Arrojadoa is a genus of cacti in the family Cactaceae (order Caryophyllales), comprising about 9 species endemic to northern Brazil. Described by Britton & Rose in 1920, the genus is named after the Brazilian botanist Miguel Arrojado Lisboa.
Species of Arrojadoa have slender, frail stalks that may be upright or procumbent, reaching up to 2 m in height and 2–5 cm in thickness. The stems typically bear 10–15 ribs, and branching is rare, usually occurring from the base. The snake-like growth habit makes them well suited to hanging baskets in cultivation, though they are considered difficult to grow.
Flowers are nocturnal and tubular, measuring 1–3 cm in length and 0.5–1 cm in diameter, with colours ranging from pink to carmine. The fruit is berry-like, spherical, up to 1.5 cm in diameter, and ripens to pink or red. Plants grow in rocky habitats under shrubs, which provide structural support for their fragile stems. They are subtropical and tolerate very little frost.
Notable species include Arrojadoa rhodantha, A. penicillata, A. dinae, and A. multiflora. Cultivation requires a slightly humid, well-draining soil with ample water during the growing season (spring to autumn) and a dry winter rest at a minimum temperature of 10 °C. Propagation is more successful from seed than from cuttings.
Etymology
The genus Arrojadoa was named by Nathaniel Lord Britton and Joseph Nelson Rose in 1920 in honour of Miguel Arrojado Lisboa (1872–1932), a Brazilian botanist who was superintendent of the Brazilian Railways at the time of the genus's description.
Distribution
Arrojadoa is endemic to northern Brazil, occurring in the states of Bahia, Minas Gerais, and Piauí. Plants grow in rocky places, typically under shrubs that provide structural support for their frail stalks. The genus is subtropical and has very little tolerance for frost.
Ecology
Arrojadoa species inhabit rocky outcrops and stony ground in subtropical northern Brazil, where they grow sheltered beneath shrubs. The shrubs protect the fragile cactus stems from direct exposure while allowing filtered light. The genus has minimal frost tolerance, consistent with its tropical to subtropical range.
Cultivation
Members of Arrojadoa are prized in cultivation for their snake-like, trailing growth habit, which makes them well suited to hanging baskets. However, they are considered challenging to grow. In good conditions they grow relatively quickly. A slightly humid, free-draining soil is recommended, with generous watering during the active growing season (spring through autumn). In winter, plants require a dry rest period and a minimum temperature of 10 °C. Propagation is more successful from seed than from stem cuttings.
Taxonomy
The genus was described by Britton & Rose in 1920 and is classified in the family Cactaceae, order Caryophyllales. As of 2025, Plants of the World Online accepted nine species. Several taxa formerly placed in Arrojadoa have been reclassified into other genera: A. bahiensis is now Pierrebraunia bahiensis, A. hofackeriana is now Micranthocereus hofackerianus, and A. leucostele is now Stephanocereus leucostele, among others. A newly described species, A. luetzelburgioides (N.P.Taylor & Zappi, 2024), was not yet formally accepted by POWO as of early 2026.
