Entire branches of the tree of life are in danger of being wiped out: The majority of species in some groups of plants and animals are now on the "Red List" of the world's most threatened species.

The list, which is managed by the International Union for Conservation of Nature (IUCN) and was updated this week, shows that among the groups most at risk are lemurs and temperate slipper orchids.

Found only in Madagascar, 90 of the 101 species of lemur are threatened with extinction, the IUCN said. More than 20 percent of these small primates are listed as being critically endangered, meaning that they have a very high risk of extinction in the wild. The main threat stems from