The Flowering Plants of Hawaii
Part 23 Lamiaceae (Labiatae)
Lamiaceae (Labiatae), the mint family, are a large, nearly cosmopolitan family of 238 genera and 6,500 species (Mabberley, p. 460-461). The family is home to many familiar plants used in medicine, as flavoring agents in cooking and confections, and aromatic preparations for soaps and other cosmetic products. Many of the cooking herbs, such as the mints themselves (Mentha species), basil, oregano, rosemary, thyme, lavender, and many others, have been cultivated for centuries and have escaped from gardens wherever they have been grown. The Hawaiian Islands are no exception where one finds mints, basil, sage, and horehound growing successfully. Several family members are common weeds including Leonurus sibiricus (see image), known as lion’s tail; and the common Prunella vulgaris. A widespread weedy species is the attractive Salvia coccinea, lililehua in Hawaiian or scarlet sage (see image) in English.
The most noteworthy members of the family on the islands, however, are the two endemic genera Haplostachys with five species and Stenogyne with 20, and Phyllostegia which has 27 species in the Hawaiian Islands and a single outlier in Tahiti (P. tahitiensis). Haplostachys is a genus that seems nearly to have run its course. Of the five listed species, four are marked in the Manual as extinct, and the sole surviving one, H. haplostachya, honohono in Hawaiian, is presently only known from a single site, Kïpuka Kalälawamauna, on the Big Island. This site lies on the western side of the Saddle. Collection data tell us, however, that this species occurred on Maui and on Kaua`i, and at other sites on the Big Island. This species is being maintained in cultivation; I have seen it in the glasshouse collections at the NTBG, and at the Rare Plant Nursery at Volcano. It is a very beautiful plant as can be seen in the figure (see image). Authors of the Manual suggest that members of Haplostachys were rare even at the time of first contact with European botanists (Cook’s visit). As a result, little is known about the biology of any of its members, with the exception of the lone survivor. A few details on the remaining species may give a better perspective on rarity. Haplostachys bryanii, last collected in 1918, occurred in dry areas of southwestern Moloka`i. It was replaced throughout its range by pineapple plantations. Haplostachys linearifolia occurred at one time on Maui and on Moloka`i. It was last collected on the latter island in 1928. It was also a plant of dry shrub and woodland, ideal for agricultural purposes, after removal of the native vegetation, of course. Haplostachys munroi occurred in dry sites on the western end of Läna`i and was last seen there in 1935. Recently, a few individuals were rediscovered in dry forest in western Läna`i. I was fortunate to see one of the plants during my visit to the island in early 2009; unfortunately, I failed to get a useful image of the specimen. Haplostachys truncata is known only from the type specimens collected on Maui during the period 1851-1855 by Ezechiel Jules Rémy.
Rémy was a French naturalist and ethnologist who visited the Hawaiian Islands during extended trips around the world between 1851 and 1863 (Manual, p. 120). Some early collectors were guilty of the annoying habit of marking all of their specimens with the date of their visit—in this case to the Hawaiian Islands which Rémy visited twice. Thus, we know only that the plant used to grow on Maui and was collected to extinction by Rémy on or after July 1, 1854. It is not uncommon to find species described in the literature as “known only from the type.” Having found an organism that was unknown to the collector—and, at that time, presumably to the rest of the botanical community—many specimens were collected for deposit in his (rarely her, this is not sexism, it’s history) home herbarium, or the herbarium of the organization underwriting the journey. Not knowing anything about the native range of the new find, collectors frequently turned to their task with considerable enthusiasm and collected all specimens in sight. With limited time available to them, a wider search in similar habitats for additional populations was not an option. So, without knowing what they were really about to do, they brought a newly discovered organism to the attention of science, and to the brink of extinction at the same time.
The situation with regard to Phyllostegia, with 27 species in the Hawaiian Islands and one in Tahiti, is not quite as dire as we just saw with Haplostachys. Of the 27 Hawaiian species of Phyllostegia, five are extinct: P. brevilens is known from only two collections, both made prior to 1871; P. hillebrandii is known from collections made prior to 1871 as well; P. imminuta was last seen on Läna`i and East Maui in 1928; P. rockii is only known from three early collections on Maui; and P. variabilis, last seen in nature in 1961, occurred on Midway and Kure atolls and on Laysan. Natural sites on these three islands have been massively compromised through human activity. A dozen species of Phyllostegia, and a variety of another, are listed as rare or endangered, and some of these might well be gone were the original sites visited again today. That leaves ten species represented in nature by enough individuals to suggest that they may have a reasonable future. I have the staff at the Hawaiian Rare Plant nursery at Volcano to thank for allowing me access to their Phyllostegia specimens, photographs of which follow. Phyllostegia warshaueri (see image), one of the rarer species, is a native of wet forest on northeastern slopes of the Big Island. Two species that appear to be in no immediate harm are P. vestita (see image), and the very attractive P. floribunda (see image) both of which are native to forests on the windward side of the Big Island.
