Name and identification
Astrophytum myriostigma Lem. is an accepted species described in 1839. Its name refers to the many pale dots on the stem. The Polish collectors' name, bishop's cap, describes its star-shaped outline. The adopted classification includes subspecies myriostigma and quadricostatum. [2-WWW] [2-WWW] [2-WWW] [Szychowski b.d.b]
Stem, roots and development
Young plants are usually globose or shortly cylindrical. With age, some populations form broad, low columns, while other plants become distinctly slender. In the 2021 comparison, nominate subspecies plants reached about 52 cm tall, and plants treated by the authors as tulense up to about 90 cm. These values describe the groups considered, without setting a limit for the whole species. [Montanucci and Kleszewski 2021]
Five ribs are common, but rib number changes during growth and differs among individuals. Adults usually lack spines. Seedlings develop small, dark juvenile spines. White hair clusters may cover the stem densely, sparsely or be nearly absent. This continuous variation matters in understanding nudum. [Montanucci and Kleszewski 2019] [Montanucci and Kleszewski 2020] [Montanucci and Kleszewski 2021]
Flowers, fruits and seeds
Flowers open during the day and are yellow to pale yellow. In the 2021 comparisons, the nominate subspecies usually had more tepal rows than tulense plants. Flower size and structure depend on population. Older descriptions assigning every myriostigma a red throat require checking plant identification and possible hybrid origin. [Montanucci and Kleszewski 2019] [Montanucci and Kleszewski 2021] [Montanucci 2024]
Fruits are usually green, partly dry as they ripen and open from the apex. Seed size differs among populations. In the 2021 study, nominate subspecies seeds were larger on average than tulense seeds. A statistical difference in a sample does not provide a simple key for identifying every individual seed. [Montanucci and Kleszewski 2021]
Range and habitat
The species occurs in northeastern Mexico. Literature describes populations in San Luis Potosí, Tamaulipas and Nuevo León in detail. They occupy various elevations and microhabitats, usually associated with mineral substrates and rocky terrain. In the 2016 study, mean elevation of 119 records was 1354.7 m above sea level, with a standard error of 22.7 m. The older statement of occurrence around 2500 m should not be extended to the entire species. [2-WWW] [Carrillo-Angeles et al. 2016] [Montanucci and Kleszewski 2019] [Montanucci and Kleszewski 2020] [Montanucci and Kleszewski 2021]
Plants from densely hairy to almost bare were studied near Huizache. The proportion of bare individuals changed with location and elevation, but did not form a simple, exclusive elevation belt. In some observations, exposed bare plants lost their green colour while sheltered individuals retained it better. This relationship matters in acclimating nudum forms. [Montanucci and Kleszewski 2020]
Cultivation in Poland
The species can be grown on its own roots in a bright, airy location. Increase sunlight gradually after overwintering and relocation. Forms with few hairs need close observation of the stem surface. Healthy new tissue is a better guide than the colour of the old body alone. [Szychowski b.d.c] [Montanucci and Kleszewski 2020]
The substrate should be stable and permeable. The archived account cited Wery's mixture of 10% clayey sand and 30% each basalt gravel, pumice and crushed brick. The source does not explain whether percentages are by volume or mass, or give full particle sizes. The recipe is retained as a grower's historical experience. [Szychowski b.d.c]
Watering is linked to active growth and drying of the mixture. Mature plants can have a dry winter rest in cool, above-freezing temperatures. Archived material gives both a general 6–10°C and about 10°C in species profiles. Data are insufficient to regard either value as a universal threshold. [Szychowski b.d.c] [Anonim b.d.e]
Seeds propagate populations and cultivated lines. Cultivars may produce variable offspring, so record parents and assess seedling features through further growth. Some offsetting forms are maintained vegetatively. Grafting can accelerate development but changes plant proportions and makes requirements dependent on the rootstock. [Szychowski b.d.a] [Szychowski b.d.c] [12-WWW] [11-WWW]
Variation and similar species
The most common mistakes involve A. coahuilense and equating rib number with subspecies. Features distinguishing A. coahuilense include fruits opening at the base, a frequently coloured throat and seedling characteristics. Bare myriostigma plants fall within species variation. Geographical identification requires provenance data. [Montanucci 2008] [Montanucci and Kleszewski 2019] [Montanucci and Kleszewski 2020] [Montanucci and Kleszewski 2021] [Montanucci 2024]