One of the rarest of Hawai'i's rare plants is being proposed for the federal endangered species list.

Phyllostegia hispida, a non-aromatic member of the mint family, is so rare it has no common name. It exists only in the wet forests of eastern Moloka'i in the 2,300-foot to 4,200-foot elevation, where the loosely spreading vine forms large tangled masses.

The plant has been seen in the wild only eight times from 1910 to 1979, according to the U.S. Fish and Wildlife Service. Last April, 10 new wild plants were discovered within Pu'u Ali'i Natural Area Reserve.

Seeds and cuttings from those plants are maintained for propagation at the University of Hawai'i's Lyon Arboretum, the National Tropical Botanical Garden on Kaua'i, and Kalaupapa National Historical Park on Moloka'i.

A dozen Phyllostegia hispida grown in captivity were planted in the natural area reserve in April, and all but one were reported to be doing well, according to the Fish and Wildlife Service.

In June, another 12 plants were placed in an enclosure at The Nature Conservancy's Kamakou Preserve, bringing the total number of plants in the wild to 10 naturally occurring and 23 recently outplanted individuals.

Its low numbers are the most significant threat to the species, which make it particularly susceptible to extinction from random events such as hurricanes and disease outbreaks, the service said. Other threats include predation and habitat degradation by feral pigs, competition with invasive non-native plants, and possible predation by invertebrates such as slugs.

Phyllostegia hispida has been a candidate for listing under the Endangered Species Act since 1997.

The Fish and Wildlife Service is seeking public comment on the proposed rule to list Phyllostegia hispida as endangered. The service said it is especially interested in receiving information on any threats to the species; additional information concerning its range, distribution and population size, including the locations of additional populations; and current or planned activities in the areas occupied by the species and possible impacts.

The deadline for comment is April 21. Comments can be sent via the Federal eRulemaking Portal at www.regulations.gov; or by mail to: Public Comments Processing, Attn: RIN 1018-AV00; Division of Policy and Directives Management; U.S. Fish and Wildlife Service; 4401 N. Fairfax Drive, Suite 222; Arlington, VA 22203.