The Flowering Plants of Hawaii
Part 4 Aquifoliaceae - Araliaceae - Aristolochiaceae - Asclepiadaceae
Aquifoliaceae, the holly familalay, is represented on the islands by the genus Ilex with three species, two that have escaped from cultivation and one that is indigenous (although at one place in their discussion, the authors of the Manual say that it is endemic). The Hawaiian species, I. anomala, also occurs in Tahiti and the Marquesas. The Hawaiian name for this plant is kawa`u except on Kaua`i where it is called `aiea. It can be found on all of the main islands growing in mesic to wet forests; it does not occur on Ni`ihau or Kaho`olawe, both of which are too dry. Some of the best specimens that I have seen, and the one whose photograph appears here, are easily found in the vicinity of the Thurston Lava Tube (Nahuku in Hawaiian), Hawai`i Volcanoes National Park, along the trail that leads from the Lava Tube parking lot to the Kilauea Iki Overlook parking lot, and along the Pihea Trail on Kaua`i. Hawaiians used the wood for a variety of things including trimming for canoes and as an anvil for kapa (tapa cloth) beating.
The two naturalized species of Ilex on the islands, although not nearly as widely spread, are I. aquifolium, the English or European holly, which occurs in a ranching area on Mauna Kea; and I. paraguariensis, yerba maté, or Paraguay tea, which now grows on O`ahu. How widespread these two will become remains to be seen: English holly was first reported as a naturalized species in 1987, while yerba maté has been ‘on its own’ since 1934.
Estimates of the number of species in Ilex range from 400 to about 500 depending upon taxonomic opinion. Relationships among groups of species within this nearly cosmopolitan genus were studied by the Swiss botanist Philippe Cuénoud and colleagues (2000) using chloroplast gene sequences. Specimens of I. anomala from the Hawaiian Islands were included in their study of 115 species representing the entire range of the genus. The data indicated that the Hawaiian/Tahitian species is most closely related to North American species, but no candidate was named as the most likely ancestor.
Although it is not present on the Hawaiian Islands, the genus most likely known to most readers from Araliaceae would be Ginseng. Another would be Hedera helix, English ivy, which has been cultivated since the early 1900s and is naturalized on the islands. A third species that has been cultivated on the islands and is now naturalized in disturbed areas, mostly at lower elevations is the octopus tree, Schefflera actinophylla. This tree, which can attain heights of 15m (ca. 50 ft), is easily recognized by its palmately compound leaves (like a palm with fingers) and distinctive arrays of pink-red flowers (see image) . A particularly large specimen stands in a yard adjacent to Highway 270 in the North Kohala area of the Big Island. Immediately across the highway on the grounds of the Kohala Information Center in Kapa`au visitors can find the original statue of Kamehameha I (Kamehameha the Great), whose birthplace is nearby. For visitors on Kaua`i, octopus trees can be seen in bloom in early May in the vicinity of the Plantation Marketplace and nearby hotels in the Kapa`a area.
Our next visit is to the Polynesian genus Cheirodendron. Five of the six species in the genus are endemic on the Hawaiian Islands, with the sixth native to the Marquesas. One of the species, C. dominii, found only on the summit of Mt. Wai`ale`ale on Kaua`i, is the only Hawaiian species marked as rare; the rest are fairly easy to find in Nature. A convenient, and very attractive, place to see C. platyphyllum subsp. kauaiense (see photo) is along the Pihea Trail in the vicinity of the Kalalau Valley lookout. The trees line the forest side of the trail. The other subspecies, C. platyphyllum subsp. platyphyllum, occurs on O`ahu. This, and other, species of Cheirodendron are called `ölapa or lapalapa in Hawaiian, owing to the slapping sound the leaflets make in a breeze, a phenomenon much akin to the effect of wind blowing through a thicket of trembling aspen. Cheirodendron trigynum (see photo) occurs on all of the main islands in mesic to wet forests. The plant pictured in the plate was found growing along the power line access road that parallels the Saddle Road on the Big Island. This track is accessible via a turnoff from the Saddle Road near mile19 and provides a comfortable access to mid elevation scrub forest. Two subspecies are recognized, subsp. helleri which grows only on Kaua`i, and subsp. trigynum, which is the more common form and the one featured here.
A characteristic feature of these species, and others in the genus, is their compound leaves with, usually, three leaflets: in C. trigynum the central leaflet is the largest of the three, whereas In C. platyphyllum the leaflets tend to be broader than long. Cheirodendron fauriei (not shown), a Kaua`i endemic, has toothed leaves and is locally common in the Koke`e area and in places along the Power Line Trail. All tend to have quite shiny leaves.
