ALIEN FERNS IN HAWAI'I

In May 1983 Robert Hobdy found Nephrolepis hirsutula (G. Forster) Presl 'Superba' growing along the roadside in lower Nahiku by the Makapipi Stream bridge in East Maui (Hobdy 1766, BISH). It was growing among plants of the more common N. multiflora. Three years later, in March 1986, Tim Flynn and Lynwood Hume found another naturalized population of this cultivar in the Halele'a Forest Reserve, Hanalei Valley, Kaua'i, where they described it as common on the banks of a small tributary stream of the Hanalei River (Flynn 1612, PTBG). This robust cultivar has erect fronds covered with hairy-margined scales and pinnae with irregularly undulate or laciniate-lobed margins. This fern was known in cultivation, and specimens of it were collected in Honolulu gardens in 1940 (Neal April 2, 1940, BISH) and again in 1944 (Neal 1246, BISH). Proctor (1977) reported this fern to be common in cultivation in the Lesser Antilles, where it sometimes persisted or spread from abandoned plantings. This is similar to its pattern in Hawai'i, where it does not appear to be an aggressive invader.

It is interesting that the presence of N. hirsutula itself has not been documented in Hawai'i. It is known from Australia and Asia to the Pacific Islands and is very common in Fiji and throughout central Polynesia, and would seem a likely candidate for immigration to the Hawaiian Islands. Reports of its presence in Hawai'i have been based mostly on misidentification of N. multiflora, which, although similar in appearance, can be distinguished by the presence of a row of short, erect hairs on the adaxial surface of the pinna midrib, and also by the appressed or only slightly spreading white to light tan, lanceolate to linear-lanceolate rachis scales with long hairy margins, the hairs often densely interwoven to form a woolly, mat-like covering. N. hirsutula has narrow, linear-lanceolate, often hairlike brownish, hairy-margined scales on the adaxial surface of the midrib, and rusty brown, at times darker in the center, dense rachis scales which have spreading hairy margins, but do not form a woolly covering.