Notes on the Rediscovery, Status, and Ecology of the Very Rare Hawaiian Fern Christella boydiae (Thelypteridaceae)

Abstract

The genus Christella (Thelypteridaceae) is comprised of approximately 50 species distributed predominantly in the Old World tropics but also in the Americas (Holttum 1977). Two native Christella species, C. cyatheoides (Kaulf.) Holttum and C. boydiae (Eaton) Holttum occur in Hawai'i (Wagner, 1981). Christella cyatheoides is a common and characteristic component of matted fern understory of Hawaiian rain forest. Christella boydiae is a much rarer diminutive species of rocky stream courses. Christella boydiae has been collected only from the Ko'olau range of O'ahu, Kipahulu and Waiho'i Valleys on East Maui, and along low elevation watercourses near Hilo on Hawai'i. Currently it is only known from one of these historic populations at Kipahulu Valley. There are 20 specimens of C. boydiae in the Bernice Pauahi Bishop Museum Herbarium Pacificum (BISH) that represent 18 or fewer collections. Most of these specimens are in poor condition and as typical of collections made prior to 1910, have little or no collection information. The species has been most often collected on O'ahu. Of these, six specimens (one third of the total at BISH) were made between 1900 and 1908 by either of the noted Hawaiian botanists, C.N. Forbes or J.F. Rock, mostly from the Punalu'u region of the Ko'olau range. The last collection of Christella boydiae on O'ahu was made prior to 1908. However, Warren H. Wagner found that this species was still present in the Punalu'u area of the Ko'olau range on O'ahu as late as 1965 (Kaluanui Stream, rock shelves, Castle trail, Hau'ula Forest Reserve, Ko'olau range, W H. Wagner and S. Carlquist 65270 MICH). Since that time, many exotic weeds, noteably Clidemia hirta (Melastomataceae), have invaded the area and this species has apparently disappeared. On Hawai'i island, the species, to our knowledge, has been collected only once. Until recently, Christella boydiae had been collected only three times on Maui, first in 1881 in Kipahulu Valley (EL. Clarke s.n., BISH) without further location information. Then after 86 years, C. boydiae was again collected in Kipahulu Valley in 1967 (R. DeWreede 30) along Palikea stream at 915m (Lamoureux, 1968). A third Maui collection was made in 1973 in adjacent Waiho'i Valley as part of the NSF-sponsored Waiho'i Valley Research Project (B. Harrison 10) at 915-1040 m along Waiohonu stream where it was a rare fern from a shady location under a ledge associated with hymenophyllaceous ferns and various mosses along the stream bank (B. Harrison-Gagne, pers. comm.). Neither of these collections is present in the cabinets at the Herbarium Pacificum (BISH): although the latter is in the University of Hawai'i collection. Fourteen specimens at the Herbarium Pacificum (BISH) include the year of collection. Of these, eight were collect86