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Genus Arthrocereus in Family Cactaceae

In botanical taxonomy, a genus (plural genera) is a rank used to group closely related species within a family. In the hierarchy, genus sits below family and above species.

Genera are defined by shared morphological, anatomical, and genetic characteristics (for example, features of flowers, fruits, seeds, or leaves) that indicate a close evolutionary relationship among the species they contain.

Each genus can include one or more species. Examples include Rosa (roses) and Solanum (nightshades, including tomato and eggplant).

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Genus Description

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Arthrocereus (authority A. Berger) is a small columnar cactus in the family Cactaceae that includes about seven species (POWO, 2024; WFO, 2024). All taxa are endemic to the high‑altitude campos rupestres of southeastern Brazil, chiefly in Minas Gerais and adjacent states, where they occur on quartzite and sandstone outcrops between 800 and 2000 m. The genus was erected in 1905 (A. Berger) to accommodate several former Cereus species from Brazil. Plants are upright, often branching, with cylindrical stems 0.5–1.5 m tall bearing 5–9 ribs; areoles are woolly and armed with many spines of variable length. Leaves are absent, as in other cacti. Flowers are nocturnal, funnel‑shaped, 5–8 cm long, white to pink, with a long tube and numerous stamens; the ovary is inferior and the fruit is a small fleshy berry containing numerous black seeds. The centre of diversity lies in the Serra do Cabral–Serra da Mantiqueira region, where several narrow endemics are confined to rock outcrops; A. horripilus is known only from the Jequitinhonha Valley, while A. rondonianus is restricted to a few localities in São Paulo. Typical habitats are open, nutrient‑poor grasslands with abundant exposed rock, often subject to fire and seasonal drought. The base chromosome number is x = 11, consistent with most Cactaceae (Hunt et al., 2006). Traditional treatments have not recognized infrageneric groups, but recent molecular work places Arthrocereus within the tribe Trichocereeae as a monophyletic lineage (Nyffeler & Eggli, 2010). A phylogenomic study (Sánchez et al., 2022) recovered the genus nested within the broader Echinopsis clade and proposed synonymising it under that genus; however, major checklists (POWO, 2024; WFO, 2024) continue to treat Arthrocereus as distinct, reflecting ongoing taxonomic uncertainty. Species of Arthrocereus are occasionally cultivated by cactus enthusiasts for their compact, columnar habit and nocturnal blossoms, but none are of commercial horticultural importance. Within Brazil, a few specialty nurseries have introduced selected Arthrocereus taxa as ornamental columnar cacti for rock‑garden and xeriscape designs. Many taxa are listed as vulnerable or endangered because of habitat loss from mining, agriculture, and climate change, making targeted field surveys and ex situ conservation a priority. Continued phylogenetic resolution and updated Red List assessments will be essential for the genus’s future protection.

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