Kanaloa, a New Genus of Fabaceae (Mimosoideae) from Hawaii

Abstract

Kanaloa kahoolawensis Lorence & K. R. Wood, a new genus and species of Fabaceae subfamily Mimosoideae tribe Mimoseae, is described from the Hawaiian Island of Kaho'olawe. Based on morphology, wood anatomy, pollen structure, and chromosome number (2n = 28), Kanaloa is described as a monotypic genus of shrubs allied to genera belonging to the Leucaena and Dichrostachys groups of Mimoseae, from which it is differentiated by its tergeminate leaves, monospermous fruits inertly dehiscent along two sutures with the valves separating into inner and outer envelopes, and large cordiform seeds. The new genus is extremely rare and currently known from only two remaining plants on Kaho'olawe, a small, arid, and highly disturbed island. Fossil pollen attributable to Kanaloa has been found in core samples from lowland sites on O'ahu dating to the early Pleistocene. Because of their great isolation and considerable age, the Hawaiian Islands harbor a unique and remarkable flora with a higher degree of endemismabout 90% of the angiosperms-than any comparable area of the world. These islands have been relatively well botanized, and the angiosperm flora of Hawai'i is well known from a modern floristic treatment (Wagner et al., 1990). Therefore, the discovery of an unusual leguminous shrub not assignable to any genus known from Hawai'i was an unexpected surprise, particularly on an island as small and degraded as Kaho'olawe. Kaho'olawe is the smallest of the major Hawaiian Islands (Fig. 1), with a surface area of 116 km2 and a maximum elevation of 450 m. The island is arid due to its low elevation and location in the rain shadow of the much larger Maui. Study of the numerous archaeological sites on Kaho'olawe indicates it was inhabited by Hawaiians from about A.D. 1000, and by the time of Western contact in 1779 much of the island's vegetation had been cleared for agriculture (Kirch, 1985: 144-154). Kaho'olawe was used as a penal colony by the Hawaiian monarchy from 1826 to 1853 after which it was leased for ranching (Perlman, 1992). Although Kaho'olawe proved too dry and barren for successful ranching operations, feral goat and sheep populations became established and devastated the island's little remaining vegetation, resulting in massive soil erosion (Kirch, 1985). During World War II the island was appropriated by the U.S. military for training troops and as a target for ship-to-shore guns and aerial bombing. It is still used as a bombing target by the U.S. Navy. The central plateau of Kaho'olawe now consists of a barren lateritic hardpan whose soil has been lost by erosion. Conservation efforts to restore the island's vegetation and control feral animals are now being undertaken by the Department of Land and Natural Resources of the State of Hawai'i and the Protect Kaho'olawe 'Ohana, a native Hawaiian activist organization. There is currently a movement to return the island to the State of Hawai'i for management by ethnic Hawaiians, practice of Hawaiian culture, and educational purposes. While participating in a botanical survey of Kaho'olawe conducted by The Nature Conservancy of Hawaii in March 1992, the second author and Steve Perlman, field collectors for the Hawaii Plant Conservation Center (HPCC) of the National Tropical Botanical Garden, found an unusual shrubby Fabaceae. Subsequent visits revealed a second individual located nearby. Both plants were confined to native coastal shrubland on 'Ale'ale Stack (Fig. 1), a steep rocky spire almost separated from the main island by erosion (Perlman, 1992). Herbarium specimens were studied by botanists familiar with the Pacific islands' flora and Fabaceae specialists, none of whom recognized the plant. It was also run through the keys in treatments for Hawaiian Fabaceae (Geesink et al., 1990; Rock, 1920) and for all known genera of Mimosoideae (Lewis & Elias, 1981) without arriving at a satisfactory generic placement. An examination of specimens at the BISH, NY, and PTBG herbaria yielded nothing comparable to this extraordinary plant. Subsequent study of the pl nt's morphology, wood anatomy, chromosome number, and pollen has convinced us that it represents a new genus with unclear affinities belonging to subfamily Mimosoideae, tribe Mimoseae. Kanaloa kahoolawensis Lorence & K. R. Wood, gen. et sp. nov. TYPE: Hawaiian Islands. Kaho'olawe: Makawao District, 'Ale'ale stack, near Pu'u Koa'e, mixed native coastal shrubland, 45 m, 18 Mar. 1992, K. R. Wood, S. Perlman, J. Lau & C. Rowland 1733 (holotype, PTBG; isotypes, BISH, US). Figure 2. NOVON 4: 137-145. 1994. This content downloaded from 157.55.39.103 on Tue, 27 Jun 2017 17:57:12 UTC All use subject to http://about.jstor.org/terms