Grusonia
| Grusonia | |
|---|---|
| File:Grusonia bradtiana.jpg | |
| Kingdom | Plantae |
| Family | Cactaceae |
| Subfamily | Opuntioideae |
| Tribe | Cylindropuntieae |
| SubTribe | |
| Genus | Grusonia |
| Species | |
| Notes | Taxonomy follows Joël Lodé (2015). Lodé treats Grusonia in a restricted sense, excluding Corynopuntia and Micropuntia. |
Etymology
The genus is named in honor of Hermann August Gruson (1821–1895), a German industrialist, inventor, and succulent collector who owned one of the largest cactus collections in Europe at the time.
Description
Grusonia consists of shrubby cacti that form dense, low-growing thickets or mats.
- Stems: Cylindrical segments (joints) that are distinctly ribbed, a feature that distinguishes them from most other Opuntioids.
- Areoles: Small, containing white wool, glochids (tiny barbed bristles), and spines.
- Spines: Strong, needle-like, and covered with a papery sheath (tunic) when young, similar to Cylindropuntia.
- Flowers: Diurnal and self-sterile, appearing at the tips of the stems. They are typically yellow or greenish-yellow.
- Fruits: Globose to urceolate (urn-shaped), fleshy at first but becoming dry, often bearing spines and glochids.
- Seeds: Large, pale yellow to brownish, and characterized by a hard, bony aril (seed coat).
Habitat
The genus grows in extremely arid desert regions, often on limestone slopes, gravelly plains, or volcanic soils. They are found at altitudes between 500 m and 1500 m.
Distribution
- Mexico: Coahuila, Chihuahua, Durango, Zacatecas.
- USA: Limited populations in Texas and New Mexico (near the border).
Species
Following the restricted circumscription of Lodé (2015), the genus is reduced to only 3 recognized species:
- Grusonia bradtiana (Type species)
- Grusonia pulchella (Note: Often moved to Micropuntia by others, but Lodé keeps it here tentatively)
- Grusonia rochensis
Taxonomy
The circumscription of Grusonia has been subject to significant debate. While the "New Cactus Lexicon" merged Corynopuntia and Marenopuntia into Grusonia, Lodé maintains their separation based on distinct morphological differences in stem structure (ribbed vs. tuberculate) and seed characters. Molecular studies (Wallace & Dickie, 2002) support the distinctiveness of these lineages within the tribe Cylindropuntieae.
