Sand Dollar Cactus

Reproduction takes place via sexual outcrossing through cross-pollination; star cacti reach sexual maturity after a few years, when they have attained 2 - 3 cm in diameter (2). Flowers are produced from March to June and fruiting occurs from April to June; the specific pollinators have not been identified but are thought to be insects (5).

International trade in wild-collected star cacti is prohibited by its listing on Appendix I of the Convention on International Trade in Endangered Species (CITES) (3). This species is also protected under Mexican law and is listed as Endangered by the U.S. Fish & Wildlife Service (6). Star cacti have been grown in cultivation since the 1840s and are now widely propagated from seed; it is hoped that this will help alleviate the pressure on wild populations of this cactus (2). The U.S. Fish & Wildlife Service have drafted a Recovery Plan in an attempt to secure the future of this species (5). The Recovery Plan highlights the need to protect existing populations, carry out research into possible new populations and to develop a formal conservation agreement between the United States and Mexico (5).

This small, round cactus is low-domed and spineless, resembling a dead, spineless sea urchin in appearance. The disc-shaped body is divided into 7 - 10 sections, known as ribs; in the middle of each rib there are woolly areoles (2). The body is a greenish-brown colour and may appear speckled from its covering of white scales (4). The flowers of this cactus are yellow with red bases and the outer parts are very woolly (2). Green to pink oval fruits are produced; the outside coat is covered with woolly hairs (4).

Today this species is associated with thorn scrub, amongst rocky ground; it may have previously occupied richer, flat grasslands that have since been developed (2).

Star cactus is found in the state of Texas in the United States (1) and in Mexico, to the east of the Sierra Madre Oriental mountain range (2). Previously more abundant, this species is today restricted to a single 200-acre site in Texas, where there are around 2,000 individuals (5), and a few small sites in the state of Tamaulipas, Mexico (7).

Classified as Vulnerable (VU - B2ab(v)) on the IUCN Red List 2002 (1), and listed on Appendix I of CITES (3).

The star cactus is now extremely rare in the wild, and only a few widely separated populations are known to persist today (2). This attractive and unusual cactus has been highly valued in the commercial cactus trade and over-collection has resulted in the local extinction of some populations. Despite protection, illegal collection continues to threaten the future of this species (4). Habitat destruction has been, and remains, the major cause of the decline in this species; vast areas have been converted to agriculture and road construction (5). In Texas, mechanical and chemical bush clearing techniques together with the introduction of invasive grasses have had devastating effects (5).