Astrophytum
| Astrophytum | |
|---|---|
| File:Astrophytum myriostigma.jpg | |
| Kingdom | Plantae |
| Family | Cactaceae |
| Subfamily | Cactoideae |
| Tribe | Cacteae |
| SubTribe | |
| Genus | Astrophytum |
| Species | |
| Notes | Taxonomy follows Joël Lodé (2015). |
Etymology
The name Astrophytum means "Star plant", referring to the typical star-like shape of several species within the genus.
Description
Astrophytum is a genus of usually solitary and highly variable plants. Their forms range from flattened and globose to elongated or shortly columnar. A distinctive feature of most species is the presence of flaky white scales (trichomes) covering the epidermis, though some have spiny scales. The stems have well-defined ribs, except for A. caput-medusae, which possesses very elongated tubercles. Spines may be present or absent depending on the species.
The flowers are diurnal, self-sterile, and emerge apically. They are funnel-shaped and typically yellow, though some species feature a red or orange centre. Pollination is primarily carried out by bees. The fruits are globose, covered with persistent scales, and become dehiscent (split open) when ripe. The seeds are brown, light, and helmet-shaped. Seed dispersal occurs through hydrochory (water) or myrmecochory (ants).
The genus is divided into three sub-genera:
- Astrophytum: Species with yellow flowers and fruits with apical dehiscence (e.g., A. myriostigma, A. ornatum).
- Neoastrophytum: Species with bicoloured flowers (red/orange centre) and fruits with basal or irregular dehiscence (e.g., A. asterias, A. capricorne, A. coahuilense).
- Stigmatodactylus: Includes only the tuberculate species A. caput-medusae.
Habitat
Astrophytums grow in the Chihuahua Desert, the central plateau of Mexico, and the southern plains of Texas. They are found from 100 m (A. caput-medusae) up to 2000 m in altitude. Their habitat varies from rocky grounds and limestone mounds to clay alluvial soils and dry lake beds. They often grow in the shade of grasses and shrubs within the "matorral" vegetation, alongside other Cactaceae and Bromeliads.
Distribution
- Mexico (Coahuila, Durango, Guanajuato, Hidalgo, Nuevo León, Querétaro, San Luis Potosí, Tamaulipas, Zacatecas)
- USA (Texas)
Species
According to the Joël Lodé index, the genus includes the following 6 recognized species and 2 subspecies:
- Astrophytum asterias
- Astrophytum capricorne
- Astrophytum caput-medusae
- Astrophytum coahuilense
- Astrophytum myriostigma
- Astrophytum myriostigma subsp. potosinum
- Astrophytum myriostigma subsp. tulense
- Astrophytum ornatum
Notes
- Molecular studies (Vázquez-Sánchez et al., 2013) have confirmed that Astrophytum is a monophyletic genus.
- The species A. caput-medusae was originally described under the genus Digitostigma, but is now widely accepted within Astrophytum despite its atypical morphology.
- Phylogenetic data shows that Astrophytum is closely associated with Echinocactus, though notably excluding Echinocactus grusonii.
- The genus is highly popular in cultivation, leading to the creation of countless artificial hybrids and cultivars.
