Vivipary in the Cactaceae: Its taxonomic occurrence and biological significance

Vivipary, a rare reproductive strategy in flowering plants, has been previously reported in only four species of the Cactaceae. In this paper, eight additional examples (Cleistocactus smaragdiflorus, Disocactus martianus, the hybrid Epiphyllum X Fern la Borde, Harrisia martinii, Lepismium ianthothele, L. monacanthum, Rhipsalis micrantha forma micrantha, and R. baccifera subsp. horrida) of vivipary in cultivated cacti from tribes Hylocereeae, Rhipsalideae, and Trichocereeae are documented. The plants had fully-developed and mature fruits containing seeds at different stages of germination, including tiny embryos emerging from the seed coat to young, healthy seedlings with well-developed organs, such as cotyledons and radicles. Several features, though not unique, distinguish cactus fruits with viviparous seedlings. Foremost, the fruits are fleshy with abundant mucilage and a relatively thick, often transparent pericarp. The seeds are generally numerous and embedded in a transparent, white or red pulp. The occurrence of vivipary in taxa from four phylogenetically distinct tribes of the subfamily Cactoideae suggests an independent origin and indicates that this reproductive strategy may be more widespread in the family than originally thought. Vivipary in the Cactaceae is regarded as a form of cryptovivipary, a condition in which the zygote develops inside the fruit without penetrating the ovary wall for dispersal purposes, which in turn is considered a subcategory of true vivipary. Further, vivipary is interpreted as an adaptive reproductive strategy that enables seedlings to establish more rapidly.