Vivipary and offspring survival in the epiphytic cactus Epiphyllum phyllanthus (Cactaceae)

Abstract

Vivipary, the germination of seeds before they are shed from the parent plant, is a rare event in angiosperms involving complex ecophysiological processes. Pseudovivipary and cryptovivipary occur in approximately 30 (2%) species of the cactus family. A remarkable case of vivipary in Epiphyllum phyllanthus is described here. Information is provided regarding the biology of viviparous fruits, morphology, mortality, survival rates of viviparous offspring, and some eco-evolutionary implications of this reproductive strategy in the Cactaceae. This epiphytic cactus has no host-specific relationship. A low proportion (33.3%) of individuals produced viviparous fruits. Seed number/fruit varied from 197 to 230 with percentage of viviparous germination from 97.5% to 99%. The viviparous seedlings exhibited normal development and were no different from non-viviparous offspring. Transplanting experiments showed that the first week is critical for seedling establishment, and high mortality occurred in the three treatments used: 69% on the phorophyte surface, 58.6% on the ground, and 44.8% under controlled conditions. The number of survivors gradually stabilized, and the contribution to establishment was comparable in each of the treatments after the acclimation phase. It is suggested that vivipary is associated with thermoregulation, parental care, conspecific nursing, and rapid seedling establishment. Germination is not a limiting factor in the perpetuation of this viviparous species, but seedling establishment is. In viviparous individuals of E. phyllanthus, seedling mortality during establishment rather than failure to germinate within the fruit is a limiting factor affecting local population density. Overall, viviparity is an intrinsic, genetic event involving high metabolic costs favouring germination and dispersal of the fittest offspring regardless of substrate and environmental conditions.