112 TE FERN GENUS NEPHROLEPS N HAWA Charles H. Lamoureux Department of Botany University of Hawaii at Manoa 3190 Maile Way Honolulu, Hawaii 96822 NTRODUCTON Nephrolepis is a genus of about 30 species of ferns, of mainly pantropical distribution but extending both north and south to as much as 40 latitude. The generic name ("kidney scale") refers to the kidney-shaped indusium possessed by most of the species. Comnon names frequently used are Sword fern, Boston fern, 'Okupukupu, and Ni'ani'au. The genus is morphologically quite distinct and easily defined: Stem a short, erect stock with closely tufted fronds; also having slender lateral branches (runners) bearing numerous roots and occasional buds which develop into new plants. Fronds typically long and narrow ("Sword-shaped"); once-pinnate (except in some cultivars); pinnae articulate to the rachis, falling singly; stipe persistent, not articulate to the stem; pinnae with free veins, often with a scalelike deposit of calcium carbonate at the end of each vein on the upper surface of the pinna. Sari usually single and terminal on each vein on the lower surface or near the margin, of the pinna, protected by a kidney-shaped or orbicular indusium; (one or two species have a continuous marginal sorus and a linear indusium). NEPHROLEPS N HAWA There are three species of Nephrolepis now growing wild in Hawaii. N. cordifolia (L.) Presl. is typically found in shade in wet forests between 1000 and 5000 feet altitude, often growing as an epiphyte, but sometimes on rocks and rarely in soil. t is known from Kaua'i, both ranges of 0'ahu, Moloka' i, Maui, Uma' i, and Hawai' i. The species, at least in the broad sense, has a pantropical distribution, extending north to Japan and south to New Zealand. The fern has relatively narrow fronds (pinnae are typically less than 30 mm in length), and bears tubers on its runners (although only about 1 in 10 Hawaiian plants typically has such tubers, and only about 1 in S herbarium specimens retain them). These are the two characters most often used in keys to separate this species, but neither is
113 particularly useful. As Fig. 1 indicates, the other Hawaiian species of Nephro1efif often have short pinnae; also the tubers are rarely present. Two of t e best characters for recognition of N. cordifo1ia are the scales and the three-dimensional shape of the pinnae. The scales on the stipe are copious, spreading, chestnut brown, and 1anceo1ate;cllose on the rachis are copious, 1inear-lanceolate, long-attenuate, with a dark basal spot. The pinnae are usually glabrous, and the fertile paeare slightly revolute at the margins and appear bullate..since this character often disappears on pressing, the scales are the most useful diagnostic feature in herbarium material. The pantropica1 Nephro1epis exa1tata (L.) Schott has a somewhat wider ecological amplitude, growing from sea level to about 5000 feet in a variety of habitats, both sunny and shaded, typically rooted in soil or among rocks, not usually growing epiphytically. t has been collected on the six large forested islands and on Ni'ihau. t is generally a larger plant with broader fronds than N. cordifolia. n Hawaiian material the stipes typically lose most oftheir scales early; the scales are spreading, chestnut brown, and lanceolate. The rachis usually retains a few irregularly shaped concolorous scales. The pinnae are glabrous, ad fertile piae are plane, not bullate. Nephrolepis multiflora (Roxb.) Jarrett ex Morton (usually called N. hirsutula (Forst.) Presl in the Hawaiian literature) grows from sea level to about 4000 feet, also in a variety of habitats. t is particularly common asa colonizer of new lava flows, in disturbed sites, on roadsites, and in similar places, often in full sun. t has.now been found on all 8 of the major island$ and Sheila Conant (personal col11tllll1ication) has recently discovered it on Nihoa. t is an extremely variable species: in full sun on recent lava flows mature specimens may be only 15 em tall with short, imbricate pinnae; in shady forests plants 2 m tall with spreading ;pinnae over 100 rnm long are more typical. This is a species from the Old World Tropics. now widely naturalized in the New World. t can be most easily recognized by its scales. t has tightly appressed stipe scales with dark brown centers and white margins. On the rachis it has a variety of scales including SOre that are white and cobwebby. The pinnae bear variously both tawny linear scales and tawny or white cobwebby ones. An important diagnostic feature, which separates N. multiflora from N. hirsutula, is the presence of short, erect hairs-on the upper side of the pinna midrib in multiflora (Morton, 1974). There is one other Nephrolepis which has become naturalized in a limited way. This is the fishtail fern, Nephrolepis biserrata (Sw.) Schott cv. 'Furcans'. t has been found to persist after cultivation, and perhaps even to spread to a limited extent, at Wailau, Mo10ka'i (Fosberg, 1943), Wainiha and Hanakapi'ai, Kaua'i, and Hana, Maui (Wagner, 1950). Fosberg (1943) has reported one collection of N. biserrrata sensa str. from the Ewa Plain O'ahu, in 1936. This-Species is native on other Pacific slands and could conceivably be native in Hawaii. However have examined his collection (FRF 12806) and redetermined it as N. multiflora.
