Cactaceae
Acanthocalycium
Acanthocalycium
Genus of cacti endemic to Argentina with four accepted species. The globular to short-cylindrical, very spiny stems produce tubular flowers with scales and spines on the floral tube — a character giving the genus its name ("spiny calyx," from Greek akanthos + kalyx). They inhabit arid and semi-arid zones of the Andean provinces of central-northwestern Argentina, especially on rocky slopes and ravines between 500 and 2,500 m.
Acanthocereus
Acanthocereus
Genus of cacti with columnar or scrambling stems and well-defined angular ribs (3–5 ribs), long spines, large white nocturnal flowers, and edible red fruits. Widely distributed across tropical America, from southern Florida to northern South America, in tropical coastal habitats, dry scrublands, and riverbanks.
Acharagma
Acharagma
Genus of small globular cacti endemic to northeastern Mexico, with two accepted species. Related to Escobaria and Mammillaria, they are distinguished by unique floral and seed characters: seeds with a well-developed aril and flowers emerging from the apex. They inhabit arid limestone slopes of the Chihuahuan Desert and the mountain ranges of northeastern Mexico.
Ancistrocactus
Ancistrocactus
Small globular cacti from southern Texas and northeastern Mexico, with conical tubercles and strongly hooked central spines — hence the name, from the Greek ankistron (hook). They inhabit xerophytic scrublands on calcareous or clay soils, often in areas of seasonal rainfall. A small genus, with only two widely recognized species, both with restricted distribution and under pressure from illegal collection and habitat loss.
Ariocarpus
Ariocarpus
Genus of living rock cacti endemic to Mexico and the extreme southern tip of Texas, with 6–7 accepted species. Their flattened or hemispherical bodies, with triangular or leaf-like tubercles and no spines in maturity, mimic rock and soil, making them extraordinarily cryptic in their habitat. Lifespan of centuries, extremely slow growth, and high vulnerability to collection. All species are protected under CITES Appendix I.
Armatocereus
Armatocereus
Genus of columnar or arborescent cacti with segmented stems and marked spiny ribs, native to the Pacific Andean slopes. Their annual segments are clearly distinguishable on mature stems, giving them an unmistakable articulated appearance. White to pinkish flowers, nocturnal or crepuscular. They produce edible fleshy fruits known as pitajayas in local communities. They inhabit zones from arid coastal areas to mountain slopes of the western Andean cordillera in Ecuador, Peru, and Colombia.
Arrojadoa
Arrojadoa
Genus of slender, bamboo-like columnar cacti from the semi-arid caatinga of northeastern Brazil, with 5–6 accepted species. Their stems produce at the end of each growing season a pseudocephalium — an annular crown of spines and woolly hairs — from which the tubular flowers in red to deep pink emerge. They inhabit the caatinga and rupestrian fields of northeastern Brazil. Named in honor of Brazilian engineer and botanist Miguel Arrojado Ribeiro Lisboa (1872–1932).
Arthrocereus
Arthrocereus
Genus of slender and articulated columnar cacti endemic to the rupestrian grasslands and quartzitic outcrops of the state of Minas Gerais, Brazil, with 3–4 accepted species. Their thin, very spiny stems produce white to pinkish flowers that open at night, often fragrant, with a very long style. Related to Disocactus and the epiphytic clade, but terrestrial. They inhabit crevices of quartzitic rocks at elevations of 900–2,000 m.
Astrophytum
Astrophytum
Genus of globular to short-cylindrical cacti from northern Mexico and the extreme southern tip of Texas, with 4–5 accepted species. They are distinguished by their spineless bodies in the most well-known species (though some have spines), covered in small white stellate scales or hairs giving them a silvery or mottled appearance. Yellow flowers with red or orange center, diurnal and large relative to the plant body. Highly prized in cactus collections for their perfect geometric form and their long history of breeding in Japan, where hundreds of cultivars have been created.
