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Orchid Biology: Darwin`s Contrivances 150 Years Later

Buitrago Delgado, Elsy [1], Cameron, Kenneth [2].

The Power of Movement in Orchids, a Phylogenetic Study of Porroglossum (Pleurothallidinae) .

Charles Darwin was fascinated by the power of movement in plants, and even wrote a book with that very title. Climbing vines, leaves exhibiting sleep movements, and insectivorous plants with fast-action snap-traps were of special interest to him. Within Orchidaceae Darwin called Catasetum, "the most remarkable of all orchids," undoubtedly because of the well known manner in which male flowers of the genus eject their pollinaria in response to a physical stimulus. Had Darwin known of the orchid genus Porroglossum, he surely would have been equally enthralled. These small plants of subtribe Pleurothallidinae are native to the cloud forests of the Andes, where ca. 50 species in the genus have been discovered. All are sympodial with a creeping habit, and with unifoliate stems lacking pseudobulbs. In some cases the leaves are warty, coriaceous, purple, or may exhibit an iridescent blue color. The flowers, however, are what set Porroglossum apart from nearly all other orchids. When stimulated by an insect or other external force, the labellum of these orchids lifts upward, quite rapidly in some species, in order to trap pollinators against the column. Depending upon the species, the floral trap resets itself after a matter of minutes or hours. Phylogenetic relationships within Porroglossum are unknown, but the genus has been variously treated taxonomically. Luer (1987) divided the genus in two subgenera, Eduardii and Porroglossum, the first with just 2 species and the latter divided into three sections: Echidna (2 species), Porroglossum (12 species)and Tortae (4 species), but not all of the species in the genus were considered at that time. Years later Aubron (2005) divided the genus into four subgenera: Eduardii (2 species), Echidna (3 species), Tortae (8 species) and Porroglossum (22), with the latter divided into three sections: Brevisepala (9 species), Porroglossum (11 species) and Mordax (2 species). We have reconstructed the phylogeny of Porroglossum and appropriate outgroups using a combination of nuclear ribosomal ITS, and plastid psbA- trn-H, trnL-F, and ycf1 sequences from nearly all species in the genus. Results will be discussed, and implications for classification and understanding the evolution of Porroglossum's unique floral "behavior" will be noted.

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1 - Northwestern University, Dept of Molecular Bioscience, 2205 Tech Drive, Evanston, IL, 60208, USA
2 - University of Wisconsin-Madison, Dept of Botany, WI State Herbarium, Birge Hall, 430 Lincoln Dr., Madison, WI, 53706, USA

Keywords:
Orchidaceae
Andes
Darwin
pollination.

Presentation Type: Symposium or Colloquium Presentation
Session: C6
Location: Franklin B/Hyatt
Date: Wednesday, July 11th, 2012
Time: 4:00 PM
Number: C6010
Abstract ID:296


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