Rapicactus
| Rapicactus | |
|---|---|
| File:Rapicactus beguinii.jpg | |
| Kingdom | Plantae |
| Family | Cactaceae |
| Subfamily | Cactoideae |
| Tribe | Cacteae |
| SubTribe | |
| Genus | Rapicactus |
| Species | |
| Notes | |
Rapicactus is a genus of small geophytic cacti in the family Cactaceae, native to Mexico. It is characterized by a large napiform taproot and a reduced above-ground stem, often making the plant appear partially subterranean.
Etymology
The name Rapicactus means "turnip cactus", referring to the characteristic swollen taproot resembling a turnip.
Description
Rapicactus species are small, globose to short-cylindrical plants, often constricted at the base and typically solitary.
- Large napiform taproot, often exceeding the aerial portion
- Stem reduced, frequently partially buried
- Apex woolly
- Ribs absent; body divided into tubercles
- Areoles woolly, bearing dense, straight spines
Flowers are:
- Diurnal
- Funnel-shaped
- White to pink
- Produced at the apex
Fruits are berry-like, and seeds are striate with distinct hilum and micropyle.
Taxonomy
The genus Rapicactus was originally described by Franz Buxbaum and Oehme in 1942.
For many years, it was included within Turbinicarpus, but modern molecular phylogenetic studies have demonstrated that Turbinicarpus in a broad sense is polyphyletic.
Studies by Donati & Zanovello and Vázquez-Sánchez et al. support the recognition of Rapicactus as a distinct genus.
Species
Currently, 6 species and 1 subspecies are recognized:
- Rapicactus beguinii
- Rapicactus beguinii subsp. hintoniorum
- Rapicactus booleanus
- Rapicactus mandragora
- Rapicactus pailanus
- Rapicactus subterraneus
- Rapicactus zaragozae
Habitat
Species of Rapicactus inhabit extremely arid environments:
- Rocky limestone slopes
- Dry soils with minimal vegetation
- Sometimes acidic substrates
They are highly adapted and often mimic surrounding stones.
Altitude range:
- ~1000 – 3200 meters
Distribution
Endemic to Mexico:
- Coahuila
- Nuevo León
- San Luis Potosí
- Tamaulipas
- Zacatecas
Notes
Some taxonomic interpretations differ:
- Lüthy (2003): treats R. pailanus as a subspecies of R. mandragora
- Some classifications merge the genus into Turbinicarpus
- Modern consensus increasingly supports Rapicactus as a distinct lineage
References
- Buxbaum (1942)
- Hunt et al. – The New Cactus Lexicon (2006)
- Donati & Zanovello (2003–2005)
- Vázquez-Sánchez et al. (2013)
