Grusonia is a genus of opuntioid cacti in the family Cactaceae, order Caryophyllales, native to the arid and semi-arid deserts of the southwestern United States and northern Mexico. The genus encompasses what were formerly treated as two separate genera — Grusonia and Corynopuntia (the "club chollas") — merged following a 2016 molecular phylogenetic study of the tribe Cylindropuntieae that demonstrated both groups were polyphyletic when kept apart. This circumscription has been accepted by Plants of the World Online since June 2021.
Plants in this genus grow in low cushion-like mounds made up of ovoid to slightly club-shaped stem segments, typically 1 to 25 centimetres long. The segments are tuberculate (bearing raised wart-like projections) rather than ribbed. Spines are stout and formidably barbed, covered along their margins with fine denticles and tipped with an epidermal sheath. Flowers are typically yellow; a few species produce pink to deep magenta blooms. The fruit is narrowly obconic to ellipsoid, initially fleshy but drying quickly, often malodorous and densely armed with glochids.
Club chollas are closely similar in appearance across species, which historically made the group difficult to study and led to many species going undescribed. Recent research has clarified species boundaries and revealed that, despite growing sympatrically, wild club chollas rarely hybridize naturally. The genus contains approximately 15 species recognised by GBIF, distributed across desert flats and gentle slopes from sea level to around 2000 metres elevation.
Etymology
The common name "club cholla" and the former genus name Corynopuntia both trace to the Greek coryne, meaning "club," a reference to the distinctively club-shaped stem segments. In Mexico the plants are colloquially called perritos ("little dogs"), likely alluding to the way the barbed spines cling like a nipping dog. Grusonia itself honours the German cactus collector and patron Hermann von der Gruson (1821–1895), after whom the famous Gruson Cactus Greenhouse in Magdeburg is also named.
Distribution
Grusonia occurs across the North American desert regions, ranging from California, Arizona, Nevada, New Mexico, and Texas in the United States south through the Mexican states of Baja California, Baja California Sur, Sonora, Chihuahua, Coahuila, Nuevo León, Durango, Zacatecas, San Luis Potosí, and Tamaulipas. Populations are found from near sea level to about 2000 metres elevation, inhabiting desert flats, bajadas, and gentle slopes throughout the Chihuahuan, Sonoran, and Mojave Desert systems.
Ecology
Club chollas grow in very dry, sun-exposed habitats on sandy, loamy, or gravelly soils. Several species have evolved a highly effective passive dispersal strategy: their tubercles detach with minimal contact, and the finely barbed spines catch on animal fur, feathers, or skin, carrying stem segments considerable distances before they drop and take root. This mechanism makes some species significant hazards for livestock and wildlife, as the embedded spines are difficult to remove and can cause lasting injury.
Taxonomy Notes
Grusonia has had a complex nomenclatural history. Corynopuntia was first erected in 1935 by Knuth as a segregate from Opuntia, then reduced to sectional rank by Benson in 1969, elevated to subgenus by Bravo in 1972, and included within an expanded Grusonia by Anderson in 1999. Molecular work by Dickie (1997), Wallace & Dickie (2002), Griffith (2003), and seed micromorphology by Stuppy (2002) supported reinstatement of Corynopuntia as a distinct genus, accepted by the Cactaceae Consensus Group in 2006. A comprehensive 2016 molecular phylogenetic study of tribe Cylindropuntieae overturned this again, showing both genera were polyphyletic in isolation; the combined Grusonia is now the accepted treatment on Plants of the World Online (from June 2021).
