The Flowering Plants of Hawaii
Part 7 Betulaceae - Bignoniaceae - Bixaceae - Boraginaceae - Brassicaceae - Buddleiaceae
Members of Betulaceae are familiar components of northern temperate forests. Six genera comprise the family: Alnus (alder), Betula (birch), Carpinus (hornbean), Corylus (hazel or filbert), Ostrya (hop hornbean), and Ostryopsis. There are no endemic members of Betulaceae in the Hawaiian Islands. However, Alnus nepalensis (image) was one of many tree species introduced by state foresters over the years—we’ll meet others later. Although this species was planted on all of the main islands, the largest number of seedlings, ca. 1,500, were planted on Moloka`i. In 1982 it was observed that trees were spreading into the Nature Conservancy’s Kamakou Preserve. Although authors of the Manual did not include this family in the flora in a formal sense, they did note that this tree may have the potential of becoming naturalized. There was no further comment in the Addendum as to this tree’s status. One of the Nature Conservancy’s staff remarked to me that this is one of the trees that “snuck under the wire” and will have to be watched to see if it becomes a problem.
The specimen in photograph was seen beside the Kamakou access road.
The Hawaiian Islands do not have any native members of Bignoniaceae but are graced by four naturalized species representing four genera two of which are particularly noticeable on the islands. The familiar jacaranda, Jacaranda mimosifolia (see image), where the specific epithet tells us that its leaves resemble those of mimosa, is a favorite decorative species in the islands and may be familiar to many readers. The pictured tree graces one of the visitor stops on the tour of the National Tropical Botanical Garden.
Likely less well known, at least to first time visitors, is one of the most spectacular members of Bignoniaceae in the islands, or possibly anywhere for that matter. The African tulip tree, flame of the forest, or Nandi flame is Spathodea campanulata. This is the only species in this tropical African genus.
One look at the magnificent display of orange-red flowers, as seen in the illustrations readily explains why this tree has been widely planted. This species is not as aggressively weedy in the sense that we will see in many alien species, but it does move into abandoned agricultural fields and can, with seeds that germinate quickly, become a significant intruder. Tulip tree out-competes native species because of its more efficient use of available water. Thus, in draught or near-draught times this difference provides a clear selective advantage to the flame tree. Superior water use is also characteristic of other alien species, e.g., Grevillea, the silk oak (see Proteaceae).
The only member of the South American genus Bixa (Bixaceae) in the Hawaiian Islands is Bixa orellana, commonly known in English as the lipstick tree in reference to is bright orange-red fruits. Other names include annatto, achiote, and, in Hawaiian, `alaea, `alaea lä`au, or kümauna. This visitor has been on the islands since at least the mid-1860s and can be found on most islands. Its attractive flowers can be seen in the image. Bixaceae are a small tropical family with its 21 species arrayed in four genera (Mabberley, p. 107). Other than Bixa, readers may be familiar with Cochlospermum which comprises among others, C. religiosum (C. gossypium), the silk-cotton tree of Burma and India (Mabberley, p. 198).
The family of the common garden borage, Boraginaceae, is represented in the islands by a number of common invasive weeds as well as by several more noteworthy species. Among the latter is Cordia subcordata (see image), known in Hawaiian as kou. The specimen photographed here is growing in the Maui Nui Botanical Garden. A good specimen can also be seen in the garden in the Inter-Island terminal of the Honolulu International Airport—it is the tree that one sees immediately at the stairway leading to the garden. Seeds of kou were brought to the islands by the Polynesian colonists, but there is evidence from an archaeological exploration of a sinkhole on Kaua`i that Cordia was present on the island some 5,000 years before the present which predates arrival of the Polynesians (Burney et al., 2001; Burney 2010). Polynesians used the wood to fashion bowls and other utensils. The wood is more easily worked than koa (Acacia koa, which we will meet below), is very attractive, and does not impart a flavor of its own to food. The large orange flower was used for lei, and the seeds can be eaten.
In their book on woodworking on the islands, T. D. Shafto and L. Mc Daniel (2009) state, “Although it was once common throughout the islands, an introduced moth killed the majority of the kou trees in the late 1800s and early 1900s, at which time the dead or dying wood was harvested for use in furniture. Fortunately, it’s making a comeback.”
One of the most attractive of the indigenous species that one is likely to find on the islands — if, that is, one visits a sandy headland that hasn’t been covered by hotels and the like—is hinahina kü kahakai (sometimes just called hinahina), Heliotropium anomalum var. argenteum (see image). The species is widespread in the Pacific Basin; the variety is uniquely Hawaiian, however. The plants in the photograph were found growing on the coastal dunes on the north coast of Moloka`i. The flower heads are used by ladies to make hat leis. A related species, also widespread in the Pacific Basin and present in suitable dry seaside habitats on all of the Hawaiian Islands is H. curassavicum (see image) which is known as kïpükai or lau po`opo`ohina in Hawaiian.
A very commonly planted small tree, now naturalized in the islands, is Tournefortia argentea (see image), the tree heliotrope. It is common on beaches on all of the islands (except Kaho`olawe) including the northwestern Islands as far as Midway and Kure. It is native to tropical Asia, Madagascar, tropical Australia and Polynesia. In earlier literature this plant was included in the genus Messerschmidia.
Members of the mustard family Brassicaceae (or Cruciferae), much used as foods, e.g., black mustard and various cresses, are common escapes from cultivation. The Hawaiian Islands are home, however, to two endemic species of Lepidium, one on O`ahu, L. arbuscula, and one on Kaua`i, L. serra; both are rare. An indigenous species, L. bidentatum (see image) illustrated here, occurs widely in the Pacific. Hawaiian names for this plant are `änaunau, `änounou, künänä, and naunau. To varieties have been described, var. remyi from an unidentified site on the Big Island (now extinct); and var. o-waihiensis, which occurs widely on the Hawaiian Islands and other islands in the Pacific. The specific epithet for this variety is taken from an early name for the Big Island, O-Waihi, as used by Sir W. J. Hooker in commenting on the visit to the islands by Archibald Menzies. Hooker’s spelling of Maui in his comments was “Mauwi.” Standard spelling of the islands was some years away.
Two naturalized species of Buddleia occur on the islands; B. madagascariensis and B. asiatica. Buddleia asiatica is the more common of the two occurring in a wide variety of disturbed habitats as well as on lava and cinder beds. It is common along the Saddle Road on the Big Island at middle elevations, and I have seen individuals growing in a variety of places including the floor of Kilauea Iki. The Hawaiian name for this plant is huelo `ïlio, literally, tail of the dog, based upon the appearance of the flowering head (see image). A mature plant with a prolific crop of seeds is shown in the last image. A common decorative plant in my home area, southwestern British Columbia, is B. variabilis, commonly called butterfly bush. This plant has escaped from cultivation and is slowly making its way to higher elevations along road cuts.
Some authorities include Buddleia in Loganiaceae (noted in the Manual) or Scrophulariaceae (Soltis et al., 2005; Mabberley, p.127). Authors of the Manual recognize Buddleiaceae in its own right and we follow that usage here. Some sources have Buddlejaceae as the preferred spelling. As noted elsewhere in this series, some family associations will change as the result of comprehensive research based on DNA sequence data.
December 12, 2011