Systematics/Phytogeography / Taxonomie/ Section
Prenner, Gerhard , Klitgaard, Bente .
Towards unlocking the deep nodes of Leguminosae: Floral development and morphology of the enigmatic Duparquetia orchidacea.
Duparquetia orchidacea (Caesalpinioideae-Cassieae-Duparquetiinae) is a monotypic genus from tropical W Africa. Phylogenetic studies based on molecular and morphological characters, respectively, resolved D. orchidacea, albeit with very weak support, to an isolated position among the early branching Leguminosae. This corresponds with its unique pollen morphology and its unusual, zygomorphic, orchid-like flowers. Floral morphology and development were studied using SEM. There is no overlap in the formation of the four organ whorls. All floral organs are formed in a continuous, acropetal sequence. Only four sepals are formed, the fifth completely lost. This is probably due to long plastochrons (i.e. time intervals) between sepals one to three. A gap on one side of the adaxial sepal is interpreted as the position of the lost sepal. Late in development the inner lateral sepal becomes bi-lobed. Five petals are formed in a rapid succession. The median adaxial petal soon becomes the outermost. The last initiated petal, either the left or right abaxial one, becomes the innermost. The petals are followed by four stamens which form a synadrium of four anthers with porate openings. The fifth, abaxial stamen from the outer whorl and the entire inner stamen whorl are completely lost. A single superior ovary is formed, from this develops a woody, elastically dehiscent pod typical of many caesalpinioid legumes. The tip of the young carpel points either to the left or right. Its direction depends on the position of the last formed petal. Comparison with related caesalpinioid taxa, e.g. Tamarindus indica, with similar floral bauplan, shows that it differs remarkable from D. orchidacea in both floral structure and timing of organ initiation. The differences between D. orchidacea, T. indica, and other related caesalpinioid genera will be further explored; and implications of these differences for the systematics of the basally branching Leguminosae will be discussed.
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1 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Surrey, TW9 3AB, United Kindom
2 - Natural History Museum, Department of Botany, London, SW7 5BD, United Kingdom
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 8:15 AM