Kroenleinia grusonii

Kroenleinia grusonii belongs to the small genus Echinocactus, which together with the related genus Ferocactus, are commonly referred to as barrel cacti. The species was first described by German plantsman Heinrich Hildmann in 1891. While sometimes referred to as golden ball, this species is not to be confused with Notocactus leninghausii which have fuzzy, harmless spines and are native to Brazil and Paraguay.

Recent phylogenetic studies have found that Echinocactus grusonii is probably polyphyletic with respect to the rest of Echinocactus, and is probably derived from hybrids between Echinocactus and Ferocactus. To correct this, Echinocactus grusonii has been moved to its own genus, and under this scheme the correct name would be Kroenleinia grusonii Lodé.[2] However, not all authorities have accepted this move so far.[3]

Growing as a large roughly spherical globular in shape, generally solitary, although basal shoots may sprout from adult specimens, Kroenleinia grusonii may eventually reach over 1 metre (3.3 ft) in height after many years with a diameter of 40 to 80 centimeters. The duration of a generation is estimated at 10 years. Younger Golden Barrel plants do not look similar to mature specimens. The generation lifetime is estimated to be 30 years.[1]

There may be up to 21-35 pronounced ribs in mature plants, though they are not evident in young plants, which may have a knobbly appearance.The areoles are yellow woolly when the plant is young, then whitish and finally greyish. The sharp spines are long, straight or slightly curved, and various shades of yellow or, occasionally, white. They are large and are 1 or 2 cm apart from each other. The radial spines are arranged in numbers between 8 and 10, and measure more than 3 cm in length. The central ones, between 3 and 5, measure about 5 cm; They are strong, striated and straight, although the central ones may be slightly curved downwards.

Small yellow flowers appear in summer around the crown of the plant, but only after twenty years or so. They are 4 to 6 centimeters long and 3 to 5 centimeters in diameter. The flowers only appear on older specimens and last 3 days. The spherical, somewhat elongated, greenish fruits are covered with white wool. They are 1.2 to 2 centimeters long and contain smooth, shiny brown seeds.[4]

Golden barrel cacti at the Huntington

Kroenleinia grusonii is widely cultivated by specialty plant nurseries as an ornamental plant, for planting in containers, desert habitat gardens, rock gardens, and in conservatories.[5] A white-spined form, and a short-spined form, are also in cultivation.

It is one of the most popular cacti in cultivation and has increasingly become popular as an architectural accent plant in contemporary garden designs.

The cactus is considered easy and relatively fast growing in warmer climates around the world. The plants do have some basic requirements; an average minimum winter temperature of 12 °C (53.6 °F); and good drainage with less watering in winter.[5] Excess water in cool periods may lead to rot. Golden Barrels are hardy to about −8 °C (15 °F) for brief periods.

Beyond Central Mexico, Kroenleinia grusonii specimens may also be seen in collections of desert plants in many botanical gardens. In the UK it has gained the Royal Horticultural Society’s Award of Garden Merit.[6][7]

• 
  Mature golden barrels showing their distinctive clustering habit. Photo from the Huntington Desert Garden in California.
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  Closeup of the top.
• 
  Kroenleinia, a nearly spineless form
• 
  Kroenleinia grusonii spine detail at the United States Botanic Gardens
• 
  Stereoscopic crossview of a golden barrel cactus.
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  Spine detail
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  Flower detail
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  Fruit detail
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  Seeds
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  Mature golden barrel in cluster form in a greenhouse in Kalimpong

• Cacti of Mexico

• Preston-Mafham, Rod & Ken (1992). Cacti: The Illustrated Dictionary. Blandford Press. ISBN 978-0-7137-2092-1.

• Media related to Kroenleinia grusonii at Wikimedia Commons
• Data related to Kroenleinia grusonii at Wikispecies