Genus scope and historical names
The Plants of the World Online treatment adopted in the atlas includes 27 species of Sclerocactus, occurring in the southwestern and south-central USA and northern Mexico. The broad genus circumscription includes taxa formerly separated as, among others, Ancistrocactus, Echinomastus and Toumeya. These names appear in older monographs and on collectors’ labels. [2-WWW]
Changes also concern species boundaries. Sclerocactus dawsoniae, described in 2024, includes the northern portion of populations formerly assigned to S. glaucus in Colorado. In the same decade, S. tobuschii received a species-level combination in Sclerocactus. In the publication on its response to fire from 2021, it appears as S. brevihamatus subsp. tobuschii. When interpreting results, the name and geographical provenance of the plants studied jointly determine their present-day placement. [McGlaughlin and Naibauer 2023] [Reemts and Ferrato 2021] [2-WWW]
A small stem in different habitats
In the species discussed, stems are nearly globular, flattened or shortly cylindrical. Their surfaces are divided into ribs or distinct tubercles with areoles that produce radial and central spines. In S. wrightiae, one central spine has a hooked tip. In S. papyracanthus, the long, flattened spines resemble dry grass leaves. These details have greater diagnostic value than small plant size alone. [Ortiz-Brunel et al. 2023] [Heil and Porter 2003b]
Habitats differ in soil properties and surrounding vegetation. S. mesae-verdae inhabits heavy, clayey substrates with little vegetation cover. The Mexican site of S. papyracanthus lies in a saline grassland community. S. tobuschii occupies shallow soils over limestone in a mosaic of grasslands and woody vegetation. A mineral site can therefore mean either swelling clay or a stony crevice with little soil depth. [Coles et al. 2012] [Ortiz-Brunel et al. 2023] [Reemts and Ferrato 2021]
Reproduction and life beneath the surface
Seed formation depends on pollen transfer between flowers. In the populations studied, S. wrightiae showed self-incompatibility, rejection of its own pollen by the reproductive system. S. mesae-verdae was partly self-compatible. In both species, fruit set required pollinators. [Tepedino et al. 2023]
Seeds of S. wrightiae can survive in soil at least until the next season. Their density in the population studied was greatest near adult plants. This persistent seed bank separates dispersal and seedling emergence in time. The outcome then depends on seed viability, germination conditions and survival of the youngest plant. [Lariviere et al. 2024]
Recruitment rate and regeneration
Long-term observations of S. mesae-verdae show two pathways for rebuilding the aboveground portion of the population. Seedlings reached a size allowing flowering after 7–11 years. Shoots regrowing on damaged plants could flower in the first year, and usually within three years. Flowering can therefore return much faster after damage than a new individual from seed can mature. [Coles et al. 2012]
Detailed monitoring distinguishes plants, their stems and seedlings. It also includes individuals temporarily difficult to see, flowering status and traces of damage. During attempts to photograph S. wrightiae by drone, even the lowest flight tested revealed only some of the plants found on the ground. Changes in visible cactus numbers can therefore result from both biological processes and detection conditions. [Bates et al. 2022] [Coles et al. 2012]
Related articles
Synonyms and names in the literature
Ancistrocactus · Coloradoa · Echinomastus · Papyrocactus · Roseia · Toumeya [2-WWW]