Ecological and phylogenetic constraints determine the stage of anthetic ovule development in orchids

Abstract

Premise Unlike most flowering plants, orchid flowers have under‐developed ovules that complete development only after pollination. Classical studies reported variation in the stage in which ovule development is arrested, but the extent of this variation and its evolutionary and ecological significance are unclear. Methods Here, we used light microscopy to observe ovule development at anthesis for 39 species not previously studied and surveyed the literature gaining information on 94 orchid species. Tropical and temperate members of all five orchid subfamilies as well as species with contrasting pollination strategies (rewarding versus deceptive) and life forms (epiphytic versus terrestrial) were represented. We analyzed the data using statistical comparisons and a phylogenetic generalized least square (PGLS) analysis. Results Apostasioideae, the sister to the rest of the orchids, have mature ovules similar to other Asparagales, while under‐differentiated ovules are present in the other subfamilies. Ovule developmental stages showed high variation even among closely related groups. Ovules were more developed in terrestrial than in epiphytic, in temperate than in tropical, and in rewarding than in deceptive pollination orchid species. This latter comparison was also significant in the PGLS analysis. Conclusions These results suggest that ovule developmental stage in orchids can be shaped by ecological factors, such as seasonality and pollination strategy, and can be selected for optimizing female reproductive investment.

Apomixis beyond trees in the Brazilian savanna: new insights from the orchid Zygopetalum mackayi

“…Contrary to other angiosperms, the endosperm in orchid seeds is non-functional, as it is never formed or degenerates after polar nuclei fertilization (Yeung 2017). Therefore, male sexual function must be conserved in orchids not for endosperm formation, but because pollination is necessary for ovule development (Mayer et al 2021).…”