The third genus in this triad is Stenogyne with 20 species. Of the three genera, Stenogyne, with only four extinct species and five listed as rare, is in the best shape. Tales of the extinct species read very much as we saw for the examples above: S. cinera was collected once on East Maui in 1865; S. haleakalae, native to the southern slopes of Haleakalä, was last seen in 1936; S. oxygona was last seen in the Kohala Mountains, Hawai`i in 1952 (possibly still extant, but obviously rare); and S. viridis Which was collected only once by Hillebrand (late 19th century). Two of the rare species deserve some comment as well. Stenogyne kanehoana was described in the Manual as consisting of a single population of three or four plants in the Wai`anae Mountains (O`ahu). Since that information is at least 10 years old, it is possible that this species may be on—or approaching membership in—the list of species driven to the brink of extinction through invasion of alien species. The second example, Stenogyne campanulata, was first described in 1986 from collections made on a cliff above Kalalau Valley (North coast of Kaua`i). I have been unable to obtain a photograph of this species but a view of the northwest-facing cliff in the valley is included here to give the reader an idea of the sort of terrain we are talking about (see image). The Pihea Trail, referred to here and elsewhere in this series, skirts the Kalalau Valley on its southern rim. Without assistance—a well-rooted tree and a colleague with a strong rope—collections over the rim of the valley would be a life threatening adventure. Even with those provisions collecting in this kind of terrain can be very exciting!
During my various visits to the islands I have been fortunate to find a number of Stenogyne species in their native habitats. One of the prettiest of these is S. calaminthoides (see image), whose pink to red flowers stand out brilliantly against the green understory vegetation. Its leaves, on trailing vines, are characteristically shaped and are a dark, shiny green—enhanced by the almost constant mist, drizzle, rain, or downpour to which they are exposed. The photograph was taken along the service road in the vicinity of the Thurston Lava Tube in Hawai`i Volcanoes National Park. At higher elevations and in drier terrain an alert visitor can find S. microphylla (see image). This species, which frequently grows intertwined with mamane (Sophora chrysophylla), can be seen in the vicinity of Hale Pohaku, the mid-mountain astronomy center on Mauna Kea at about 9,200’ (ca. 2,800 m) elevation. This species is easy to identify by its small, purple flowers and its sharply right-angled branching patterns. A return visit to the area in 2011 failed to yield more than a single living individual of S. microphylla likely the result of the prolonged drought that has plagued the area over the past several years. Several other one-time common elements of the flora were also conspicuous by their absence, e.g., geraniums.
Keen eyed visitors hiking along the boardwalk portion of the Pihea Trail on Kaua`i might be fortunate to see the pinkish-purple flowers of the Kaua`i endemic S. purpurea (see image) among trailside vegetation. The Boy Scout trail in the Waihe`e area of East Maui offers a short, steep but rewarding hike along a ridge with attractive vistas on both sides. Near the top of the trail it is possible to find the vine S. kamehamehae (see image), adorned by its large and attractive cream to pink flowers, snaking through the undergrowth. A darker pigmented form occurs in the vicinity of the alpine meadow on Moloka`i and other sufficiently wet sites. On three visits to the Moloka`i site the plant failed to reveal itself to me. While crawling about in the low vegetation of the area, however, I did chance upon very nice specimens of one of the islands’ endemic violets, which we will meet in a later part of this series.
The origin of the endemic Hawaiian mints has attracted a good deal of attention. The family has such a wide distribution worldwide that colonization of the Hawaiian Islands could conceivably have come from any one of several sources. The problem was addressed experimentally by Charlotte Lindqvist and Victor Albert, of the Natural History Museums and Botanical Garden of the University of Oslo, using chloroplast and nuclear gene sequence data. Preliminary studies had identified a number of North American members of Stachys as particularly close to the Hawaiian genera. Their results, published in 2002, demonstrated clearly that: (1) the three genera are very closely related to each other; (2) their nearest mainland relatives are a group of Stachys species from the Pacific states (species akin to Stachys quercetorum and S. chamissonis); and that a single colonizing event can explain their presence on the islands. Furthermore, it is possible to estimate a time period during which such a colonizing event would have occurred based upon changes in the DNA sequences studied. Although a seemingly very wide range emerges, 2.6-7.4 million years ago, it is within the range of times estimated for the silverswords, 5.2 million years, and for the lobelioids, 8.7-17.4 million years ago. A key point in all of these discussions is the knowledge that at least one high island existed during those periods to serve as a landing place.
Before leaving the islands’ mints, it is useful to take a brief look at some of the diversification that has occurred during their time on the islands: just what sorts of things developed over the several million years since the colonist first arrived? We have already seen that the 60 or so species occupy a wide array of habitats—from drier (Haplostachys) to rainy and very rainy (Phyllostegia and Stenogyne)—and occur over an equally wide range of elevations. This process—the occupying of available ecological niches, technically, adaptive radiation—has been found to occur in every group of Hawaiian species studied. In addition to habitat specialization, essential biological processes, reproductive strategies for example, also show significant diversification. The flowers of Stenogyne have red-pink pigmentation, reduced lower lips and more elongated floral tubes, are odorless, and produce abundant nectar, features associated with bird pollination. Species of Haplostachys and Phyllostegia, in contrast, have fragrant, pale colored flowers with prominent lower lips, features associated with insect pollination. Fruit types differ as well; Haplostachys produces dry fruits, whereas those of Phyllostegia and Stenogyne are fleshy.