AOBPreview originally published online on June 28, 2006
Annals of Botany 2006 98(3):619-630; doi:10.1093/aob/mcl138
The Floral Scales in Hellmuthia (Cyperaceae, Cyperoideae) and Paramapania (Cyperaceae, Mapanioideae): An Ontogenetic Study
1 Laboratory of Plant Systematics, Institute of Botany and Microbiology, K.U.Leuven, Kasteelpark Arenberg 31, B-3001 Leuven, Belgium, 2 Research Group Spermatophytes, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium, 3 National Herbarium of The Netherlands, Leiden University Branch, PO Box 9514, NL-2300 RA Leiden, The Netherlands and 4 Botany Department, University of Cape Town, 7701 Rondebosch, South Africa
* For correspondence. E-mail alexander.vrijdaghs{at}bio.kuleuven.be
Received: 12 April 2006 Returned for revision: 9 May 2006 Accepted: 19 May 2006 Published electronically: 28 June 2006
• Background and Aims In 1976 the monotypic genus Hellmuthia was placed in the Hypolytreae s.l., but was subsequently ascribed to the Mapanioideae, tribe Chrysitricheae, mainly because of the presence in Hellmuthia of two lateral, mapanioid-like floral scales with ciliated keels, the anatomy of the nutlet, the embryo and the inflorescence. Recently, based on cladistic analyses and supported by pollen ontogenetic evidence, Hellmuthia was transferred to a Cyperaceae, tribe Cypereae, clade mainly consisting of Ficinia and Isolepis. In this study, the floral ontogeny in Hellmuthia was investigated and compared with the floral ontogeny in Paramapania, with special attention for the floral scales.
• Methods Freshly collected inflorescences of Hellmuthia membranacea and Paramapania parvibractea were investigated using scanning electron and light microscopy.
• Key Results In the conical ‘spikelet’ in Hellmuthia, proximal bracts occur, each axillating an axis with empty glume-like structures, or a reduced spikelet. Hence, it is a reduced partial inflorescence. In Hellmuthia, the stamen primordia originate before the primordia of the perianth–gynoecium appear. Moreover, a third adaxially positioned ‘floral scale’ was observed for the first time. The position and relative time of appearance of the floral scales in Hellmuthia are typical for perianth parts in Cyperoideae. The basal position of Hellmuthia within a clade of species with usually perianthless flowers, allows the presence of rudiments of a perianth in Hellmuthia to be interpreted as a primitive state. Development of the lateral ‘scales’ in Paramapania follows a different pattern. Therefore, it was decided that the lateral ‘scales’ in Paramapania are different from the lateral perianth parts in Hellmuthia. The pollen grains in Hellmuthia are cyperoid, with one polar and five lateral apertures, of which the membrane is covered with sexinous bodies. The pollen surface is granulate and perforate with microspines.
• Conclusions The floral ontogeny in Hellmuthia occurs according to the general cyperoid pattern. The lateral scales in Hellmuthia are perianth parts, and they are not homologous to the lateral ‘scales’ in Paramapania.
Key words: Floral scales, Paramapania, floral ontogeny, Cyperaceae, Hellmuthia, SEM, homology
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