Opuntia Mill.

Scientific Description

Common name. Prickly Pear. Family Cactaceae.

Habit and leaf form. ‘Arborescent’, or shrubs; when present and identifiable as such, deciduous (often caducous); non-laticiferous and without coloured juice. Switch-plants (spiny, with clusters of spines in hairy areoles); with the principal photosynthesizing function transferred to stems and ‘cactoid’ (phyllocladinous, the stems segmented with flattened segments). Leaves much reduced (scale-like). Plants succulent. Leaves cauline. Young stems oval in section (or cylindroidal). Stem internodes solid (stem jointed, basal segments form trunk). Self supporting. Pachycaul. Xerophytic. Leaves alternate (scattered, ‘indeterminate’); spiral; with blades (scale-like, often spinose), or bladeless; membranous and modified into spines; sessile (more or less); non-sheathing; simple. Leaf blades entire; solid (or conical); terete; conical. Leaves without stipules. Leaf anatomy. Hairs present, or absent (areoles with woolly, jointed hairs, short bristles, glochids and spines; the rest of phyllocladodes glabrous). Extra-floral nectaries absent (nectary ring on inner surface of hypanthium). Stem anatomy. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous, or ornithophilous.

Inflorescence and flower features. Flowers solitary; sessile; ebracteate; medium-sized to large (showy); fragrant; regular to somewhat irregular; slightly zygomorphic. The floral asymmetry 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; bears modified leaves; short and obovoid, truncate or depressed at apex; short floral tube is fused to hypanthium apex and shed after flowering. Perianth sequentially intergrading from sepals to petals; 20–100 (many); joined (basally); yellow. Calyx polysepalous, or gamosepalous. Corolla if perianth so interpreted, 20–100 (‘many’); yellow. Androecial members indefinite in number. Androecium 100. Androecial members branched, or unbranched; maturing centrifugally; adnate (to the floral tube); free of one another, or coherent. Androecium exclusively of fertile stamens. Stamens 20–100 (many); all more or less similar in shape; arranged spirally on hypanthium apex. Anthers dehiscing via longitudinal slits; introrse; bilocular; tetrasporangiate. Gynoecium 3–100 carpelled (to ‘many’). The pistil 1 celled. Gynoecium syncarpous; synstylovarious; inferior. Ovary unilocular; 1 locular. Epigynous disk present (within the hypanthium). Gynoecium stylate. Styles 1; apical. Stigmas 5–10. Placentation parietal. Ovules in the single cavity 20–50 (numerous); long funicled; circinotropous, campylotropous, or anatropous.

Fruit and seed features. Fruit fleshy; indehiscent; a berry; 1 celled; 20–100 seeded. Seeds non-endospermic. Perisperm present, or absent. Seeds winged, or wingless. Embryo rudimentary at the time of seed release to well differentiated. Cotyledons 2 (when differentiated). Embryo straight, or curved.

Economic uses, etc. Edible fruits (prickly pear).

Etymology. From the Latin Opuntius; of or belonging to Opus, a town in Greece.