Golden barrel cactus
The golden barrel cactus is one of the world's most widely cultivated cactuses. Naturally, it is restricted to a tiny area of east-central Mexico in the states of Queretaro and Zacatecas, at altitudes of c. 1,400 metres.
Mature specimens of the golden barrel cactus may reach over one metre in height, with individuals tightly packed together in large clusters. The mature cactus has a distinctive barrel form, with wide, pronounced dark green ribs. The ridge of each rib has a row of discreet clusters of long, yellowish spines and short, golden hairs. In contrast, the pale yellow flowers are relatively insignificant and only start to appear after twenty or more years. The colour and form gives the cactus its common name; the unpleasantness of the spines gives the cactus another of its more amusing common names; mother-in-law's cushion.
The golden barrel cactus is considered Endangered in the wild; after habitat loss, cactus thieves are thought one of the most significant threats. Despite the ease of its cultivation, the slow generation time and the desire among some horticulturalists for large specimens makes the golden barrel cactus a target for illegal collection from natural populations. It has been estimated that there are about 11,000 individuals in the wild but the trend is that wild populations continue to decline in size. Furthermore, the known populations are highly fragmented so gene flow among populations is likely to be limited. This means that genetically there are likely to be many fewer individuals than the number estimated by simply counting the numbers of plants in the wild would suggest.
There is an international ban on the trade in most wild-collected cactus species yet the trade in material of cultivated origin is legal. The challenge is being able to tell reliably the difference between a cactus derived from a cultivated plant and a wild-collected plant; possession of the former is legal, possession of the latter is likely to be illegal. DNA barcoding, where the sequences of small, highly variable pieces of DNA can be used to identify a species or perhaps even a population, may help in reducing illegal collection and the threat this poses for cactus conservation. However, DNA barcoding requires detailed knowledge of genetic variation in populations of wild and cultivated cactuses. Large specimen cactuses in botanic gardens and private collections are also threatened by thieves; DNA barcoding may help with this problem as well.
Further reading
Guadalupe Martinez J et al. 2013. Echinocactus grusonii. The IUCN Red List of Threatened Species 2013.
Preston-Mafham R. & Preston-Mafham K 1992. Cacti: the illustrated dictionary. Blandford Press.
Stephen Harris