The Flowering Plants of Hawaii
Part 49 Urticaceae - Valerianaceae - Verbenaceae
The Urticaceae would be well known to anyone unfortunate to have encountered stinging nettle. The common stinging nettle is Urtica dioica, a Eurasian plant now widely naturalized, including in North America. On the Island of Hawai`i one might encounter one of its relatives, U. urens, the dwarf, burning, or dog nettle. This is a stinging nettle as its common name attests. It is interesting to note that members of the family that are endemic to the Hawaiian Islands, however, do not have stinging hairs. Other genera of urticaceous plants on the islands are Boehmeria with one endemic species; Hesperocnide, a genus of two species, one endemic in the islands and one in California; Neraudia, an endemic genus with five species most of which are listed as rare; Pilea with one naturalized and one indigenous species; Pipturus, with four endemic species; and Touchardia, an endemic monotypic genus.
Boehmeria grandis (see image), `äkölea in Hawaiian, the sole member of this pantropical genus in the Hawaiian Islands, can be found growing along streambeds, moist valleys, and in a variety of forest settings on all of the main islands except Ni`ihau and Kaho`olawe. Members of this genus, as is the case with other island natives, do not have stinging hairs, thus one of the common names, false nettles. One of the species, B. nivea, is cultivated for its long fibers favored for their silkiness (Mabberley, p. 110). Extraction and cleaning of the fibers, however, is difficult; commercial production of this product was attempted but was never successful in the Hawaiian Islands.
Hesperocnide, a genus of two species, is represented in the islands by H. sandwicensis (see image), a rare endemic plant that finds its home at middle to higher elevations between Mauna Kea, Mauna Loa, and Hualälai. The other is H. tenella, a native of California. Authors of the Manual quote Hillebrand’s 1888 suggestion that the island species might have arisen from plants brought to Hawai`i when Capt. Vancouver introduced cattle. Differentiation would have produced the present species, obviously closely related to, but clearly different from the mainland plants. It would be of interest to determine the level of genetic differentiation that has occurred, which would be expected to be very small, if even detectable, owing to the short time of residence on the islands.
The Hawaiian endemic genus Neraudia consists of five species. The example we have here is N. melastomifolia (see image). This is the most common of the species with principal centers of variation on Kauai and O`ahu with scattered reports from other islands. It is known as ma`aloa, ma`oloa, or `oloa in Hawaiian.
The genus Pipturus, known as mämaki or mämake in Hawaiian, consists of 30 species distributed from the Mascarene Islands to Polynesia (Mabberley, p. 672). It is represented on the Hawaiian Islands by four species. The representatives shown here are P. alba (see image), which occurs widely in the islands, and P. kauaiensis (see image), which is endemic to Kaua`i. Several specimens of this plant can be seen at Limahuli Garden in the area devoted to regeneration of the mixed forest. The inner bark of Pipturus provided strong fibers useful as cordage and for making a kind of tapa cloth.
Touchardia latifolia (see image), olonä in Hawaiian, is the sole member of this endemic Hawaiian genus. This shrubby species, which occurs on all of the main islands except Ni`ihau and Kaho`olawe, was used by the early Polynesian colonists as a source of strong fiber. In addition to the various uses by the islanders, including the weaving of fish nets, early seafarers bought quantities of rope made from the fibers for ships’ rigging. Not only were the ropes stronger than the hemp ropes normally used, but they did not kink and they were highly resistant to sea water. Olonä is one of the few native Hawaiian plants for which early colonists found a use.
The last representative from the family is Urera glabra (see image). This species, known as öpuhe, höpue, or hona in Hawaiian is one of two that occur on the islands; both are endemic and are likely to have been the result of separate introductions according to authors of the Manual. The other 40 or so species (35 according to Mabberley, p. 887) occur spread between South Africa, Madagascar, and tropical America. Hawaiians used this plant as a source of fibers for fish nets and as a base for fashioning feather cloaks.
The sole member of Valerianaceae on the islands is Centranthus ruber, a Mediterranean species grown as an ornamental. This attractive plant exhibits different flower colors as seen in the illustration (see image).
Verbenaceae, as viewed by the authors of the Manual, consist of some 100 genera and perhaps 2,600 species. Recent analysis of DNA sequence data resulted in transfer of several of the traditionally included genera to several other families including the Lamiaceae (Soltis et al., 2005). Two of the genera that we will look at here, Lantana and Stachytarpheta, remain in the new, trimmed down Verbenaceae, which Mabberley lists as comprising 1,150 species in 35 genera. Clerodendrum and Vitex have been moved to Lamiaceae (Labiatae) but we will consider them here in the older context of Verbenaceae.
Lantana, a genus of 150 species from tropical America and tropical and South Africa, is represented in the Hawaiian Islands by two species, L. montevidensis, which has become naturalized in abandoned pineapple fields on Läna`i; and L. camara (see image), läkana (Hawaiian pronunciation of the genus name), which is one of the more virulent aliens which can be found on all eight of the main islands. This multicolored flowerd (see image), attractive to butterflies, and the ease of cultivation make this shrub of value to some gardeners. The plant is unpalatable to stock and can spread quickly through pasture land. Physical removal, as in the case of all major weedy species in the islands, is labor intensive, and use of herbicides carries with it the same risk as their use against other alien species. The use of biological control agents against weeds in the islands was mentioned above, e.g. thrips against miconia, the fungus Colleotrichum against Koster’s curse, and a scale insect against strawberry guava. It was in response to the rapid spread of Lantana toward the end of the 19th century, however, that biological control agents were first employed in the islands.
