37a. Cactaceae Jussieu subfam. Pereskioideae Engelmann in W. H. Brewer et al., Bot. California. 1: 243. 1876 (as Peirescieae).
Michael W. Hawkes
Trees, shrubs, or woody climbers, erect or scrambling, usually freely branching, not cactuslike, resembling other woody plants. Roots diffuse or tuberlike. Stems unsegmented, not ribbed or tuberculate, not especially succulent, becoming woody with age; areoles in leaf axils, circular, bearing 1 to several spines, glochids absent. Spines persistent, usually acicular, straight, less often curving and catclaw-like, smooth, glabrous, epidermis intact, not separating as sheath. Leaves deciduous, alternate, often petiolate [subsessile]; blade broad, flat, fleshy or ± succulent, resembling leaves of other broad-leaved plants. Flowers diurnal, bisexual [or unisexual], in axillary or terminal racemes, corymbs, panicles, or cymose panicles of 1-70+ flowers [solitary or fasciculate], radially symmetric, stalked [subsessile to sessile], ± rotate [broadly campanulate-urceolate]; tepals perigynous or epigynous, flower tube not apparent; ovary subtended by broad leaflike scaly bracts; nectar chamber not apparent. Fruits indehiscent, spheric, pyriform, or broadly depressed-obovate, fleshy; perianth and contained flower parts ± persistent. Seeds 2-150+, black, lenticular to obovate or subreniform, 1.7-7.5 mm, not strophiolate or arillate.
Genus 1, species 17 (2 species in the flora): introduced; tropical and subtropical regions in the New World from central Mexico and the West Indies southward to northern Argentina.
The monogeneric Pereskioideae is the smallest North American subfamily of Cactaceae. Recently, subfam. Maihuenioideae P. Fearn, of South America, was segregated on the basis of DNA and morphologic data. It has long been generally accepted that the cactus family had its origin in a Pereskia-like ancestor, because species of Pereskia, with their broad leaves, woody, barely succulent habits, and relatively primitive-looking flowers, more closely resemble typical, leafy dicotyledonous plants than succulent cacti (A. C. Gibson and P. S. Nobel 1986; B. E. Leuenberger 1986). In addition, species of Pereskia are reported to have the C3 photosynthetic pathway, unlike stem-succulent cacti, which have crassulacean acid metabolism (A. C. Gibson and P. S. Nobel 1986). Recent analyses of DNA data confirm that Pereskia have DNA sequences that are primitive for the family (R. S. Wallace and A. C. Gibson 2002).