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| The genera of Cactaceae |
The plants succulent; condensed-cactoid; low and very compacted in their entirety. The stems spiny to not spiny; small, more or less flattened- discoid to globose; apically depressed to not apically depressed; cephaliate (the cephalium cushion-like, comprising long bristles and woolly hairs). The plants unbranched; erect; usually solitary; to 0.02–0.09 m high. The stems not segmented; low- ribbed and grooved. The ribs 10–22; borne spirally, or longitudinal; rather broad-based. The plants conspicuously tuberculate (in that the ribs are notched into conical ‘warts’). The tubercles plump, prominent, closely opposed. The tubercles connected by the ribs; spirally disposed, or borne in longitudinal series. The areoles associated with tubercles; closely approximating. The components of adjacent areoles so extensively covering the mature plant body as to obscure any ribs or furrows, or not obscuring details of the plant body. The areoles spirally disposed, or borne in longitudinal series; simple (these small at the tubercle tips); woolly; with spines. The spines solitary to clustered (often obscuring the areoles); 4–11; 0.5–5 cm long; with radials and centrals differentiated (the radials being larger or smaller than the central one), or showing little or no difference between radials and centrals. Central spines 1. Radial spines 5–12. The spines stiff; straight, or curved, or straight and curved; terete. The mature stems leafless.
Flowering at night. The flowers aggregated; terminal (associated with the cephalia); one per areole; salver-shaped, the perianth limb broad; sessile; large; 5–10 cm long; fragrant; regular. The receptacle conspicuously produced beyond the ovary into a tubular hypanthium. The hypanthial tube exserted beyond the cephalium; not naked; with scales. The axils of the scales of the hypanthial tube more or less naked. The hypanthial tube spineless. The perianth sequentially intergrading from sepals to petals, or petaline, or of ‘tepals’; white. The perianth segments spreading (above the tube); elongate, relatively narrow; pointed. Stamens adnate to the perianth (inserted in the upper part of the tube).
The mature fruit 2.5–4.5 cm long; white, or pink, or red; globose to oblong or clavate, with persistent floral remains, slightly fleshy to non-fleshy when mature; dehiscent; dehiscing vertically by one slit, or dehiscing vertically by more than one slit ("via vertical slits"). The seeds 2–2.5 mm long; black; globose or sub-globose to ovoid; not encased in bony arils. The testa shiny; minutely papillate, or tuberculate. Cotyledons reduced or vestigial.
Natural Distribution. Brazil, eastern Bolivia, northern Paraguay.
Classification. 8 species. Subfamily Cactoideae. Tribe Trichocereeae.
Cf. Hunt, 1967.
Images. • Discocactus araneispinus (cf. D. zehntneri subsp. boomianus): © Zoya Akulova (2016). • Discocactus bahiensis, with Melocactus harlowii, M. lemairei (both as Cactus) and Melocactus violaceus (as Cactus): Britton & Rose (1922).
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa. See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2018 onwards. The genera of Cactaceae: descriptions, illustrations, identification, and information retrieval. Version: 14th November 2021. delta-intkey.com’.
