Araliaceae): a unique case of a polycyclic androecium within derived euasterids.
Molecular evidence has demonstrated that the genus Plerandra belongs to the Melanesian Schefflera clade of Araliaceae. Most species of this clade have pentamerous flowers, but members of Plerandra and the closely related subgroup “Dictyophlebes” show an increase in the number of androecium whorls from one to seven, together with a multiplication of stamens within each whorl. Consequently, flowers of P. pickeringii may contains >500 stamens (the largest number known among euasterids). To explore the evolution of this condition, floral development in six species of Plerandra and one of “Dictyophlebes” was studied and compared. Results demonstrate a remarkable feature in which the receptacle is concave and cup-like. The calyx is pentamerous, with the sepal bases united to form a short tube. The corolla is initiated as five bulges united basally into a low ring, and as it develops it appears to comprise free, valvate petals. In the species examined, the flowers bear 1-5 stamen whorls and the number per whorl varies from 20-25 to 50-60. Initiation of new whorls proceeds on the concave receptacle in a basipetalous (i.e., morphologically centripetal) sequence; the stamen primordia of a given whorl arise simultaneously. The gynoecium consists of 6-14 carpels initiated as horseshoe-shaped primordia on the concave receptacle. Once initiated, the plicate parts of the carpels grow towards the flower center, with their ventral margins facing downward. Later in development, the ventral sides (with stigmatic tissue) turn upwards and outwards due to intercalary elongation. The ascidiate parts of the carpels undergo intercalary growth well after initiation of the plicate parts. Thus, the androecium of these plants shows a unique case of primary polycycly (sensu Ronse De Craene & Smets), and polyandry seems to have arisen from a monocyclic pentamerous condition. The formation of a concave receptacle appears to be a prerequisite for the expression of these features as well as of the peculiar mode of gynoecial development observed in Plerandra and “Dictyophlebes”.
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1 - Komarov Botanical Institute, Botanical Museum, Prof. Popov str. 2, St.Petersburg, 197376, Russia
2 - Moscow State University, Department of Higher Plants, Biological Faculty, 119992, Moscow, Russia
3 - New York Botanical Garden, Cullman Program for Molecular Systematics Studies, 200th Street and Kazimiroff Boulevard, Bronx, New York, 10458, USA
4 - Missouri Botanical Garden, Africa & Madagascar Department, P.O. Box 299, St. Louis, MO, 63166-0299, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 551A/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 11:00 AM