Cactaceae subfam. Cactoideae
Bot. Dict. ed. 4, 43. 1836.
Trees, shrubs, or short perennial plants, solitary to forming mats, columnlike or barrel-shaped to spheric stem succulents, sometimes geophytic or epiphytic, erect to prostrate, scrambling, climbing, or hanging, freely branched or unbranched. Roots diffuse, taproots, or tuberlike, sometimes adventitous. Stems segmented or unsegmented, usually conspicuously succulent with thick cortex and pith, surface usually ribbed or tuberculate, usually somewhat woody with wood confined to internal ring, bark sometimes becoming proximally hardened and woodlike; areoles circular to linear [protracted into finger-shaped shoots in Neoraimondia of South America], hourglass-shaped in some genera, with spiny portion separated from flowering portion by a groove in the stem surface, spiny areoles completely separate from flowering areoles in some genera, bearing 0–90 spines, glochids absent. Spines acicular, subulate, daggerlike, ribbonlike, hairlike, or bristlelike, smooth, rough, striate, or annulate-ridged, glabrous (rarely pubescent), epidermis intact, not separating as sheath. Leaves absent or rudimentary and microscopic or nearly so, less than 1 mm. Flowers diurnal to nocturnal, bisexual (rarely unisexual or functionally so), solitary in areoles (rarely several), radially symmetric (rarely bilateral), sessile, broadly salverform, urceolate, funnelform, or long tubular; flower tube epigynous, usually conspicuous, adnate to upward extension of stem surrounding ovary, 0.2–15[–30] cm; triangular leaflike bracts or small scales sometimes present on ovary and flower tube; nectary often apparent, forming open chamber surrounding base of style. Fruits dehiscent or indehiscent, depressed-spheric or spheric to long clavate, juicy, fleshy, or dry; perianth persistent or deciduous. Seeds 1–3000+, yellowish, reddish, brown, or black, spheric, comma-shaped, lenticular-reniform, pyriform, or obovoid, 0.4–5 mm, rarely strophiolate, never arillate.
Almost throughout New World from southern Canada to s South America, Rhipsalis disjunct to Africa, Madagascar, and Sri Lanka, some species in horticulture almost worldwide.
Genera ca. 111, species ca. 1500 (28 genera, 121 species in the flora).
Subfamily Cactoideae is the most diverse group of the Cactaceae, in terms of size, architecture, habitat, and habit. The vast majority of North American species are xerophytic, with columnar to spheric or barrel-shaped stems. A few are geophytic, that is, stems are mostly deep-seated in the soil substrate, often with the plant consisting mostly of an enlarged taproot and the visible parts of the stems appearing nearly flush with the soil surface or nearly buried during drought, becoming taller and slightly more conspicuous only during the growing season. Fewer species still, are epiphytic, and those only in the tropical and subtropical regions of North America and South America.
In the following treatments, most authors have attempted to recognize varieties wherever current evidence is compelling. Where evidence is equivocal, our tendency has been to include greater variability within varieties and, hence, fewer formal trinomials. Unfortunately, in the absence of strong supporting evidence, herbarium specimens of cacti are usually inadequate for the purpose of making taxonomic decisions. As a consequence, some populations of conservation interest here have been placed into synonmy before critical studies have been conducted to determine quantitatively and objectively how distinct each population is, or which deserve varietal status. Authors do not intend to imply that other varieties should not eventually be recognized. More systematic work, including DNA research and field research of all variants, is needed as a prelude to reassessing the status of currently listed and proposed populations. Such populations need to be protected during the entire phase of analysis and reassessment.