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Abstract Detail

Annonaceae evolution: integrating molecules, biogeography and ecology

Johnson, David M. [1], Stull, Gregory [2].

Growth architecture and phylogenetic constraint in the Annonaceae.

A recognized family characteristic of the Annonaceae is the distichous arrangement of the leaves. Growth architecture of the primary axis, however, is more variable, following one of two basic patterns: primary axis orthotropic with spiral phyllotaxis, or primary axis plagiotropic with distichous phyllotaxis. The former has been associated with the architectural model of Roux and the latter with the architectural model of Troll. The difference is manifested in the seedling stage, and is correlated with a difference in the orientation of the shoot apex: erect for the orthotropic axis, drooping for the plagiotropic axis. The two patterns have different phylogenetic distributions within the family: the basal genus Anaxagorea has the distichous arrangement, the Annonoideae show a non-reversing transition from spiral to distichous beginning with the split between Guatteria (spiral) and the remaining Annonoideae (distichous), and the Malmeoideae are virtually all spiral. The architecturally most diverse subfamily is the Ambavioideae, where some genera (Cananga, Cyathocalyx, Drepananthus, Lettowianthus, and Tetrameranthus) have the spiral arrangement and Cleistopholis and Mezzettia have the distichous arrangement; the subfamily is further architecturally remarkable for the spiral arrangement of the leaves on the secondary axes in Tetrameranthus, and the trend toward phyllomorphic branches in Drepananthus. Architecture pattern for a number of genera in key phylogenetic positions is, however, still unknown, and in others should be assessed in a wider range of species. Polyalthia, for example, even in its recently restricted circumscription, has shown unexpected variability: “normal” spiral arrangement of branches (P. cauliflora, P. cinnamomea, P. suberosa), species with distichous arrangement (P. bullata), and even species in which the secondary axes do not form and the plant has a palmlike unbranched trunk with only spiral phyllotaxis (P. insignis). The stability of the two architecture types over large clades suggests either phylogenetic “constraint” to the pattern at a molecular level, or different kinds of ecological situations to which each pattern is suited. Studies examining gene regulation of auxin flux in the shoot apex might address the former, and experimental studies of seedling establishment and growth under different ecological conditions would inform the latter.

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2 - University of Florida, Florida Museum of Natural History, PO Box 117800, Gainesville, FL, 32611, USA


Presentation Type: Symposium or Colloquium Presentation
Session: SY04
Location: Pines South/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 11:00 AM
Number: SY04007
Abstract ID:464
Candidate for Awards:None

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