Flower biology of the cactus Coryphantha elephantidens in the tropical dry forest of Central Mexico

Abstract

Floral traits and sexual systems in angiosperms are strategies that enhance outcrossing within hermaphrodite flowers and among individuals in a population. Sexual systems with unisexual flowers have also evolved among angiosperms, resulting in sex specialization. Furthermore, the interaction of floral traits and floral visitors determines successful plant reproduction. Globose cacti are bee pollinated, and variation in the diversity of their pollinator assemblages is strongly associated with floral phenotype. Our objective was to describe the floral biology of the cactus Coryphantha elephantidens and to determine its relationship with pollinators. Floral traits were studied by direct observations in live and fixed flowers. The breeding system was determined using two estimators based on floral morphology: pollen grains to ovules per flower (P/O) ratio and outcrossing index. Pollination treatments were conducted to determine the mating system. Floral visitors were recorded using direct observation. Flowers of C. elephantidens are variable in color, protandric, herkogamous and nectarless. Estimators of the breeding system indicated xenogamy, which is consistent with the obligate outcrossing revealed by the pollination experiment. Thirty‐seven percent of the plants have female flowers that do not produce pollen, making this population functionally gynodioecious. Both fruit and seed set were high compared to other globose cacti. Pollinators included eight species of native bees, a more diverse pollinator assemblage than other globose cacti. Given the high pressure on pollen due to functional gynodioecy, nectarless flowers, an outcrossing mating system, and the necessity of pollinators to set seeds, we concluded that native bees are highly efficient pollinators that play a crucial role in the sexual reproduction of C. elephantidens.

Variability in mating strategies in a widespread cactus in the Chihuahuan Desert

“…The length of the style of each flower and one filament per flower were measured with a digital Vernier caliper to the nearest 0.01 mm. If, by means of a paired t‐test, the length of both floral structures were significantly different, we confirmed herkogamy (Martínez‐Peralta and Martínez‐Zavala 2020).…”

“…Some floral traits differ between the self‐incompatible population of MBR and the self‐compatible population of CR. First, some flowers at MBR open for more than one day, a trait observed in some self‐incompatible cacti that minimizes the risk of reproductive failure due to insufficient pollination rates and increases the chances of mating with more individuals (del Castillo and González‐Espinosa 1998, Bustamante and Búrquez 2008, Martínez‐Peralta and Martínez‐Zavala 2020). Another remarkable difference is the presence of herkogamy in the flowers of the MBR population, which was absent in the CR population (Mandujano et al 2013).…”

Comparative nectar dynamics in four ornithophilous Melocactus (Cactaceae) species in a seasonally dry tropical forest

“…Given that nectar is an aqueous solution, its production is highly dependent on the availability of water during the flowering period (Petanidou et al, 2008). Climatic variations can influence pollinator behavior, particularly in environments characterized by high temperatures and intense evaporation, leading to reductions in the variability of nectar concentrations during the period of floral anthesis that can ensure a stable energy source for pollinators (Martínez‐Peralta & Martínez‐Zavala, 2021; Nicolson & Nepi, 2005). Under those circumstances, nectar becomes one of the main floral resources sustaining pollinators, constituting in some cases the only form of water available to floral visitors in times of scarcity (Petanidou et al, 2008).…”