Cactus  (Ariocarpus trigonus)

This striking cactus is only visible from its claw-like tubercles that emerge through the soil; the majority of the stem remains hidden underground (2). Unusually amongst cacti, the yellow-green plant is spineless, lacking areoles on the smooth upper surface of the tubercles (2). Lemon-yellow flowers emerge in a ring on the crown of the stem and when fertilised these develop into small white berries (5).

Found over a fairly wide geographical range in northeastern Mexico, from the eastern edge of the mountains of the Sierra Madre Oriental, and concentrated in the Valley of Jaumave in the state of Tamaulipas (2).

Ariocarpus trigonus inhabits dry thorn forest and scrubland amongst very rocky soil, or limestone gravel. It is found on low hills, at altitudes between 200 and 800 metres above sea level (2).

This cactus flowers between September and December, fruits develop in the spring and the rains (which begin in May) help to disperse the seeds by washing them from the centre of the plant (2).

Members of the genus Ariocarpus are known as 'living rock' or 'fossil cacti' due to their unusual appearance (5), and they have been widely in demand from collectors for this reason (2). The demand for this species for the commercial cactus trade is a significant threat to its survival together with the development of the land for agriculture. Large areas of land have been converted for citrus plants or irrigated for cereal crops, and non-developed areas are often occupied by goats, which graze and trample on this species (2).

Ariocarpus trigonus is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), which bans international trade in this unusual cactus based on wild plants (4). The Valley of Jaumave is home to many unusual and rare species of plants and animals and it has been suggested as an excellent candidate for a nature reserve (2).

Authenticated (20/3/03) by Dr Nigel Taylor, Royal Botanic Gardens, Kew.
http://www.rbgkew.org.uk