Asplenium-leaved Diellia

Diellia erecta

Description

Diellia erecta, a member of the spleenwort family, is a fern that grows in tufts of three to nine lance-shaped fronds (large divided leaves), each 8-28 in (20.3-71.1 cm) long. The fronds emerge from a 0.4-1-in-long (1-2.5-cm-long) rhizome covered with brown to dark gray scales. The frond stalks are reddish-brown to black, smooth and glossy, 0.8-8.3 in (2-21.1 cm) long, and have a few stiff scales at their bases. Each frond has 15-50 lance-shaped pinnae (leaflets) arranged oppositely along the midrib. The pinnae are usually 0.8-1.6 in (2-4.1 cm) long and 0.2-0.3 in (5.1-7.6 mm) wide. Ten to 20 sori (spore-filled clusters), which may be separate or fused, are borne on each margin of the pinna. Each sorus is covered by a protective membrane that falls short of the edge of the frond and runs parallel to the edge of each pinna. This species differs from other members of the genus in having brown or dark gray scales usually more than 0.8 in (2 cm) in length, fused or separate sori along both margins, shiny black midribs that have a hardened surface, and veins that do not usually encircle the sori.

D. erecta was described by William Dunlop Brackenridge in 1854 based on a specimen collected during the Wilkes Expedition 14 years earlier. Current authorities consider D. erecta to be a species with no subspecific designations.

Habitat

D. erecta is found in Diospyros sandwicensis (lama)/'ohi'a lowland mesic forests 700-5,200 ft (213.4-1,585 m) in elevation. Other associated plant species include Dodonaea viscosa ('a'ali'i), Dryopteris unidentata, Pleomele auwahiensis (halapepe), Syzygium sandwicensis ('ohi'a ha), and Wikstroemia sp. ('akia).

Distribution

D. erecta was known historically from the Kokee area on Kauai; the Koolau Mountains on Oahu; Kahuaawi Gulch, Puu Kolekole, Pukoo, Pelekunu Valley, and Kaunakakai Gulch on Molokai; Mahana Valley and Hauola Gulch on Lanai; scattered locations on Maui; and various locations on the Big Island of Hawaii.

The species is currently known from Molokai, Maui, and Hawaii, with a statewide total of six to seven populations that contained approximately 34-36 individuals in 1997.

Threats

The major threats to D. erecta are (1) habitat degradation by pigs, goats, and cattle; (2) competition with alien plant species; and (3) stochastic extinction due to the small number of existing individuals.

Feral pigs are a major threat on the island of Hawaii to populations of D. erecta in the regions of Manuka and Honomalino in the South Kona District, and their activities also threaten one population of this species on Molokai.

Goats threaten two populations of D. erecta in Halawa Valley and Puu Kolekole on Molokai. On both East and West Maui, populations of D. erecta continue to be threatened by habitat damage caused by grazing cattle.

D. erecta is not known to be unpalatable to cattle, deer, and goats; as such, predation is a probable threat to this plant at sites where these animals have been reported.

One population of D. erecta at Halawa Valley on Molokai has been damaged by Christmas berry. Christmas berry is spreading on East Maui in Iao Valley and on the south slope of Haleakala Volcano, proving in both places to be one of the primary alien plant threats to the populations of D. erecta there. On the island of Hawaii, Christmas berry continues to threaten at least two populations of this species in the regions of Manuka and Honomalino in the South Kona District.

Strawberry guava is beginning to invade the habitat of populations of D. erecta on East Maui and on Molokai. At least one Molokai population of D. erecta is being negatively affected by molasses grass. Molasses grass is spreading quickly throughout the dry regions of West Maui, threatening two populations of the species there.

Conservation and Recovery

Living Indigenous Forest Ecosystems, a community-based nonprofit corporation, manages conservation lands at Kahikinui Forest Reserve; in July 1997 it fenced a portion of the forest reserve that harbors a population of D. erecta. Follow-up monitoring will be conducted annually or biannually. It is expected that this action will enhance conservation of the D. erecta plants growing there.

A fence that was built in the 1980s protects the population of D. erecta in the Manawainui Plant Sanctuary. The Native Hawaiian Plant Society conducts periodic weeding at this site.

An unspecified number of spores are in storage at the National Tropical Botanical Gardens.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

Pacific Remote Islands Ecological Services Field Office
300 Ala Moana Blvd., Room 3-122
P.O. Box 50088
Honolulu, Hawaii 96850
Telephone: (808) 541-1201
Fax: (808) 541-1216

Reference

U. S. Fish and Wildlife Service. 10 November 1994. "Endangered Status for 12 Plants from the Hawaiian Islands." Federal Register 59 (217): 56333-56351.