| | The genera of Cactaceae |
Including Cactus Britton & Rose
The plants cerioid to condensed-cactoid; low and very compacted in their entirety, or low and very compacted in their entirety to not ‘low and very compacted’. The stems spiny; discoid to shortly cylindric; apically depressed, or not apically depressed; cephaliate (very conspicuously so, cephalia comprising long woolly hairs and bristles or spines developed from the apical areoles). The plants erect; solitary; to 0.06–1 m high. The stems not segmented; ribbed and grooved. The ribs 8–27; longitudinal. The grooves wide. The plants not conspicuously tuberculate, or conspicuously tuberculate to not conspicuously tuberculate. The tubercles if interpreted as such, represented by notches in the ribs. The tubercles connected by the ribs; borne in longitudinal series. The areoles not tubercle-associated, or associated with tubercles to not tubercle-associated (depending on interpretation); distant. The components of adjacent areoles so extensively covering the mature plant body as to obscure any ribs or furrows (occasionally), or not obscuring details of the plant body (usually). The areoles borne in longitudinal series; simple (small to large). The flowering areoles differing in form from the non-flowering ones (in the woolly and bristly cephalia). The areoles with bristles, or without bristles; very with spines. The spines clustered; 3–30 (to 21 or more"); 0.1–8 cm long; showing little or no difference between radials and centrals; never hooked; straight, or curved. The mature stems leafless.
Flowering short lived, during the day. Pollination entomophilous (?), or ornithophilous (primarily hummingbirds). The flowers terminal; one per areole; salver-shaped, the perianth limb broad (the expanded limb comprising few petals); sessile; small; 1.5–6 cm long; regular. The receptacle conspicuously produced beyond the ovary into a tubular hypanthium to scarcely produced beyond the ovary (?); naked. The hypanthial tube short, immersed in the cephalium; naked; without scales; spineless. The perianth sequentially intergrading from sepals to petals, or petaline, or of ‘tepals’; white (to pinkish), or pink. Stamens adnate to the perianth (inserted in the upper part of the tube).
The mature fruit 1–2.8 cm long; clavate; white, or red; naked; exserted from the cephalium when mature, fleshy; indehiscent (?). The seeds with a truncate hilum, black; globose or sub-globose to ovoid; not encased in bony arils; with hilum and micropyle conjunct. The testa shiny; more or less verrucose. Cotyledons reduced or vestigial.
Natural Distribution. Western Mexico through central America south to Ecuador and southern Peru, east through the Amazon to eastern Brazil and Venezuela, and into the Caribbean.
Classification. About 35 species. Subfamily Cactoideae. Tribe Cereeae.
Cf. Hunt (1967).
Images. • Melocactus conoideus: © Zoya Akulova (2014). • Melocactus conoideus: © Zoya Akulova (2014). • Melocactus conoideus: © Zoya Akulova (2014). • Melocactus harlowii, M. lemairei (both as Cactus) and Melocactus violaceus (as Cactus melacactoides), with Discocactus bahiensis: 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’.
