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Reproductive structures in palms (Arecaceae) : evolution of sexual system and stamen number

Thesis

French

ID: <10670/1.4tpiih>

Abstract

Palms (Arecaceae) are an emblematic family of monocots of 183 genera and around 2500 species distributed on all continents, throughout tropical and subtropical areas. Their characteristic leaves and stems make palms immediately recognizable in the field. The inconspicuous palm flowers are usually considered as rather dull. They are usually small (a few centimetres), trimerous, often unisexual, colourless (white or greenish) and grouped into huge inflorescences. However palms exhibit a large diversity in sexual system and in stamen number, diversity that is still poorly understood. The three main sexual systems of angiosperm, hermaphroditism, dioecy and monoecy are present in palms. Stamen number ranges between a few units (oligandry) to several dozens and even several hundreds of units (polyandry) in some genera. We studied the evolution of sexual system and stamen number at the family level. We used as historical framework a well-supported and dated phylogeny, published recently. Our study showed that the putative ancestor of palms was monoecious and bore oligandrous flowers with 6 stamens. From these ancestral states, several transitions occurred: towards hermaphroditism and dioecy and towards polyandry respectively. In order to initiate a research on a possible functional significance of increase in stamen number, we investigated the relationship between stamen number and pollen production, by extracting the total pollen content from flowers of 82 species. Our study showed a tendency towards higher pollen production when the number of stamen increases in two subfamilies. We also produced molecular phylogeny of a subtribe (Ptychospermatinae) in which the range of variation in stamen number is exceptional. Further investigations into genetic, developmental, ecology and pollination biology are needed.

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