Autor: Britton & Rose
• ETYMOLOGY
In Greek, ≪top cactus≫, referring to the characteristic top-shaped form of the plants in this genus.
• DESCRIPTION
A genus of plants usually solitary, sometimes branched, hemicryptophytic, sclerotic, globose, turbinate or cylindrical, the apex strongly depressed and woolly. Ribs absent, tubercles imbricated and spiralled, rhomboid flattened, keeled at the base; areoles woolly, garnished with 1-4 flexible spines emerging, deciduous over time.
Flowers diurnal, (self-sterile?), appearing at the apex, funnel-shaped, pale yellow or pink magenta, pollinated by bees. Fruits elongated, naked or scaly, somewhat fleshy, pale red magenta, with longitudinal dehiscences (only one in S. corregidorae), releasing freely the seeds. Seeds tiny, globose to almost pear-shaped, brown, with a large, whitish strophiola, absent in S. corregidorae. Seed dispersal ensured by ants.
• HABITAT
The genus Strombocactus grows in limited habitats but often in large numbers and as a mimetic plant, in canyons, on vertical cliffs, or very oblique faces, on arid limestone soils consisting of clastic sediments with fine particles (lutites), almost completely devoid of vegetation or in a xerophytic scrub (matorral), from 950 up to 2000 m in altitude.
• DISTRIBUTION
Mexico (Guanajuato, Hidalgo, Queretaro).
Currently 2 recognised species + one subspecies:
– Strombocactus corregidorae* Arias & Sanchez 2010
– Strombocactus disciformis* (DC.) Britton & Rose 1922
– Strombocactus disciformis subsp. esperanzae Glass & Arias 1996 (= S. pulchra)
References: "TAXONOMY of the CACTACEAE" - ISBN 978-84-617-3692-8 (Vol. 2)