For more than a year, Manuel Sotomayor, President of the Sociedad Potosina de Cactologla, Alberto Arredondo of the Instituto Nacional de Investigaciones Forestales, AgrIcolas y Pecuarias, and Mario Martinez of the Secretaria del Medio Ambiente, Recursos Naturales y Pesca, have been combing the widely varying terrain of the state of San Luis Potosi in a search dedicated to identifying all of the cacti endemic to the state. We are looking forward to the publication of the results

Their most significant find to date, in our minds, is the discovery of two new sites for Ariocarpus agavoides in San Luis Potosi. This species was formerly known only in the state of Tamaulipas, east of and adjacent to San Luis Potosi. The new sites were found on shallow slopes of calcareous stones, in multiple small colonies with no other vegetation.

Fig. 1. A. agavoides at one of the new locations in San Luis Potosi

Fig.2. Left: side view of the spiniferous areole. Right: its longitudinal cross-section.

Fig. 3. Tubercle apices with spines

Many plants grow at both sites, of the order of 20 plants per square meter in some individual colonies. Scarcely any undamaged plants were found, as they are the victims of the destructive feet of grazing goats The neighboring cactus populations include A. retusus, Coryphantha bergeriana, C. palmeri, Echinocactus platyacanthus, Ferocactus pilosus, Mammillaria candida,  M. chionocephala, M. compressa, Myrtillocactus geometrizans, Opuntia imbricata, O. leptocaulis, O. stenopetala, O. tunicata and Thelocactus tulensis. 

The A. agavoides plants at the new locations are characterized by the presence of spines on each tubercle. As a rarity, this phenomenon is not unknown; Ted Anderson, now at the Desert Botanical Garden in Phoenix, took photographs of such a plant found by him, the only one seen at an A. agavoides site near Tula, Tamaulipas, in 1960.

The new locations widely extend the distribution of A. agavoides by about 50 km and substantially reduce the threatened status of this species. The known sites now number six. The discoverers choose to withhold location details to provide a measure of protection from illegal collectors.

Photos: Fig. 1 by M. Sotomayor: rest by the authors