| | The genera of Cactaceae |
The plants succulent; dwarf cerioid (often with a thick woody root); not ‘low and very compacted’. The stems spiny; slender elongate cylindric; 1.5–6 cm in diameter; neither cephaliate nor pseudocephaliate. The plants terrestrial and self supporting, or scrambling; branched, or unbranched; prostrate to erect; shrubby. The stems not columnar. The branches ellipsoid or cylindrical; low. The stems segmented; ribbed and grooved. The ribs 10–18; longitudinal. The grooves wide to deep and narrow. The plants not conspicuously tuberculate. The areoles not tubercle-associated; borne in longitudinal series (along the ribs); small, simple; without glochids; with spines. The spines many, clustered; 20–50; 0.5–7 cm long; with radials and centrals differentiated, or showing little or no difference between radials and centrals. Central spines when detectable, 1–2, or 6–8. Radial spines 18–50. The spines awl-shaped, stout or thin. The mature stems leafless.
Flowering at night. The flowers solitary; terminal to lateral (mostly on the sides of the terminal segments); one per areole; very elongate tubular; sessile; large; 6–8 cm long; regular. The receptacle conspicuously produced beyond the ovary into a tubular hypanthium. The pericarpel bearing a few acute scales and areoles sparsely to densely woolly with hairlike spines. The hypanthial tube with wool, hairlike spines and a few pointed scales; not naked; with scales; with spines. The perianth pale pink, or white. The perianth segments elongate, widely spreading; elongate, relatively narrow to relatively short, broad; pointed to acuminate. Stamens numerous; adnate to the perianth (variously inserted in the throat and tube); not exserted; sometimes in groups (with the uppermost displaced and forming a separate ring), or not grouped.
The mature fruit 2–3 cm long; globose, or clavate ("inverted pear-shaped"); green; not naked; spiny (with hairlike spines), or without spines; with persistent floral remains; globose to obovoid or clavate, with persistent floral remains, with scales and hairlike spines, somewhat fleshy; indehiscent. The seeds black; obliquely ovoid; curved, or not curved (?); not encased in bony arils. The testa dull; verrucose (with low warts and wavy depressions). Cotyledons reduced or vestigial.
Natural Distribution. Western and southeastern Brazil.
Classification. 5 species. Subfamily Cactoideae. Tribe Trichocereeae.
Cf. Hunt, 1967.
Images. • Arthrocereus rondonianus: © Daiv Freeman.
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’.
