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bishop's-cap (Astrophytum myriostigma)

Astrophytum myriostigma is a succulent cactus that is usually solitary and grows upright, with the stem changing from globose toward a columnar or short-columnar form. It is reported to be perennial.

LightIt takes full sun to bright partial sun and needs ample light in cultivation, although sources differ and intense direct sun in hot summer conditions may cause sunburn.
WaterWater moderately during the growing season after the growing medium has dried, reduce watering as temperatures fall, and keep it dry during winter dormancy while avoiding standing water and prolonged wetness. A winter wa
HumidityIt is reported to need moderate airflow.
TemperatureSources differ on the minimum temperature, with limited information placing it at about -6 °C. It is generally reported to tolerate brief light frost. It rests cool and dry in winter. A single source gives a cold minimum
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Overview

Astrophytum myriostigma is a succulent cactus that is usually solitary and grows upright, with the stem changing from globose toward a columnar or short-columnar form. It is reported to be perennial.

Origin and habitat

Sources differ on the precise native range, describing highlands from northeastern to north-central Mexico and specifically mentioning Coahuila, Durango, Nuevo León, San Luis Potosí, and Tamaulipas. Sources differ in their habitat descriptions, which include desert or dry scrub with stony, limestone-rich soils on scrubby alluvial plains, foothills, and steep slopes. It is native to dry Mexican desert, scrub, and highland environments and is adapted to dry, fast-draining habitats.

Characteristics

Sources differ, but mature plants are reported at about 60–100 cm tall and about 10–20 cm wide. It is reported to grow slowly. Sources differ in their descriptions of the flowers and flowering period; flowers appear near the stem apex, are yellow to pale yellow and often funnel-shaped, with some having orange to red coloring at the center or base, while flowering in the wild is mainly in early spring and cultivated plants may flower in summer or the warm season. Sources differ on the fruit, describing it as green to red, oblong to rounded, sometimes splitting open in a star-like pattern when mature, with some accounts describing red fruit with a hairy surface.

Light

It takes full sun to bright partial sun and needs ample light in cultivation, although sources differ and intense direct sun in hot summer conditions may cause sunburn.

Watering

Water moderately during the growing season after the growing medium has dried, reduce watering as temperatures fall, and keep it dry during winter dormancy while avoiding standing water and prolonged wetness. A winter watering interval of 30–60 is specified.

Humidity and airflow

It is reported to need moderate airflow.

Temperature and dormancy

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

Growing medium and mounting

Sources differ somewhat, but the growing medium is described as well-drained, airy, relatively nutrient-poor, and neutral to slightly alkaline; limestone material may be included, and its natural habitat commonly has stony, limestone-rich soils. It needs a fast-draining mix. A specialist source reports that it is not epiphytic.

Feeding

Fertilizing in spring and summer is reported to promote growth.

Propagation

Propagation is mainly by seed, with sowing in early spring; some horticultural forms are also grafted to speed growth. Cuttings are also listed as a propagation method.

Common problems

Mealybugs and root mealybugs may affect the plant. It is generally reported to have few disease problems. Overly wet growing medium in cold conditions can readily lead to rot, while intense summer light can cause sunburn. It can withstand brief cold conditions, but wetness should be avoided at low temperatures, and strong summer light may cause sunburn.

Identification

Sources differ in some details, but Astrophytum myriostigma is spineless, has prominent longitudinal ribs that may increase with age, and has a star-shaped cross-section. Its epidermis is usually densely covered with fine white hair-like scales or tufts that give it a gray-white appearance, although some horticultural forms lack this white covering.

Photos

Astrophytum myriostigma
📷 Dav Hir · CC BY-SA 3.0 · source
Astrophytum myriostigma
📷 sergio niebla from Cd. Victoria, Tamaulipas, México · CC BY-SA 2.0 · source

Sources