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 illegal logging of tropical forests, which has accelerated in the island nation in recent years. (See video: "The Smallest Lemur.")

View Images The large-bodied indri—the largest species of lemur—is classified by the IUCN as critically endangered. PHOTOGRAPH BY NICK GARBUTT

Temperate slipper orchids, whose slipper-shaped flowers make them a popular ornamental plant, face a similar fate, with 79 percent of species threatened with extinction, according to the IUCN. The flowers are found across North America, Europe, and Asia and are at risk because of habitat destruction and overcollection. (See: "Orchid flowers fool flat-footed flies by faking fungus-infected foliage.")

View Images The California lady's slipper, found only in California and Oregon, is classified by the IUCN as endangered. PHOTOGRAPH BY BILL BOUTON

"What was most surprising about this assessment was the degree of threat to these orchids," said Hassan Rankou, the IUCN Species Survival Commission's Red List Authority for the Orchid Specialist Group, which is hosted by the U.K.'s Royal Botanic Gardens, Kew.

"Although the industry is sustained by cultivated stock," he said, referring to the trade in orchids, "conservation of wild species is vital for its future." (See National Geographic's photos of orchids.)

In its latest update, the IUCN added a number of new species to its Red List and reassessed the conservation status of many species placed there years ago.

Five notable examples:

1. Japanese Eel

View Images The Japanese eel, the most expensive fish on the menu in Japan, is classified as endangered. PHOTOGRAPH BY YUICHI KANO

The Japanese eel was added to the IUCN's list with an endangered classification, meaning it has a high risk of extinction.

A delicacy in Japan, this commercially lucrative fish has been hard hit by a combination of overfishing, habitat loss, pollution, and changes in ocean currents. (See "Mystery Travelers" to learn more about eels.)

"While the status of this species is of great concern, the assessment of the Japanese eel and other eels is a hugely positive step," says Matthew Gollock, chair of the IUCN Anguillid Specialist Sub-Group.

"This information will allow us to prioritize conservation efforts for eel species and the freshwater ecosystem more broadly."

2. Brazilian Three-Banded Armadillo

The Brazilian three-banded armadillo—currently serving as the 2014 FIFA World Cup mascot—was reassessed by the IUCN team and remains vulnerable, meaning it has a high risk of becoming endangered.

The species has declined an estimated 30 percent in the past 10 to 15 years, primarily because of extensive conversion of its habitat in Brazil to sugarcane and soybean plantations.

3. Chinese Crocodile Lizard

The Chinese crocodile lizard, found only in China and Vietnam, was newly classified as endangered because the species is thought to have declined by 84 percent from 1978 to 2008 and only a few isolated populations remain.

One of the primary threats to the species comes from illegal hunting for the international pet trade, with habitat loss being an additional factor. (See "The Kingpin" to learn more about Asia's wildlife trade.)

4. Banana Orchid

The banana orchid, another new addition to the IUCN Red List and the national flower of the Cayman Islands, was classified as endangered because it is currently losing habitat at a rapid rate.

The dry forests and shrublands where it lives are being cleared to make way for housing and tourism development, and—unless conservation measures are taken—it is likely to lose 50 percent of its habitat within the next century.

5. Yarkon Bream

View Images The Yarkon bream, found only in Israel, went from being extinct in the wild to vulnerable, according to the IUCN. PHOTOGRAPH BY MENACHEM GOREN

Not all of the changes to the Red List were negative, however. The Yarkon bream, a fish found in Israel, stands out as a conservation success story. The species jumped multiple levels on the IUCN classification system, going from extinct in the wild to vulnerable.

The Yarkon bream disappeared from the wild in 1999 after the only remaining individuals (120 of them) were saved from a riverbed that was drying up due to drought.

A successful captive breeding program was started at Tel Aviv University and, seven years later, 9,000 fish were released into their native habitat, where their descendants are thriving today.