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sanddollar (Astrophytum asterias)

Astrophytum asterias is a small, solitary, spineless perennial cactus with a flattened globular to disc-like, globular growth form.

LightAstrophytum asterias takes full sun, and cultivation information indicates that ample sunlight supports continued flowering.
WaterIt requires little water; watering can be somewhat greater during the growing season than in winter, but the medium should dry between waterings, remain very dry in winter, and not become waterlogged.
HumidityIt is reported to prefer low humidity.
TemperatureA single source reports a lower temperature around -6 °C; it also describes the plant as tolerating brief light frost and as frost hardy. It is generally reported to have an upper temperature limit and a USDA hardiness-z
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Overview

Astrophytum asterias is a small, solitary, spineless perennial cactus with a flattened globular to disc-like, globular growth form.

Origin and habitat

It is native to southern Texas in the United States around the lower Rio Grande, and to Tamaulipas and Nuevo León in northeastern Mexico; its remaining wild distribution is greatly reduced, and the Nuevo León population may be regionally extinct. It occurs in dry thorn scrub, grassland, and rocky or gravelly places, including hills, depressions, and beside dry riverbeds, on substrates that include gravelly alluvial loam and saline or calcareous clay. Plants are often shaded by other vegetation or rocks and may be largely buried in soil and sand. Its habitat has a warm-temperate to subtropical, semi-desert, dry or semi-arid climate.

Characteristics

Sources differ on mature size, giving a height of about 2.5–6 cm and a spread of about 5–15 cm. It is reported to grow slowly. Flowers are borne at the top of the plant and are yellow with red at the base or throat; the exterior may be conspicuously hairy. Sources differ in their descriptions of flowering time, while the fruit is described differently as well; it is oval, green to pink, and covered with soft hairs.

Light

Astrophytum asterias takes full sun, and cultivation information indicates that ample sunlight supports continued flowering.

Watering

It requires little water; watering can be somewhat greater during the growing season than in winter, but the medium should dry between waterings, remain very dry in winter, and not become waterlogged.

Humidity and airflow

It is reported to prefer low humidity.

Temperature and dormancy

A single source reports a lower temperature around -6 °C; it also describes the plant as tolerating brief light frost and as frost hardy. It is generally reported to have an upper temperature limit and a USDA hardiness-zone classification. It rests cool and dry in winter.

Growing medium and mounting

Sources differ, but the growing medium is described as alkaline, porous, and well drained.

Feeding

A single source reports that half-strength liquid fertilizer can be used after flower buds form.

Propagation

Propagation is mainly by seed, which can germinate quickly; some cultivated varieties are also propagated by grafting or vegetatively.

Common problems

Root rot is reported as a disease problem. Wild populations are threatened mainly by habitat destruction and excessive illegal collection; urban development, agriculture, road construction, herbicides, and scrub removal are also listed as causes of decline. It prefers dry conditions and should remain dry in cool periods.

Identification

Sources differ in their descriptions, but the plant is flattened-globular and spineless, usually with low ribs arranged in a star pattern; the ribs bear large white woolly areoles, while the epidermis often has white scaly flecks, producing a regular star-like appearance from above.

Photos

Astrophytum asterias
📷 GaleoC · CC BY-SA 3.0 · source
Astrophytum asterias
📷 Devon Bradley, some rights reserved (CC BY), uploaded by Dev · CC BY · source

Sources