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Rare Delights in Hawai‘i
The locations of nurseries and out-planted sites are not generally advertised for security concerns—I know of only a few. Several of the rare plants described below, however, can be found in botanical gardens open to the general public. When visiting the islands visitors should plan to include stops at the Lyon Arboretum in Honolulu; the McBryde Garden on Kaua‘i’s south coast, home to the largest collection of Hawaiian plants in cultivation—referred to as a “botanical arc”; the Limahuli Garden on Kaua‘i’s north coast, which specializes in endemic species of Kaua‘i; and the small, but botanically very interesting, Maui Nui Botanical Garden in Kahului, Maui. The plants featured below represent only a sampling of the rare (and endangered) plant species on the Hawaiian Islands. They are presented in alphabetical order.
Capparis sandwichiana (Capparaceae) is the only endemic member of this family on the Hawaiian Islands. Readers will be familiar with the caper of culinary use; it is the pickled unopened flower bud of C. spinosa a native of the Mediterranean region. The Hawaiian species is distributed in coastal habitats on all of the main islands. It is categorized as a “vulnerable” species in Hawai‘i, which recognizes the dangers to its habitat presented by development of coastal areas. Photo 4 was taken on the southern coast of Maui near the entrance to the King’s Highway, a trail of historical significance that follows the coastline of southern Maui. In order to see this beautiful plant in flower, visitors should plan to reach the site early as the flower quickly fades in the heat of the day. The site is reached by driving south as far as the paved road allows—to La Pérouse Bay—and then hiking along the coast (Photo 5) until the lava flow is reached, about a mile from the parking area at the end of the road.
Delissea (Campanulaceae), another of the spectacular lobelia relatives of the Hawaiian Islands, is a genus of nine species, seven of which are extinct. The remaining two—perhaps only one—are D. subcordata, last collected on O‘ahu in 1934, and D. rhytidosperma, a rare Kaua‘i endemic known from only a few sites on the island, and now under cultivation at Limahuli Garden. Photo 6 shows a specimen in an early stage of flowering; Photo 7 shows a plant in full flower with some maturing fruits. Delissea is not the only genus within the Hawaiian Campanulaceae that has significant members either at risk or gone altogether. Clermontia, for example, is reckoned to consist of 22 species, three of which are rare with one extinct. Cyanea, the next to largest genus in the Hawaiian flora with 52 species listed in the Manual (as of 1999), consists of 22 species that are not at risk, 16 that are rare or endangered, and 14 that are extinct. The genus Trematolobelia, with four species, appears to be relatively well off with only one of its species listed as rare. An often asked question is: if a species is extinct, how do you know it existed in the first place? Descriptions of many plant species was done by specialists working with dried specimens in museum collections. As seems likely, collectors, not knowing of the rarity of a newly discovered plant, collected every individual they saw. Many of the plants were never very abundant in the first place, and certainly couldn’t stand that sort of sampling. Another reason for extinction is the wholesale loss of habitat caused by land clearance for agriculture; harvesting forests for building purposes, which took most understory plants out with them; and massive development of housing and recreational facilities on the islands.
The Hawaiian Islands are home to one nearly endemic genus and two endemic genera of mints (Lamiaceae = Labiatae): Haplostachys with a single extant species (out of five); Phylostegia, with 27 Hawaiian species (four or five extinct) and one native to Tahiti; and Stenogyne, with 20 species (three or four extinct). Many species in the latter two genera are considered at risk. The only surviving member of Haplostachys, H. haplostachya, honohono in Hawaiian, is the subject here. This species, never very abundant, has been reduced to a single population on Kïpuka kälawamauna on the saddle between Hualälai and Mauna Kea on the Big Island. The name can be divided a bit to show its origin: a “kïpuka” is, among other things, a vegetated island surrounded by lava. The terminal unit “mauna” is the word for mountain; “kälawa” is likely a place name, although there could be a significance of which I am not aware. Access to this area is prohibited except to authorized individuals (one of which I am not). The plant illustrated in Photo 8 was photographed at the McBryde Garden, which is the showcase garden of the National Tropical Botanical Garden (a.k.a. NTBG). Efforts to propagate this species are being made at the rare plant nursery on the Big Island.
Kanaloa kahoolawensis is, with little fear of argument, the rarest of the rare. By one report, we learn that there is a single plant surviving in Nature; by another, two. We won’t quibble; suffice it to say that this species is within one or two plants from extinction in the wild. It is growing well in the collection at the McBryde Garden but its future seems nonetheless in doubt. Although the plant grows well in captivity (Photo 9) and produces flowers (Photo 10), it fails to set seeds because it is self incompatible; it needs a partner! Theoretically, there is the possibility of producing more individuals using sterile culture techniques, but these plants, which would all be derived from the same parent and hence possess the identical genetic makeup of that parent, would also be self incompatible. Kanaloa kahoolawensis is a newly described genus and species of the Fabaceae (Leguminosae)—it was discovered in 1992. It only occurs on nearly inaccessible sea-stacks on the coast of Kaho‘olawe. Its discovery by botanists from the NTBG represented not only a new species but a new genus, a fairly rare find considering the intense level of field activity in the islands for over 250 years. The genus name derives from the Hawaiian name for the island, while the specific epithet comes from the map name of the island. Kanaloa, among other definitions, relates to a major Hawaiian god. The Hawaiian common name for the plant is “Ka palupalu o Kanaloa,” which translates as: the gentleness of Kanaloa. Although Kanaloa is limited to one or two individuals in the wild, there is evidence that it was more widespread at one time. Pollen discovered in cores taken on O‘ahu, Maui, and Kaua‘i were recognized as originating from an unknown legume. It is now thought that that legume was Kanaloa. The species was co-dominant with Dodonaea viscosa (Sapindaceae) and a Pritchardia sp. (Arecaceae = Palmae) (we’ll see both of these in later articles) for a period extending from before 1210 B.C. to 1565 A.D., after which Kanaloa pollen rapidly disappeared, with the other two species declining as well. What caused the plant to disappear remains a mystery: perhaps its habitat came under threat from agricultural activities; perhaps there was a local climate fluctuation. Dodonaea viscosa and several species of Pritchardia remain significant elements in the Hawaiian flora at the present time.
In Munroidendron racemosum (Araliaceae) we meet one of the most elegant of trees. The floral display, a raceme, from which its specific epithet derives, would be an absolute winner were the tree ever to enter the horticultural world. Photos 11 and 12, taken at the Limahuli Garden, show the tree and a close-up of its magnificent floral display. This species is endemic to the nearly inaccessible cliffs of Kaua‘i, and within that area, to only three sites. However, it appears easy to grow, with several very nice specimens available for viewing at the Garden.
Portulaca (Portulacaceae) is represented on the Hawaiian Islands by seven species, three naturalized, one indigenous, and three endemic. All of the endemics are considered rare, the one featured here perhaps the rarest of them all. Although first collected in the early part of the 20th century, P. molokiniensis, ‘ihi in Hawaiian, did not receive official recognition as a species until much more recently. Photos 13 and 14 were taken at the McBryde Gardens; it can also be seen in the Maui Nui Botanical Garden. Access to this plant in its natural habitat, the sea bird nesting islet Molokini (a major snorkeling destination) and two small populations on Kaho‘olawe, is limited to authorized visitors. There are likely no more than 1000 individuals known in the wild; the main threat is from alien species. It is thought that it may have evolved from the endemic, and also rare, P. lutea, with which it can cross. 11/9/06
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