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Plant Highlight: Echinopsis formosa

Ball like cactus growing close to each other

May 2013

Northwestern Argentina is home to a wide assortment of wonderful cacti, many of which have sufficient cold-tolerance to endure even our coldest winters in Walnut Creek, when temperatures plunge to 20-25° F (-4° to -7° C). Among these are many species of Echinopsis. The genus Echinopsis as recognized today includes cylindrical-stemmed plants formerly placed in Trichocereus or Helianthocereus, small globular plants formerly placed in Lobivia, and the South American barrel cacti formerly placed in Soehrensia. Among the latter group is a densely spined species named Echinopsis formosa, which may be single or make offsets to form a cluster. The flowers are normally yellow, though orange and red-orange plants have also been reported.

A close up of a cactus's bright yellow flowersAt the Ruth Bancroft Garden we have several plants of Echinopsis formosa. Some of these, formerly known by the name Soehrensia ingens, are clustering round-bodied plants with honey-colored spines. Others, formerly called Soehrensia formosa, are short-cylindrical, single, and have whitish spines. The largest plants of each kind have attained a diameter of 16” (41 cm), and the tallest of the cylindrical ones has reached a height of 28” (71 cm). These are slow-growing plants, and iA round cactus with bright yellow flowers bloomin on top of itt has taken over 30 years for them to reach this size.

Echinopsis formosa is a spring bloomer, flowering at the Ruth Bancroft Garden in late April and May. The large yellow funnel-shaped flowers are up to 3½” across (9 cm). Our plants took a long time to reach flowering size, but now that they are mature they put on a dazzling show each year.  In nature, they grow in the eastern foothills of the Andes, to the west and northwest of Buenos Aires.