Two species of echinocactus are found in the Big Bend area - e. texensis, which has pronounced ribs and very heavy, sharp spines, and the slightly less threatening e. horizonthalonius where most spines lie against the body, apart from the central spine which points out and downwards. The growing tip is buried beneath a distinctive mat of woolly hair, from which brilliant pink flowers emerge in springtime. The Turk's head cactus is found in most areas of the park below around 5,500 feet.