Abstract

Fleshy structures associated with the ovule/seed arose independently several times during gymnosperm evolution. Fleshy structures are linked to ovule/seed protection and dispersal, and are present in all the four lineages of extant gymnosperms. The ontogenetic origin of the fleshy structures could be different, and spans from the ovule funiculus in the Taxus baccata aril, the ovule integument in Ginkgo biloba, to modified bracts as in case of Ephedra species. This variability in ontogeny is reflected in the morphology and characteristics that these tissues display among the different species. This review aims to provide a complete overview of these ovule/seed-associated fleshy structures in living gymnosperms, reporting detailed descriptions for every genus. The evolution of these independently evolved structures is still unclear, and different hypotheses have been presented—protection for the seeds, protection to desiccation—each plausible but no one able to account for all their independent origins. Our purpose is to offer an extensive discussion on these fleshy structures, under different points of view (morphology, evolution, gene involvement), to stimulate further studies on their origin and evolution on both ecological and molecular levels.

摘要

在裸子植物进化过程中，与胚珠/种子相关的肉质结构多次独立出现。肉质结构与胚珠/种子保护和传播有关，并且存在于现存裸子植物的所有四个谱系中。肉质结构的个体发育起源可能不同，从红豆杉中的胚珠索、银杏中的胚珠珠被，到麻黄中的改良苞片物种。个体发育的这种可变性反映在这些组织在不同物种之间显示的形态和特征上。本综述旨在全面概述活裸子植物中这些胚珠/种子相关的肉质结构，报告每个属的详细描述。这些独立进化的结构的进化仍不清楚，并且已经提出了不同的假设——保护种子、保护干燥——每一种都有可能，但没有人能够解释它们所有的独立起源。我们的目的是在不同的观点（形态学、进化、基因参与）下对这些肉质结构进行广泛的讨论，以刺激在生态和分子水平上对其起源和进化的进一步研究。