AOBPreview originally published online on August 10, 2008
Annals of Botany 2008 102(4):643-651; doi:10.1093/aob/mcn140
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Floral and Inflorescence Morphology and Ontogeny in Beta vulgaris, with Special Emphasis on the Ovary Position
1 Instituto de Biología, Universidad Nacional Autónoma de México, Apdo. Postal 70-367, México D.F. CP 04510, México
2 National Herbarium of the Netherlands, Leiden University Branch, Leiden, The Netherlands
3 K.U. Leuven, Biology–Institute for Botany and Microbiology, Kasteelpark Arenberg 31, Heverlee (Leuven), Belgium
* For correspondence. E-mail alexander.vrijdaghs{at}bio.kuleuven.be
Received: 29 April 2008 Returned for revision: 27 May 2008 Accepted: 26 June 2008 Published electronically: 10 August 2008
Background and Aims: In spite of recent phylogenetic analyses for the Chenopodiaceae–Amaranthaceae complex, some morphological characters are not unambiguously interpreted, which raises homology questions. Therefore, ontogenetic investigations, emphasizing on ‘bracteoles’ in Atripliceae and flowers in Chenopodioideae, were conducted. This first paper presents original ontogenetic observations in Beta vulgaris, which was chosen as a reference species for further comparative investigation because of its unclarified phylogenetic position and its flowers with a (semi-)inferior ovary, whereas all other Chenopodiaceae–Amaranthaceae have hypogynous flowers.
Methods: Inflorescences and flowers were examined using scanning electron microscopy and light microscopy.
Key Results: Floral development starts from an inflorescence unit primordium subtended by a lateral bract. This primordium develops into a determinate axis on which two opposite lateral flowers originate, each subtended by a bracteole. On a flower primordium, first five tepal primordia appear, followed by five opposite stamen primordia. Simultaneously, a convex floral apex appears, which differentiates into an annular ovary primordium with three stigma primordia, surrounding a central, single ovule. A floral tube, which raises the outer floral whorls, envelops the ovary, resulting in a semi-inferior ovary at mature stage. Similarly, a stamen tube is formed, raising the insertion points of the stamens, and forming a staminal ring, which does not contain stomata. During floral development, the calyces of the terminal flower and of one of the lateral flowers often fuse, forming a compound fruit structure.
Conclusions: In Beta vulgaris, the inflorescence is compound, consisting of an indeterminate main axis with many elementary dichasia as inflorescence units, of which the terminal flower and one lateral flower fuse at a later stage. Floral parts develop starting from the outer whorl towards the gynoecium. Because of the formation of an epigynous hypanthium, the ovary becomes semi-inferior in the course of floral development.
Key words: Beta vulgaris, Chenopodiaceae, floral ontogeny, gynoecial development, epigynous hypanthium, semi-inferior ovary, inflorescence ontogeny, LM, SEM
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  Compiled by, F. Tooke, T. Chiurugwi, and N. Battey Flowering Newsletter bibliography for 2008 J. Exp. Bot., June 23, 2009; (2009) erp154v1. [Full Text] [PDF]
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