The palm family (Arecaceae): a microcosm of sexual system evolution

Abstract

Among the 416 angiosperm families, palms (Arecaceae) are striking in possessing almost all possible combinations of hermaphroditic and/or unisexual flowers, making them a particularly interesting subject for studies of the evolution of plant sexuality. The purpose of this review is to highlight the amazing diversity of sexual expression in palms with a view to proposing scenarios to explain the evolution of this character, drawing on the numerous advances that have been made over the last 20 years in palm systematics, ecology, developmental biology, phylogenetics and genomics. We provide an overview of the variability of sexual expression in palms, with illustrations of the associated morphological diversity and its significance to reproduction. We discuss the evolution of sexual systems using the most recent phylogenetic framework available for palms. Finally, we review advances made towards unravelling the genetic basis of sexual expression in palms. Our survey opens new perspectives for understanding how plant sexuality has evolved in angiosperms as a whole.

Young sex chromosomes in plants and animals

“…Genetic data show that mutations in distinct genes are involved in several plants where relevant information can be obtained. Examples where the ancestor was probably monoecious include Ecballium (Cucurbitaceae) and spinach (Amaranthaceae), Sagittaria latifolia (Alismataceae), and the date palm genus Phoenix (Westergaard, ; Dorken & Barrett, ; Nadot et al ., ; Torres et al ., ; Wadlington & Ming, ). There is also good evidence for the involvement of two distinct genes in at least two species where dioecy appears to have evolved from hermaphroditism: Silene latifolia , based on the phenotypic effects of deletions of Y‐linked regions (Westergaard, ; Kazama et al ., ), and A. officinalis , in which genome sequencing yielded candidate male‐sterility and female‐suppressing genes (Harkess et al ., , ).…”

Palms - emblems of tropical forests

“…Twenty‐five years and 90 scientific publications later, it was confirmed that palms are indeed insect pollinated, exhibit a range of adaptations and mechanisms and that beetles are the most important pollinators of palms (Barfod, Hagen & Borchsenius, ). Studies of palm pollination have continued to attract the attention of palm biologists and the latest overview emphasizes the diversity and evolution of the many sexual systems in palms (Nadot et al ., ). The diversity of reproductive systems and the intricate palm–insect interactions have inspired several more detailed studies of single systems.…”

Sex change in the dioecious palm Ceroxylon quindiuense (Arecaceae)

“…In dioecious plants, those in which individuals are either male or female, sex change is also uncommon, and it has never been recorded in palms, one of the groups of plants with the broadest diversity of sexual systems (Nadot et al. ). We recently observed two cases of sex change in the dioecious Quindío wax palm, Ceroxylon quindiuense , the world's tallest palm and an umbrella species of Andean forests (Bernal and Sanín ), and Colombia's National Tree.…”

“…Sexual expression in palms includes hermaphroditic, polygamous, monoecious, temporally dioecious, and strictly dioecious species (Nadot et al. ). Only five genera are known to alternate male and female inflorescences in the same plant: Arenga (subfamily Coryphoideae), Lepidorrhachis, Wettinia, Marojejya and Elaeis (subfamily Arecoideae) (Baker and Hutton ).…”

“…Dioecy has evolved several times among palms (Nadot et al. ), and dioecious species occur in four of the five subfamilies of Arecaceae. Thus, the mechanisms determining dioecy may differ among genera.…”