Certainly worthy of our attention and appreciation is the native Hawaiian Hibiscus arnottianus A. Gray (family Malvaceae), a small tree from the mountain forests of O'ahu and Moloka'i, known there as ke'oke'o, hau hele, and by several other vernacular names. A grouping of half a dozen individuals is planted between the old and new parts of the Hawaiian Section at MEMBG, and every year in late summer through early fall these plants produce a spectacular exhibition of large white flowers, 13 to 18 centimeters across! Surely passersby along South Tiverton must be admiring this species that flowers over the western perimeter fence.
So recognizable to the general public is hibiscus that few people would have difficulty identifying this to its genus, which includes 220 species worldwide. The Hawaiian Islands have ten species of Hibiscus in the flora, including three that were introduced and became naturalized from cultivation and one, H. tilaceus, a very widespread species of the Pacific Basin and elsewhere along saltwater coastlines and brackish river banks. Hibiscus arnottianus, however, is not commonly found in subtropical landscaping, although it definitely should be and could become a popular plant of Southern California horticulture. Mildred Mathias (1982, Flowering Plants in the Landscape) certainly thought so.
Our mature plants with dull-gray bark are 6 to 8 meters in height, and their shoots are clothed with evergreen leaves. The typical leaf on our plants has a broadly ovate blade 10 to 16 cm in length and a petiole 4 to 7 cm in length. The glabrate (nearly hairless) blade has a shallowly crenate margin and five prominent veins (sometimes also two faint ones) arising at the base, i.e., it has palmate venation. Veins on the lower side, and somewhat on the upper side, are current-red, as are the petioles and young stems. Quite attractive. Attached to each petiole of emerging leaves is a pair of red, narrow (filiform), hairy stipules that soon abscises. The entire shoot is somewhat plagiotropic, i.e., flattened, probably due to the shading on this plant and by the plant canopy of its own lower shoots. The flora of the Hawaiian Islands (Wagner et al. 1990. Manual of the Flowering Plants of Hawai'i) recognizes that this species is highly variable, so that our specimen likely is some intermediate form, but the leaves certainly are not coriaceous (leathery), as described in the flora.
One grows this plant primarily for the showy, solitary flowers. Like its close cousins, H. arnottianus has the lower portion of the corolla fused into a floral tube, here nearly 3.5 cm in length. Above it spread five obovate petals (corolla lobes). The corolla is white, with palmate veins that are pale pink on the underside, so that the corolla may appear pinkish. In fact, the flower bud is pink before the corolla is unfurled. The floral tube is hidden by a light green, cylindrical calyx with parallel veins and five terminal, red-edged lobes.
From the center of the flower, fused to the floral tube (adnate), arises a fuchsia-colored contraption that looks like a bottle scrubber. This is a family characteristic of Malvaceae, the mallow or cotton family. The filaments are fused (connate) into a staminal column, adorned with about 100 stamens. Through the staminal column grows the style, which emerges at the top bearing five stigma lobes. In Hibiscus, the stigma lobes look like fuzzy red balls. Two other noticeable features include five brownish leaflike structures at the base of each flower (involucral bracts), and, on the underside of the petals, visible with the aid of a hand lens, very short, scattered, rose-colored hairs.
The ovary looks like Devil's Tower in Wyoming, albeit a miniaturized, light-green version covered with upward-pointing, rose-colored hairs. It matures, when properly pollinated, into a capsule that splits open to reveal seeds in five chambers.
If you are fortunate enough to have a very high-powered lens, you may be able to detect minute reddish-brown structures slightly recessed on the upper and lower sides of the leaf. These appear to be glands, probably producing a chemical the same as or similar to gossypol, which occurs in cotton (Gossypium). Gossypol is a plant defense against herbivory, because it interferes with animal protein digestion. Without further research, all this is speculative, but certainly you should not eat these leaves. Nor would you at MEMBG, not only because you should not damage the plants but also because our plants have been attacked by the giant white fly that has invaded Southern California. Instead, come to the botanical garden to admire the flowers of this endemic Hawaiian plant.
ARTHUR C. GIBSON, MEMBG Director