Ultrastructure du tectum de pollens d'Ombellifères

Abstract

A l'intérieur de la famille des Ombellifères, deux types de tectum complet ont été observés: un tectum simple lorsqu'il constitue une strate homogène au dessus des columelles; un tectum structuré lorsqu'il forme une strate hétérogène au dessus des columelles (columelles tectales d'ordre 2, tectum externe et tectum interne distincts …). Un essai de compréhension de ces structures en rapport avec l'évolution de la famille et la biogéographie est donné. The tectum of the family Umbelliferae, which is a complete tectum, shows two types of structure. The first type is a simple tectum: the columellae with globular heads are either quite distinct or fused by 2 or 3 into short arches (Artedia); the arches may be longer, forming a striate-reticulate sculpture with perforations (Daucus). The second type is a structured tectum; it is formed either by columellae heads arranged on different levels (Vanasushava, Aphanopleura, Cuminum, Trachymene: except for Vanasushava, the outermost level may be assimilated to an outer tectum, the other levels to an inner tectum) or by small intra-tectal columellae, supported by infra-tectal columellae, much bigger (Turgenia). A tentative explanation of these structures in relation to both evolution in the family and biogeographic conditions is tried.