When is a species considered extinct—when it no longer exists in the wild or when it no longer exists at all?
The cactus species Mammillaria tezontle evolved to grow on a mineral produced from lava called tezontle. An exposed piece of tezontle is the only place you will ever find this cactus in the wild. In Mexico, tezontle is extremely useful as a building material because it is strong and lightweight, so it is dug up and used when discovered. In fact, the cactus M. tezontle was discovered and identified as a species at a quarry. With supplies of the rock tezontle dwindling, the cactus is thought to be near-extinct in the wild.
But there are plenty of M. tezontle plants growing all over the world- in clay pots in people's homes. It turns out that the cactus will grow in garden center potting soil formulated for cacti. It has traveled all over by both legal and illegal means. It is not a particularly large, pretty, or useful cactus, but its very rarity drives people to own and propagate it.
That brings up a question of species conservation: Should we keep a species going when its natural environment is completely gone? The cactus Mammillaria tezontle may live forever as a houseplant, but it is only an example that brings up the larger question of polar bears and other familiar creatures. Read the story of M. tezontle at The Walrus. -via Damn Interesting