Lantana was introduced into the Hawaiian Islands in 1858 but did not immediately become a problem; that had to wait for the appearance of another alien. In 1865 the common mynah bird (Acridotheres tristis) was introduced into the islands to control armyworms, the larval form of noctuid moths. The problem arose when the mynahs became the carrier of lantana fruits. The presence of lantana on the Big Island was commented upon by Isabella Bird, whose comments on silverswords we met in Chapter Two. She was particularly taken with Hilo, its surroundings, and the people she befriended there. Her feelings went further as shown by comments she recorded in her diary on May 24 describing her ride (on horseback) from Laupähoehoe to Hilo: “…and indeed each tree, flower, and fern in Hilo is a friend. I would not even wish the struggling Pride of India (Melia azedarach, author’s note), and overabundant lantana, away from this fairest of the island Edens.” Of particular interest in the present context is her description of lantana as “overabundant,” and that was in 1873! She also described seeing many places, “…where the hill slopes are now only a wilderness of guava shrub…” It is likely that Ms. Bird was describing Psidium cattleianum, the strawberry guava, which had been brought to the islands as part of the botanical cargo of HMS Blonde in 1825.
The first release of a potential biocontrol agent occurred in 1902 after a search for natural enemies of lantana in its native Mexico was carried out by Albert Koebele, an entomologist associated with the Commission of Agriculture of the Provisional Hawaiian Government. This was just the first of many insects imported into the islands to combat invasive weeds. In many of these cases studies to determine species specificity of the ‘attack’ insect were not carried out. It is interesting to note that present day importation of insects involves a long stay in quarantine until species specificity (or high selectivity) and absence of contaminating organisms—microorganisms infecting the insect—have been established. In contrast to the catch, transport, and release approach practiced in earlier times, the present protocol can require up to 10 years before release is authorized. The history of the use of biocontrol agents in the islands and lessons learned are reviewed in detail in papers by Davis et al. (1989) and Markin et al. (1989). The overall conclusion on the early studies is that biocontrol has worked well on lantana.
Another biological control agent that has been effective against lantana is a species of the ascomycete genus Septoria which was introduced from Ecuador in 1984 (Trujillo, 2005). Sites inoculated with fungal spore suspensions between 1989 and 1999 are showing significant decline in lantana. Continuing decline in populations in the Koke`e area, first inoculated in 1996, were observed in early 2009 (Trujillo, personal communication).
Gardeners may not recognize the fungus Septoria by its scientific name but are almost certainly familiar with the symptoms of infections by members of the genus. Various species are responsible for leaf-spot diseases on many field crops as well as vegetables.
Stachytarpheta is a genus of about 90 species from the New World with a few in southern Africa. The Hawaiian Islands have four species all of which are easily identified to genus by their characteristic long spike of blue to purple flowers. Stachytarpheta urticifolia (see image) is widely distributed in shaded, mesic, disturbed habitats. The photograph was taken near the trail to Hanakäpï`ai Beach, northwestern Kaua`i.
Clerodendrum philippinum (see image), pïkake hohono in Hawaiian, is a species that occurs in mesic to wet sites including stream banks and taro patches. The photograph of this species was taken near the extensive taro fields in the Hänalei Valley, northern Kaua`i. The Hawaiian name is derived through combination of pïkake, which is a sweet smelling species of Jasminium, and hohono, a word meaning bad smelling. Evidently, the aroma of Clerodendrum is less pleasing than that of pïkake, at least to some people. The horticultural literature suggests that this species is grown for its pleasant aroma; tastes differ one presumes. Whereas C. philippinum is the currently accepted name for this plant, it was at one time called C. fragrans, a name based upon its attractive aroma. On O`ahu this plant is called pïkake wauke; wauke is the paper mulberry (Broussonetia papyrifera) whose large leaves resemble those of Clerodendrum. According to the Manual, and other horticultural sources, this species reproduces solely by root suckers, which appears to be an efficient way of enlarging one’s garden collection. The downside of this capacity is that, untended, this plant can become an invasive nuisance.
Some may well ask how a plant that does not produce seeds and reproduces solely by root suckering could find its way into a natural setting. If one has ever witnessed someone dumping lawn cuttings or garden waste onto an unused lot or beside a road, then you have the answer. Bits of Clerodendrum root material dumped in a roadside ditch, almost certainly full of water or at least damp, would quickly take root. Bits of plant material lodged in tire treads can also be transported significant distances from source.
The last example in this section is the indigenous Vitex rotundifolia (see images), known as beach vitex in English, and, among others, kolokolo kahakai in Hawaiian. Kolokolo refers to any creeping vine; kahakai identifies this creeper as growing near the ocean. Beach vitex occurs over a wide area from China, Taiwan and Japan, south to India and Sri Lanka, as far west as Mauritius, through Malesia, Australia, and the Pacific Islands. The widespread beach habitat suggests that this species is readily spread by flotation, or by shore birds. Because of its capacity to grow rapidly and root at nods this species has been used as a beach stabilizer.