114 The well known Boston fern, and a number of other fancy Nephrolepis grown in Hawaiian gardens and nurseries are cultivars derived fyom N. exaltata. Finally, a curious sterile fern with orbicular pinnae less than 1 cm in diameter is sometimes grown here. t is N. cordifolia cv. 'Duffii'. HSTORY OF NEPHROLEPS N HAWA Fosberg (1943) and Wagner (1950) have also previously reviewed this topic. Nephrolepis exaltata was collected by David Nelson in 1779 (St. John, 1978), and both N. exaltata and N. cordifolia specimens are well-represented 19th century collections. Hillebrand (1888) included only N. exaltata in his flora, but indicated in the discussion (p. 579) that he had two fotns. "One small and narrow, with fibrillose rachis and oblong obtuse pinnae, th lowest gradually dwarfing; the other larger and broader with naked rachis, the frond almost truncate at the base or only slightly narrowing, the pinnae falcate, acute." Clearly the former was the plant now known as N. cordifolia, the latter N.exaltata. Both species seem best interpreted as indigenous native species. Bailey (1883) first reported N. hirsutula (= N. multiflora?), but it is questionable exactly whahe had. The first collection known was made by Topping in 1923 on O'ahu. Subsequently it was first collected on Hawai'i in 1927, Ni'ihau and Kaua'i in 1947, Moloka'i in 1948, Maui in 1951, Lana'i in 1963, and Kaho'olawe in 1980. t is now an abundant fern (Fig. 2), even; though in 1950 Wagner indicated that it was still livery localized." t is not yet clear whether it is displacing N. exaltata or other native ferns. - ACKNOWLEDGEMENTS This study was supported by a grant from Pacific Tropical Botanical Garden. would like to thank Jane Medler for her assistance.
115 LTERATJRE CTED Bailey, E. 1883. Hawaiian ferns, a synopsis. Honolulu: 1. Thrum. 62 pp. Fosberg, F. R. 1943. Notes on plants of the Pacific slands-. Torrey Bot. Club, Bull. 70: 386-397. Hillebrand, W. 1888. Flora of the Hawaiian slands. Heidelberg: Carl Winter. xcvi + 673 pp. Morton, C. V. 1974. William Roxburgh's fern types. Contrib. U. S. Nat. Herb. 38(7). St. John, H. 1978. The first collection of Hawaiian plants by David Nelson in 1779. Hawaiian Plant Studies 55. Pac. SCi. 32(3): 315-324. Wagner, W. H., Jr. 1950. Ferns naturalized in Hawaii B. P. Bishop Mus., Occ. Pap. 20(8): 97-121.
116 70 N.cordifolia (n=66,=23.2, S=0.6) 60 (f) z w Q.. (f) lj... o W (!) z wua::: w Q.. 50 40 30 20 10 N. exaltata (n =102, X =41.0, Sx =1.3) {j......'.!a {j." "' "" \ l"" /c. N. multiflora (n =72, x=59.3, Sx =3.2) P, /' 1/', \, /1 - -C /" "'c / "', c ',c-'-c'-'c, o '--<.)::'...l _"'_...L.-_-'--_-'-D-.L.-_"----J'{j. i' -Do /0 20 30 40 50 60 70 80 90 100 110 120 130 1 1 9 19 29 39 49 59 69 79 89 99 109 119 129 139 140 1 149 LENGTH OF MDDLE PNNA (mm) Fig. 1. Lengths of middle pinnae from Hawaiian Nephrolepis.
117 60 r-----,r---;---,------,---r---...,.---,...---...---... 2 ljj U E a. 40 20 - Nephrolepis cordifolia (n 78) O'-L.L..t;.&...L-:-"'-'<..LL.L...-J..-L.. L---l...---L-:L4...L-s.L..L...l...-JLU'-L-.l..-'LLL.4-.l.-k'LLL.:.L.J 100r-----,----r--...,...--------.-----r------.-----.------...-----. 80 Nephrolepis exaltata (n 119)... 60 Z W U 0:: W a. 40 20 o L.--L<.L.U.:.L-J.--"-'<..LL.L...-J...:..'-.U---l...-::L""-'L---L-...LL L.L...L-..t::.L.:::LLL...L-t:LU.l..-:LLL.a..._.l.-k'LLL.4._l 60.-----,------r--...,...---..,.-----,-----.----...----...----..... Z W w a. 40 20 Nephrolepis multiflora (n 1187) PRE 1900 1900 1909 1910 1919 1920 1929 1930 1939 1940 1949 1950 1959 1960 1969 1970 1979 Fig. 2. Change in frequency of collection of Nephrolepis species with time.