Homalocephala
| Homalocephala | |
|---|---|
| File:Homalocephala texensis.jpg | |
| Kingdom | Plantae |
| Family | Cactaceae |
| Subfamily | Cactoideae |
| Tribe | Cacteae |
| SubTribe | |
| Genus | Homalocephala |
| Species | |
| Notes | Taxonomy follows Joël Lodé (2015). Lodé resurrects this genus for the former Echinocactus texensis based on molecular data showing it is closer to Ferocactus than to Echinocactus s.s. |
Etymology
The name is derived from the Greek homalos (even/level) and kephale (head), referring to the characteristic flattened, disk-like appearance of the plant's apex.
Description
Homalocephala is a monotypic genus consisting of a very robust, low-growing, and slow-growing cactus.
- Stems: Solitary, globose to strongly flattened (discoid), often partially buried in the soil. It can reach up to 30 cm in diameter but rarely exceeds 15-20 cm in height. The epidermis is thick, leathery, and dark green.
- Ribs: Numerous (typically 13 to 27), prominent, and acute.
- Spines: Extremely strong, thick, and annulated (ringed). The central spine is particularly large, flattened, and downward-pointing. These spines are famous for being able to puncture heavy leather and even horse hooves.
- Flowers: Diurnal and self-sterile, appearing from the woolly center of the apex. They are funnel-shaped, fragrant, and have elegantly fringed petals. Colors range from pale pink to white, consistently featuring a deep magenta or reddish throat.
- Fruits: Globose, fleshy, and brilliant red when ripe. They are covered in white wool and thin scales, eventually drying out.
- Seeds: Relatively large (for the tribe), black, and smooth.
Habitat
The genus grows in a wide variety of environments, including dry grasslands, prairies, and rocky limestone hills in the Chihuahuan Desert. It is remarkably hardy, capable of withstanding both extreme drought and significant frost.
Distribution
- USA: Southeastern New Mexico, southwestern Oklahoma, and throughout most of Texas.
- Mexico: Chihuahua, Coahuila, Durango, Nuevo León, San Luis Potosí, Tamaulipas, and Zacatecas.
Species
Following the classification of Lodé (2015), the genus is monotypic:
- Homalocephala texensis (Type species)
Taxonomy
Traditionally classified as Echinocactus texensis, recent molecular phylogenetic studies (Vázquez-Sánchez et al., 2013) have demonstrated that this species is not closely related to the "true" Echinocactus (like E. platyacanthus). Instead, it represents a distinct and ancient lineage within the North American Cacteae, more closely related to the Ferocactus and Leuchtenbergia clade. Lodé maintains it as a separate genus to reflect this evolutionary distance.
