Phenology of Pilosocereus leucocephalus (Cactaceae, tribe Cereeae): a columnar cactus with asynchronous pulsed flowering

Abstract

Pilosocereus leucocephalus produces flowers in discrete pulses, suggesting this cactus might exhibit pulsed flowering-a rare flowering pattern among angiosperms. In this study, we (1) describe the phenology of P. leucocephalus, (2) explore the influence of temperature, rainfall, and plant size on the flowering pattern, and (3) assess the effect of flowering phenology on the reproductive success of this cactus. Flowering phenology was characterized using the coefficient of variation in addition to traditional descriptors of flowering phenology: flowering onset, flowering duration, number of pulses and flowers, as well as flowering synchrony. The association between temperature, rainfall, plant size, and reproductive success (fruit set) with phenological descriptors was assessed using mixed-effects models. The flowering phenology of P. leucocephalus was confirmed as pulsed but was unexpectedly asynchronous. This cactus flowers during the warmest part of the year. We found a significant relationship between temperature and flower production. Plant size has a strong effect on all the flowering phenology descriptors we studied, except flowering synchrony. Of the phenological descriptors evaluated, only flowering onset has a significant and positive relationship with fruit set. These results strongly suggest that flowering phenology in P. leucocephalus (1) is mainly controlled by temperature and plant size and (2) influences its reproductive success.

Reproductive phenology of the Caribbean cactus Harrisia portoricensis: rainfall and temperature associations

“…The results of previous studies in columnar cacti have suggested that reproductive activity is mainly controlled by variations in one primary factor, either temperature or rainfall (Bowers 1996;Ruíz et al 2000;Petit 2001;Bustamante and Búrquez 2008;Munguías-Rosas and Sosa 2010). That was not the case for H. portoricensis, which exhibited very shortterm increments in bud production in response to proportional increments in mean and minimum temperatures and where subsequent rainfall events appear to be an environmental cue necessary to break the dormancy of buds and induce flowering.…”

“…Studies performed with different cactus species have demonstrated that the timing and intensity of the reproductive phenological patterns are principally affected not only by variation in rainfall (i.e., the start of the rainy season and total annual precipitation) but also by temperature variation (i.e., annual mean minimum and spring mean maximum temperatures) (Bowers 1996;Pavón and Briones 2001;Petit 2001;Bustamante and Búrquez 2008). In the case of columnar cacti, the relative influence of rainfall and temperature on phenology is not uniform across the species that have been studied, and their effects on reproductive timing can be positive, negative, or even nil (Bowers 1996;Ruíz et al 2000;Petit 2001;Bustamante and Búrquez 2008;Munguías-Rosas and Sosa 2010). For example, reproductive onset (triggering budding and flowering phenologies) and reproductive output of Cargenia gigantea in the northern Sonoran Desert (Arizona, USA) show a positive association with winter rainfall intensity (Bowers 1996).…”

Patterns of frugivory in the columnar cactusPilosocereusleucocephalus

“…Some basics of the role of animals in its frugivory networks are unknown (Munguía-Rosas & Sosa, 2010), and the first few questions of importance in understanding these relationships include: Which species of animals are frugivores of P. leucocephalus? What is the relative importance of each guild/species in removing its fruit pulp?…”

“…This Mesoamerican species, as well as many others in all four clades of columnar cacti, has received little attention from researchers in spite of its keystone position in tropical dry ecosystems. Some basics of the role of animals in its frugivory networks are unknown (Munguía‐Rosas & Sosa, ), and the first few questions of importance in understanding these relationships include: Which species of animals are frugivores of P. leucocephalus ? What is the relative importance of each guild/species in removing its fruit pulp?…”

Estructura poblacional de dos especies de cactáceas columnares en un bosque tropical caducifolio

“…En algunos bosques tropicales caducifolios y trópicos secos los cactus columnares son especies muy conspicuas, aunque han sido poco estudiadas (Bullock 2000, Delgado-Fernández et al 2017, Munguía-Rosas & Sosa 2010, Vázquez-Castillo et al 2019, y aún se desconoce sobre su dinámica poblacional y el tipo de reclutamiento en ambientes más húmedos que se caracterizan por tener temporada de lluvia totalmente predecible. Por ejemplo, en la estación biológica de Chamela la precipitación promedio anual es de 731 mm (Ayala 2016) y en la selva baja caducifolia del centro del estado de Veracruz hay registros de 750 mm promedio anual (Trejo-Vázquez 1999).…”