Kroenleinia
Kroenleinia is a monotypic genus of cactus, created relatively recently to hold a single, instantly recognisable species: the beloved golden barrel cactus, Kroenleinia grusonii. Long placed in the large and now much-divided genus Echinocactus, the golden barrel was split out on the strength of its distinctive floral and seed characters, and today stands alone in its own genus.
Description
As a monotypic genus, Kroenleinia is defined by the traits of its one species. Plants form a large, solitary (occasionally clustering with age), globe-shaped body that flattens somewhat on top as it matures. The ribs are numerous, prominent and sharply defined, running vertically down the plant and lined with closely spaced areoles bearing stiff, golden-yellow spines. A dense crown of yellowish wool sits at the apex, from which the flowers emerge.
The features that separate Kroenleinia from the true Echinocactus species are chiefly technical: differences in the structure of the flowers and, in particular, the form and surface of the seeds. The bell-shaped yellow flowers ring the woolly crown in summer on mature plants, though flowering typically only begins once a plant has reached considerable size and age.
Distribution
The golden barrel is endemic to a restricted area of east-central Mexico, chiefly in the states of Querétaro and Hidalgo, where it grows on volcanic slopes and rocky outcrops. Despite being one of the most widely cultivated cacti on Earth, it is genuinely rare and threatened in the wild, its natural range fragmented by habitat loss (including the flooding of a major population behind a dam). Like all cacti it is listed under CITES, and wild collection is strictly prohibited; nursery-grown plants, however, are abundant and entirely legal to own and trade.
Notable species
Being monotypic, the genus contains just one accepted species:
- Kroenleinia grusonii — the golden barrel cactus, mother-in-law's cushion, or golden ball. This is the plant behind the entire genus.
Older references and plant labels will often still list this plant under its former name, Echinocactus grusonii. Both names refer to the same cactus.
Cultivation
Kroenleinia is famously easy-going and forgiving, which is a large part of why it became a nursery staple worldwide. Grow it in a very free-draining, mostly mineral mix and give it as much sun as you can — the more light, the denser and more golden the spination. Water generously through the warm growing season once the soil has dried, then keep the plant dry and cool through winter, when it needs a proper rest to stay healthy and to flower in later years.
The species is slow but steady, and can eventually reach the size of a beach ball or larger with decades of good care. Young plants make excellent, near-indestructible beginners' cacti. See Watering and Repotting for general technique, and handle with care — the golden spines are stiff and sharp.
Hobby and cultivar notes
The golden barrel is a fixture of collections, rock gardens and public plantings alike, and its bold symmetry makes it a favourite specimen plant. A number of forms circulate in the trade, including short-spined and near-spineless ('nuda'-type) selections, variegated plants marbled with yellow, and occasional crested (cristata) and monstrose forms. Variegated and crested plants generally have less chlorophyll or slower growth and are often grafted onto a vigorous rootstock and given a touch more shade than the plain green form. Propagation of the species is usually by seed, as offsets are produced only sparingly; see also Propagation — offsets for clustering plants.
See also
- Kroenleinia grusonii — the golden barrel cactus, the genus's sole species
- Echinocactus — the genus in which this plant was formerly placed
- Grafting · Soil and potting mix · Watering · Propagation — seed · Repotting