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The families of flowering plants

L. Watson and M. J. Dallwitz

Cactaceae Juss.

Including Leuchtenbergiaceae Salm-Dyck ex Pfeiff., Nopalaceae (Nopaleaceae) Burnett, Opuntiaceae Martinov

Habit and leaf form. Mostly bizzare herbs, or shrubs; non-laticiferous (usually), or laticiferous (rarely). ‘Normal’ plants (more or less, in Pereskieae only), or switch-plants; nearly always ‘cactoid’, with succulent, photosynthetic stems (with highly modified short-shoots represented by ‘areoles’ which usually bear spines representing modified leaves, as well as hairs and/or bristles). Leaves well developed (Pereskieae), or much reduced to absent (mostly, persuasively interpretable as having (1), main stem leaves variously absent or vestigial, often reduced to their bases and represented by more or less conspicuous tubercles; and (2), leaves of the areolar short-shoots represented by spines). Plants succulent (mostly), or non-succulent (Pereskieae, with only ‘more or less fleshy’ leaves). Perennial. Self supporting, or epiphytic, or climbing (occasionally, e.g. Pereskia spp.); when climbing, scrambling. Pachycaul. Xerophytic. Leaves when present and identifiable as such, often caducous; of main stems, when present, usually minute to small, or medium-sized (Pereskieae); when present on main stems flat, or rolled, or terete; ‘herbaceous’, or fleshy, or membranous (usually small and ephemeral), or modified into spines (in the areoles); of main stems, when present, petiolate to sessile; simple. Lamina entire; when present on main stems, one-veined, or pinnately veined; cross-venulate, or without cross-venules. Leaves exstipulate.

General anatomy. Plants with laticifers (anastomosing, e.g. in Coryphantha, Leuchtenbergia, Neomamillaria), or without laticifers (usually).

Leaf anatomy. Minor leaf veins without phloem transfer cells (Opuntia, Zygocactus).

Axial (stem, wood) anatomy. Secretory cavities present, or absent; when present, with latex, or with mucilage (but mucilage cells much commoner). Cork cambium present; initially superficial. Nodes when recorded, unilacunar (with one trace, this often bi- or multi-fid). Primary vascular tissues principally comprising a ring of bundles (but sometimes exhibiting additional strands in the cortex and/or pith); collateral. Internal phloem absent. Cortical bundles present, or absent. Medullary bundles present, or absent. Secondary thickening usually ultimately developing from a conventional cambial ring (via an interfascicular cambium linking the main ring of bundles). Primary medullary rays wide. The axial xylem with vessels (usually), or without vessels.

The wood diffuse porous, or semi-ring porous to diffuse porous. The vessels very small (mostly), or medium to large (e.g., large in Pereskia); solitary, radially paired, in radial multiples, and clustered, or in tangential arcs (rarely). The vessel end-walls simple (typically), or reticulately perforated (rarely). The vessels without vestured pits; without spiral thickening. The axial xylem with tracheids, or without tracheids; without vasicentric tracheids; without fibre tracheids; with libriform fibres; at least sometimes including septate fibres, or without septate fibres. The fibres without spiral thickening. The parenchyma typically paratracheal. ‘Included’ phloem absent.

Reproductive type, pollination. Plants hermaphrodite (usually). Pollination anemophilous, or entomophilous, or ornithophilous, or cheiropterophilous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; terminal or lateral; when aggregated, in cymes. The ultimate inflorescence units cymose. Flowers medium-sized to large (often showy); fragrant (often), or odourless; regular to somewhat irregular; when irregular, zygomorphic. The floral irregularity (when noticeable) involving the perianth, or involving the perianth and involving the androecium. Flowers partially acyclic. The perianth acyclic, or the perianth acyclic and the androecium acyclic. Free hypanthium present, or absent.

Perianth sequentially intergrading from sepals to petals, or petaline; 20–100 (‘many’); basally joined, or free; spotted; green and white, or cream, or yellow, or orange, or red, or pink, or purple.

Androecium 15–100 (‘many’). Androecial members branched, or unbranched; maturing centrifugally; free of the perianth (occasionally), or adnate (to the perianth tube); free of one another, or coherent (sometimes in groups). Androecium exclusively of fertile stamens. Stamens 15–100 (‘many’). Anthers dehiscing via longitudinal slits; introrse; bilocular; tetrasporangiate. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. Anther wall initially with one middle layer. Tapetum glandular. Pollen grains aperturate; 3 aperturate, or 6–15 aperturate; colpate, or foraminate, or rugate; spinulose; 3-celled (recorded in 8 genera).

Gynoecium 3–100 carpelled (to ‘many’). The pistil 1 celled (nearly always), or 2–15 celled (?—Pereskia). Gynoecium syncarpous; synstylovarious; inferior (nearly always), or superior (Pereskia). Ovary 1 locular (but occasionally partially partitioned). Locules partially secondarily divided by ‘false septa’ (Pereskia), or without ‘false septa’ (usually). Epigynous disk present (within the hypanthium). Gynoecium stylate. Styles 1; apical. Stigmas 3–100 (as many as G); wet type; non-papillate; Group IV type. Placentation parietal (usually), or basal (Pereskia). Ovules in the single cavity 15–100 (‘many’); long funicled; arillate, or non-arillate; circinotropous, campylotropous (usually), or anatropous; bitegmic; crassinucellate. Outer integument not contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked (sometimes with filiform apparatus). Endosperm formation nuclear.