Austrocactus
Austrocactus
Genus of small globular to ovoid-cylindrical cacti from southern Patagonia and the southern Andes, with 4 accepted species. They are the southernmost cacti in the world, capable of withstanding hard frosts and snowfall. Their central spines are frequently hooked at the tip. They inhabit arid Patagonian steppes and Andean slopes from Mendoza to southern Patagonia in Argentina, and in Chile from Atacama to Coquimbo.
Austrocylindropuntia
Austrocylindropuntia
Genus of cylindrical opuntias from the Andes and Pacific coasts of South America, with some 10–12 accepted species. Distinguished from Opuntia by their clearly cylindrical (not flattened) stems and persistent rudimentary leaves. They occupy an extraordinarily wide altitudinal range, from the arid Pacific coasts to the high-Andean summits (4,500 m), including the singular high-Andean opuntias covered in woolly hairs (A. floccosa) and coral-like opuntias with flattened segments (A. clavarioides). Widely used as living fences and as a source of fruits in the Andes.
Aztekium
Aztekium
Genus of three extremely slow-growing cacti endemic to the gypsum cliffs of Nuevo León, Mexico. Their bodies have ribs with additional transverse folds that resemble the bas-reliefs of Aztec architecture, from which the genus name derives. They are the slowest-growing known cacti (millimeters per year), which, combined with habitat destruction and illegal collection, makes them extremely vulnerable. All three species are protected under CITES Appendix I.
Bergerocactus
Bergerocactus
Monotypic genus of colonial coastal cacti, native to the coastal strip of California (USA) and Baja California (Mexico). Its bright green cylindrical stems, densely covered in golden-yellow spines, grow prostrate or semi-erect on rocky coastal slopes with marine influence. The genus was established in honor of German naturalist Alwin Berger. Its only species, B. emoryi, is one of the few plants that grow on the rocky coastal cliffs of southern California.
Blossfeldia
Blossfeldia
Monotypic genus housing the world's smallest cactus, B. liliputana, whose adult body can measure just 1 cm in diameter. It lacks ribs and has flat, tiny spiral tubercles. During extreme drought it almost completely dehydrates and contracts until visually integrated with the rock, reanimating with rain (poikilohydry). Inhabits crevices of calcareous or granitic rocks in northwestern Argentina and Bolivia. Named in honor of German collector Harry Blossfeld.
Brachycereus
Brachycereus
Monotypic genus of small columnar cacti endemic to the Galápagos Islands. Its single species, the lava cactus, colonizes recent lava flows and arid coastal zones where few plants survive, frequently being the first colonizer on bare volcanic substrates.
Brasilicereus
Brasilicereus
Genus of columnar cacti from eastern Brazil, with slender stems and nocturnal tubular flowers. They grow in caatinga, cerrado and rupicolous vegetation on rocky outcrops, tolerating extended dry periods.
Brasiliopuntia
Brasiliopuntia
Genus of arborescent cacti related to Opuntia, endemic to South America. It is characterized by a main cylindrical woody trunk from which flattened cladode branches arise, creating an unusual tree-like silhouette within the subfamily Opuntioideae.
Browningia
Browningia
Genus of columnar cacti in the family Cactaceae native to the western Andes of Peru and Bolivia. Produces branched columns of imposing appearance with numerous ribs and robust spines. Its nocturnal flowers, white or pink, are large. Genus named in honour of W.E. Browning. Inhabits ravines and dry Andean valleys at moderate altitudes.
Calymmanthium
Calymmanthium
Small genus of columnar cacti from northern Peru, notable for its unusual floral structure that distinguishes it from other genera: its flowers are partially covered by bracts forming a kind of sheath or cover (hence the name, from Greek "kalymma", cover). It grows in dry inter-Andean valleys at mid-elevations.
Carnegiea
Carnegiea
Monotypic genus containing the saguaro, the largest columnar cactus in North America and an iconic symbol of the Sonoran Desert. Its imposing columns with upward-curved arms can reach 15 m in height and live more than 150 years. The genus was named in honour of philanthropist Andrew Carnegie.