ISI 2017-4. Mammillaria spinosissima subsp. pilcayensis (Bravo) D. R. Hunt

In 2016 we offered a robust form of M. spinosissima with stout upright stems and reddish spination. The subspecies pilcayensis is slightly thinner-stemmed but not enough to explain its tendency to sprawl. There is more at play here, namely an apparent lack of negative geotropism that makes most plants grow upward. However, the precise mechanisms that control this phenomenon remain to be researched. The form offered here is particularly reluctant to stand up straight and will soon arch over the edge of a pot and grow horizontally along the greenhouse bench. Louise Bustard, a former horticulturist at Kew and now Education Officer at the Glasgow Botanical Garden, suggested the solution of planting it upside-down through an enlarged hole in the bottom of a hanging pot. This works well when the plant is small and single stemmed with enough of a root ball to hang on, much as it would in its cliff-side habitat. As the plant starts to branch, repotting can present more of a challenge requiring a pot cut in two then wired back together. We had such a branched specimen reach a length of more than a meter with several side branches. It finally collapsed under its own weight when the roots could no longer hold on resulting in the mauling of an unsuspecting and unarmed variegated Agave attenuata growing beneath it. It was sentenced to be cut and propagated for future distribution so we now have sufficient quantity to realize that goal. Rooted cuts of HBG 59537, a plant from Woody Minnich, acquired by us in the early 1980s. The subspecies is native to the Barranca de Pilcaya in the state of Guerrero, Mexico and the adjacent state of Mexico where this canyon is called the Barranca de Malinaltenango, where it can be found hanging from the calcareous, conglomerate cliffs at ca. 1400 m altitude. $8.

apex side

Photo © 2017 by John N. Trager. Images may not be used elsewhere without permission.

Published in the Cactus and Succulent Journal, Vol. 89 (3), May-June, 2017