Rapicactus
| Rapicactus | |
|---|---|
| File:Rapicactus beguinii.jpg | |
| Kingdom | Plantae |
| Family | Cactaceae |
| Subfamily | Cactoideae |
| Tribe | Cacteae |
| SubTribe | |
| Genus | Rapicactus |
| Species | |
| Notes | Taxonomy follows Joël Lodé (2015). The genus is accepted as distinct from Turbinicarpus. |
Etymology
The name means "turnip cactus", referring to the large napiform taproot characteristic of this genus.
Description
Rapicactus is a genus of small geophytic cacti highly adapted to arid environments.
- Habit: Globose to short cylindrical plants, usually solitary, often partially subterranean, with woolly apex.
- Roots: Large napiform taproot, often exceeding the size of the aerial stem.
- Stems: Without ribs, divided into tubercles, often constricted at the base.
- Spines: Dense, straight, sharp, arising from woolly areoles.
- Flowers: Diurnal, funnel-shaped; white to pink; self-sterile; appearing at the apex.
- Fruits: Berry-like.
- Seeds: Striate, with distinct hilum and micropyle.
Habitat
The genus inhabits extremely arid and specialized environments, often where few other cacti can survive.
- Rocky limestone slopes and cliffs
- Dry, mineral soils
- Occasionally acidic substrates
Altitude range: from about 1000 m up to 3200 m.
Plants are often cryptic and mimic surrounding stones.
Distribution
- Mexico:
Coahuila, Nuevo León, San Luis Potosí, Tamaulipas, Zacatecas
Taxonomy
The genus Rapicactus was established by Buxbaum & Oehme (1942).
It has long been included within Turbinicarpus, but morphological and molecular studies (Donati & Zanovello; Vázquez-Sánchez et al.) demonstrate that Turbinicarpus in a broad sense is polyphyletic.
These studies support the resurrection of Rapicactus as a distinct genus.
According to Joël Lodé (2015), Rapicactus is a valid genus.
Species
Following the classification of Joël Lodé (2015).
- Rapicactus beguinii
- Rapicactus booleanus
- Rapicactus mandragora
- Rapicactus pailanus
- Rapicactus subterraneus
- Rapicactus zaragozae
Notes
- The genus is highly specialized for survival in extreme arid habitats.
- Its large taproot allows water storage and drought resistance.
- Previously treated within Turbinicarpus, but now widely accepted as distinct.
