Astrophytum

Astrophytum
File:Astrophytum myriostigma.jpg
Kingdom	Plantae
Family	Cactaceae
Subfamily	Cactoideae
Tribe	Cacteae
SubTribe
Genus	Astrophytum
Species
Notes	Taxonomy follows Joël Lodé (2015) with molecular support from Cota & Wallace (1996), Bárcenas et al. (2011), Hernández-Hernández et al. (2011), and Vázquez-Sánchez et al. (2013).

Etymology

The name Astrophytum means “star plant”, referring to the star-shaped form of several species.

Description

Astrophytum is a genus of usually solitary cacti with distinctive ribbed or tuberculate bodies and characteristic epidermal trichomes.

• Habit: Solitary; rarely clustering; globose, flattened or short columnar.
• Roots: Thickened, adapted to arid conditions.
• Stems: Green to grey-green, often densely covered with white flaky scales (trichomes).
• Ribs: Well defined (typically 3–8), or replaced by elongated tubercles in some species.
• Tubercles: Present only in A. caput-medusae, elongated and irregular.
• Areoles: Small, often woolly; sometimes bearing spines.
• Spines: Present or absent depending on species.
• Flowers: Diurnal, apical, funnel-shaped; yellow, often with red or orange centre; self-sterile.
• Pollination: By bees.
• Fruits: Globose, scaly; dehiscent at maturity.
• Seeds: Brown, helmet-shaped; relatively light.
• Dispersal: By water (hydrochory) or ants (myrmecochory).

Habitat

Occurs in arid to semi-arid environments:

• desert scrub (matorral)
• rocky slopes and limestone outcrops
• gravelly and clay alluvial soils
• dry lake beds and ravines

Often growing among grasses and shrubs, sometimes partially shaded.

Altitude range: approximately 100–2000 m.

Distribution

North America:

• Mexico: Coahuila, Nuevo León, San Luis Potosí, Tamaulipas
• United States: Texas

Taxonomy

The genus is well supported as monophyletic.

Key points:

• Described by Lemaire (1839)
• Closely related to Echinocactus (excluding E. grusonii)
• Cota & Wallace (1996): phylogenetic proximity to Echinocactus
• Bárcenas et al. (2011): confirmed monophyly
• Hernández-Hernández et al. (2011): supported a distinct clade
• Vázquez-Sánchez et al. (2013): confirmed inclusion of A. caput-medusae

The previously proposed genus Digitostigma is included within Astrophytum.

Species

According to Joël Lodé (2015):

• Astrophytum asterias
• Astrophytum capricorne
• Astrophytum caput-medusae
• Astrophytum coahuilense
• Astrophytum myriostigma
  • Astrophytum myriostigma subsp. potosinum
  • Astrophytum myriostigma subsp. tulense
• Astrophytum ornatum

Notes

• One of the most recognizable cactus genera due to its star-shaped morphology.
• Highly variable, with numerous described forms, varieties and hybrids.
• Astrophytum caput-medusae represents an extreme morphological deviation within the genus.
• Adapted to environments with irregular rainfall and high temperature fluctuations.