Journal Article

Floral and Inflorescence Morphology and Ontogeny in <i>Beta vulgaris</i>, with Special Emphasis on the Ovary Position

Hilda Flores Olvera, Erik Smets and Alexander Vrijdaghs

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 102, issue 4, pages 643-651
Published in print October 2008 | ISSN: 0305-7364
Published online August 2008 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcn140
Floral and Inflorescence Morphology and Ontogeny in Beta vulgaris, with Special Emphasis on the Ovary Position

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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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.

Keywords: Beta vulgaris; Chenopodiaceae; floral ontogeny; gynoecial development; epigynous hypanthium; semi-inferior ovary; inflorescence ontogeny; LM; SEM

Journal Article.  5127 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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