Spikelet structure and development in Cyperoideae (Cyperaceae): a monopodial general model based on ontogenetic evidence |
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Authors: | Alexander Vrijdaghs Marc Reynders Isabel Larridon A. Muthama Muasya Erik Smets Paul Goetghebeur |
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Affiliation: | 1Laboratory of Plant Systematics, Institute of Botany & Microbiology, K.U. Leuven, Kasteelpark Arenberg 31, B-3001 Heverlee (Leuven), Belgium;2Research Group Spermatophytes, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium;3University of Cape Town, Department of Botany, Private Bag, 7700 Rondebosch, South Africa;4National Herbarium of the Netherlands, Leiden University Branch, Leiden, The Netherlands |
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Abstract: | Background and AimsIn Cyperoideae, one of the two subfamilies in Cyperaceae, unresolved homology questions about spikelets remained. This was particularly the case in taxa with distichously organized spikelets and in Cariceae, a tribe with complex compound inflorescences comprising male (co)florescences and deciduous female single-flowered lateral spikelets. Using ontogenetic techniques, a wide range of taxa were investigated, including some controversial ones, in order to find morphological arguments to understand the nature of the spikelet in Cyperoideae. This paper presents a review of both new ontogenetic data and current knowledge, discussing a cyperoid, general, monopodial spikelet model.MethodsScanning electron microscopy and light microscopy were used to examine spikelets of 106 species from 33 cyperoid genera.ResultsOntogenetic data presented allow a consistent cyperoid spikelet model to be defined. Scanning and light microscopic images in controversial taxa such as Schoenus nigricans, Cariceae and Cypereae are interpreted accordingly.ConclusionsSpikelets in all species studied consist of an indeterminate rachilla, and one to many spirally to distichously arranged glumes, each subtending a flower or empty. Lateral spikelets are subtended by a bract and have a spikelet prophyll. In distichously organized spikelets, combined concaulescence of the flowers and epicaulescence (a newly defined metatopic displacement) of the glumes has caused interpretational controversy in the past. In Cariceae, the male (co)florescences are terminal spikelets. Female single-flowered spikelets are positioned proximally on the rachis. To explain both this and the secondary spikelets in some Cypereae, the existence of an ontogenetic switch determining the development of a primordium into flower, or lateral axis is postulated. |
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