Fleshy Structures Associated with Ovule Protection and Seed Dispersal in Gymnosperms: A Systematic and Evolutionary Overview

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.

Morpho‐palynological investigation of gymnospermal flora from subalpine and alpine zones of northern Pakistan using LM and SEM

“…He noticed the sexine finely reticulate with OL‐pattern (Dong et al, 2020). Nigris, D'Apice, Moschin, Ciarle, and Baldan (2021) have given the equatorial diameter 12.2 (10–14) μm and polar diameter 9 (7–11) μm which differ from the present finding.…”

The role of pollination in controlling Ginkgo biloba ovule development

“…These results indicate that this switch is triggered by pollination, long before fertilization. Indeed, the seed coat of G. biloba is characterized by the differentiation in an outer and fleshy sarcotesta, characterized by the presence of fatty acids, among which butyric acid confers a foul odour to the seed, and in an inner sclerotesta, that constitutes the lignified layer protecting the inner female gametophyte and/or embryo (Singh et al ., 2008 ; Nigris et al ., 2021 ). During the switch from pre‐pollination to postpollination stages the metabolic pathways required for the biosynthesis of butanoate (the ester of butyric acid) and fatty acids are significantly enriched together with transcriptional activators of the lignin biosynthesis.…”

Development of the seed-cones Taxus canadensis in culture (Tsytsin Main Botanical Garden RAS, Moscow, Russia)

“…A comprehensive study of the de ve lopment of seeds and their fleshy appendages has not been carried out. This study is also relevant due to the fact that the causes of the appearance of fleshy structures in Gym no sperm cones have not yet been established and are of interest to modern researchers (Nigris et al 2021). At this time, as a result of studying the development of dry fruits, the seeds of which have arils, the functions of arils, and reasons for the appearance of arils and their fixation in the process of evolution were proposed (Trusov 2016(Trusov , 2021.…”