August 2017 Plant Highlight: Gymnocalycium schickendantzii ssp. delaetii

by Brian Kemble

Gymnocalycium is a fairly large genus of South American cacti, with about 50 currently recognized species plus a number of subspecies. The majority of the plants are found in Argentina, but they extend northward into Uruguay, Paraguay and Bolivia. For the most part these are dome-shaped or globular cacti, but some are flattened and a few are short-columnar. The various species may be single or clustering, and the size of a single head ranges from smaller than a ping-pong ball to the size of a soccer ball. Gymnocalycium spines vary wildly, with some being ferociously spiny and others having spines reduced to little squiggles pressed against the body of the plant. One of those with stout spines is Gymnocalycium schickendantzii ssp. delaetii, from northwestern Argentina.

Like many other plants in the genus, Gymnocalycium schickendantzii ssp. delaetii has a dome-shaped body, with mature plants attaining a diameter of 8 to 12 inches (up to 30 cm) and remaining single. In the shade, plants are deep green to bluish-green, but in sunnier situations they take on brown or bronze tinges. Each areole (the “eye” from which the spines and flowers emerge) puts out about 8 heavy spines which arch outward in all directions, intermeshing with those from adjacent areoles. The result is a well-armed plant, but with enough space between the spines that the plant body is readily visible. While the new spines are black or brown, they soon lighten to gray.
Gymnocalycium schickendantzii ssp. delaetii is summer-blooming, with flowers emerging mainly in December and January in its native habitat in Argentina. Of course, the seasons are reversed in California, and at the Ruth Bancroft Garden our plants flower from June to August, sometimes extending into the fall months. As with other species of Gymnocalycium, the buds of G. schickendantzii ssp. delaetii are covered with smooth overlapping scales. They open into funnel-shaped flowers which are off-white or flushed pink and about 2 inches long (5 cm). Though the plants flower over an extended period, there are never more than a few flowers open at any given time.

Although our plants at the Ruth Bancroft Garden have not made fruits, a successfully pollinated flower yields a club-shaped or barrel-shaped fruit which is blue-green at first, ripening to red. On the inside, the fruit is filled with a viscous translucent liquid containing many small black seeds. At maturity, the fruit splits open.

G. schickendantzii ssp. delaetii comes from a summer-rainfall area, but it can be grown outside in our winter-rainfall climate if given sharp drainage and occasional water during the summer months. It can endure cold spells down to the low 20’s F (-6 C).

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