Fruit fleshy (usually), or non-fleshy; indehiscent (usually), or dehiscent (rarely); a capsule (rarely), or a berry (usually). Seeds non-endospermic. Perisperm present, or absent. Seeds winged, or wingless. Seeds with starch. Embryo rudimentary at the time of seed release to well differentiated. Cotyledons 2 (when differentiated, free or united). Embryo achlorophyllous (in all 5 species from the 4 genera sampled); straight, or curved (usually), or other than straight, curved, bent or coiled (sometimes spiral).

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. CAM (nearly always), or C3 (very rarely). C3 physiology recorded directly in Pereskia, in the leaves only. CAM recorded directly in Bergerocactus, Carnegiea, Cereus, Cephalocereus, Chamaecereus, Copiapoa, Coryphantha, Echinocactus, Echinocereus, Echinopsis, Eulychnia, Ferocactus, Lobivia, Lophocereus, Machaerocereus, Mammillaria, Melocactus, Myrtillocactus, Neochilena, Neolloydia, Nopalea, Notocactus, Opuntia, Pachycereus, Phyllocactus, Pilocopiapoa, Rhipsalis, Trichocereus, Zygocactus (etc.? — ‘all genera’, according to Smith and Winter, 1996). Cyanogenic (rarely), or not cyanogenic. Alkaloids present (usually), or absent. Iridoids not detected. Betalains present. Saponins/sapogenins present, or absent. Proanthocyanidins absent. Flavonols present, or absent; quercetin, or kaempferol and quercetin. Ellagic acid absent (3 genera). Sieve-tube plastids P-type; type III (a).

Geography, cytology. Temperate, sub-tropical, and tropical. Chiefly in the drier regions of tropical America, but reaching Patagonia and ascending to the High Andes; only Rhipsalis (perhaps introduced) in Africa, Madagascar, Mauritius, Seychelles and Ceylon. X = 11. Supposed basic chromosome number of family: 11.


Species about 2000. Genera about 90 (according to Gunn et al. 1992, other estimates varying from 50 to 150); Acanthocalycium, Acanthocereus, Aporocactus, Ariocarpus, Armatocereus, Arrojadoa, Arthrocereus, Astrophytum, Austrocactus, Aztekium, Bergerocactus, Blossfeldia, Brachycereus, Brasilicereus, Browningia, Calymmanthium, Carnegiea, Cephalocereus, Cereus, Cipocereus, Cleistocactus, Coleocephalocereus, Copiapoa, Corryocactus, Coryphantha, Denmoza, Discocactus, Disocactus, Echinocactus, Echinocereus, Echinopsis, Epiphyllum, Epithelantha, Eriosyce, Escobaria, Espostoa, Espostoopsis, Eulychnia, Facheiroa, Ferocactus, Frailea, Gymnocalycium, Haageocereus, Harrisia, Hatiora, Heliocereus, Hylocereus, Jasminocereus, Leocereus, Lepismium, Leptocereus, Leuchtenbergia, Lophophora, Maihuenia, Mammillaria, Melocactus, Micranthocereus, Mila, Myrtillocactus, Neolloydia, Neoporteria, Neoraimondia, Neowerdomannia, Obregonia, Opuntia, Oreocereus, Pachycereus, Parodia, Pediocactus, Pelecyphora, Peniocereus, Pereskia (stems), Pereskiopsis, Pilosocereus, Pseudorhipsalis, Pterocactus, Rebutia, Rhipsalis, Samaipaticereus, Schlumbergera, Sclerocactus, Selenicereus, Stenocactus, Stenocereus, Stephanocereus, Stetsonia, Strombocactus, Tacinga, Thelocactus, Uebelmannia, Weberbauerocereus, Weberocereus, Zygocactus.

Economic uses, etc. The most popular plant family with collectors of succulen plants, with numerous genera and species offered in dealers’ lists and represented in collections. Some edible fruits (prickly pear, India fig, tuna, arridari, pitaya).

Illustrations. • Technical details: Opuntia, Cactus. • Habit and technical details: Rhipsalis, Epiphyllum, Pereskia. • Aporocactus flagelliformis: Bot. Mag. 17 (1786). • Chamaecereus silvestrii: L.W., photo. • cf. Echinocereus leucanthus: as Cereus leucanthus, Bot. Reg. xxvi, 13 (1840). • Echinopsis eyriesii: as Echinocactus, Bot. Reg. 1707, 1835. • cf. Heleocereus speciosus: as Cereus speciosissimus, Bot. Reg. 49, 1842. • Malacocarpus ottonis: as Echinocactus, Bot. Reg. XXIV, 42 (1838). • Malacocarpus scopa: Bot. Reg. 1839, 24. • Mammillaria pulchra: Bot. Reg. 1329, 1830. • Opuntia vulgaris: as O. monacantha, Bot. Reg. 1726, 1835. • Pereskia aculeata: Bot. Reg. 1928, 1837. • Pereskia grandifolia: as Pereskia bleo, Bot. Reg. 1473 (1831). • Habit: Echinocactus, Rhipsalis.

