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sanddollar (Astrophytum asterias)

Astrophytum asterias is a small, perennial succulent cactus, usually solitary, with a strongly flattened globular to disc-shaped stem that grows close to the ground and is typically unbranched and spineless.

LightAstrophytum asterias takes full sun, and ample sunlight helps support flowering.
WaterIt needs little water; the growing medium should dry between waterings, with somewhat more water during summer growth and dry conditions in cold weather and winter, while avoiding standing water to reduce the risk of roo
HumidityIt is generally reported to prefer low humidity.
TemperatureSources differ on the lower temperature limit, with the limited evidence placing it at about -6 °C. It is generally reported to tolerate brief light frost and to be frost hardy. It rests cool and dry in winter. A single
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Overview

Astrophytum asterias is a small, perennial succulent cactus, usually solitary, with a strongly flattened globular to disc-shaped stem that grows close to the ground and is typically unbranched and spineless.

Origin and habitat

The wild species is native to southern Texas around the lower Rio Grande and to Tamaulipas and Nuevo León in northeastern Mexico; its wild distribution has greatly contracted, and the Nuevo León population may be regionally extinct, while “Super Kabuto” is a horticultural cultivar. It occurs in dry thorn scrub, grassland, hills, depressions, and around dry riverbeds, on gravelly alluvial loam, saline or calcareous clay, and rocky ground; plants often grow close to or partly embedded in the ground and may be shaded by other plants or rocks. Its habitat ranges from warm-temperate to subtropical semi-desert, dry, or semi-arid environments with relatively low annual rainfall.

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 emerge from the top of the plant and are yellow with a red to orange-red base or throat, with conspicuous hairs on the exterior; flowering occurs mainly from late spring through summer. The fruit is reported to be oval, green to pink, and covered with hairs.

Light

Astrophytum asterias takes full sun, and ample sunlight helps support flowering.

Watering

It needs little water; the growing medium should dry between waterings, with somewhat more water during summer growth and dry conditions in cold weather and winter, while avoiding standing water to reduce the risk of root rot. Winter watering is given at intervals of 30–60 days.

Humidity and airflow

It is generally reported to prefer low humidity.

Temperature and dormancy

Sources differ on the lower temperature limit, with the limited evidence placing it at about -6 °C. It is generally reported to tolerate brief light frost and to be frost hardy. It rests cool and dry in winter. A single source gives a cold minimum of about -6 °C.

Growing medium and mounting

It needs a porous, fast-draining cactus mix; sources differ on pH, with one preferring an alkaline medium and genus-level information recommending an acidic, sandy medium.

Feeding

It is reported that half-strength liquid fertilizer can be applied after flower buds form.

Propagation

Astrophytum asterias can be propagated from seed, with seeds reported to germinate relatively quickly, and some cultivars are also grafted. For “Super Kabuto,” sources differ on the principal propagation method: one describes clonal propagation, while another says it is usually propagated from seed.

Common problems

Overly wet or waterlogged growing medium creates a risk of root rot. Wild populations are threatened mainly by habitat destruction and overcollection, with urban development, agricultural use, and road construction also listed as factors in their decline. The species is adapted to dry environments, while sources differ on its cold tolerance.

Identification

“Super Kabuto” is a horticultural cultivar of Astrophytum asterias distinguished by especially large, dense, fluffy white spots or hair-like scales that can form conspicuous dense patterns; spot size and density can vary markedly among individuals.

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