The Hawaiian flora has recently experienced a loss of two endemic genera from the family, Munroidendron and Tetraplasandra, and a third, Reynoldsia, that was represented on the islands by an endemic species. Fortunately, the losses were the result of a comprehensive investigation of the related genus Polyscias and not extinction in the biological sense. Current plant systematic work requires that generic names of organisms reflect their evolutionary relationships, which are based to a very significant degree upon DNA sequence data. Family realignments may also be necessary. We see both of these outcomes in this examination of the Hawaiian flora. This continues to perplex some folks who see familiar plants being called something totally alien (in their view), and even more upsetting see them removed from their traditional family alignments. In the present instance we see the loss of three familiar names, but no change in family status.
The new home for Munroidendron, Reynoldsia and Tetraplasandra is the much larger genus Polyscias, which consists of at least 100 species (Mabberley, p. 691), with representatives in Madagascar, the Mascarene Archipelago (Mauritius, the Seychelles, Réunion, Rodrigues, and others), New Guinea, New Caledonia, and, as a result of recent studies, islands in the Pacific including the Hawaiian Islands. As pointed out by the authors of the relevant studies (Plunkett and Lowry II, 2010; Lowry II and Plunkett, 2010), the number of genera in the Araliaceae has been a matter of discussion for some years with the number ranging from about 40 to 85, and that Polyscias, the largest genus in the family, was not a natural group, that is to say that all members of the genus as formerly constituted did not share a common ancestor. In order to bring some order to this disparate arrangement, and to identify evolutionary relationships within this large group of organisms, these workers employed DNA sequence data on a large sampling of specimens representing the range of the genus, and potentially related groups.
One of the Hawaiian species involved in these studies is Polyscias racemosa (formerly Munroidendron racemosum), a strikingly attractive species of flowering tree endemic to the island of Kaua`i (see photos). Once thought to be extinct, this plant is known naturally from only a few locations on Kaua`i, none of which is easy to visit. it is maintained very successfully in cultivation in several gardens, however, including the Limahuli Garden and the NTBG. Plants were originally described as belonging to Tetraplasandra but subsequent analysis led to description of a new genus, Munroidendron, in 1952. Authors of the Manual suggested that this recognition may not be justified insofar as the features that distinguish the two genera are minimal (at the generic level, at least).
The next name change victim of the study was Reynoldsia, which was originally described to encompass six species, two in Samoa, two in the Marquesas, and one each in the Society Islands and in the Hawaiian Islands. Polyscias sandwicensis (Reynoldsia sandwicensis) occurs on Läna`i, Ni`ihau, Maui, Moloka`i, O`ahu, and the Big Island. The photograph of this species was taken on the island of Läna`i in a forest preserve dedicated to the preservation of a remnant hardwood forest, one of the rarest and most threatened forest types on the islands. A visit to Läna`i in January 2009 afforded an opportunity to meet a group of folks, `Ike `Äina, the Native Hawaiian Land Trust, dedicated to preservation of areas of natural vegetation on the island. The photograph shows the tree almost totally surrounded by the aggressive weedy Schinus terebinthifolius (the Christmas berry, Anacardiaceae), which we met above. One of the objectives of `Ike `Äina is to locate situations such as this and remove the offending alien plants so that seedlings of the native species have a chance to survive. Fencing is also necessary to keep feral animals from eating seedlings and having further negative impact on the plant’s habitat. This species, as is the case with most native species, rebounds well once its native habitat has been cleared of invasive alien plants and protected from feral animals.
Hawaiians have several names for P. (Reynoldsia) sandwicensis including `ohe, `ohe makai, `oheokai, `ohe kukuluae`o, and, on Ni`ihau, `ohe`ohe. It is instructive to pause here for a moment to appreciate the meanings of these words, some of which take one into realms quite distant from the normal experience of field botanists (Pukui and Elbert, p. 178). First, and simplest, is `ohe, the general term for Reynoldsia. The second and third terms tell the reader something about where the tree lives, ‘toward’ the sea in the case of `ohe makai, and ‘of the sea,’ implying coast, in the case of `oheokai. Things get a little more complex, and intriguing, when the word kukuluae`o enters the scene. Kukuluae`o is the word for stilts, or to walk on stilts (some Hawaiian words can be a noun or a verb) referring to the use of its limbs to make stilts
It appears that things were a little different on Moloka`i, and specifically on Maunaloa (the older of the two main volcanoes on that island), where sinister things were brewing, or rather being carved. Wood of trees growing on that end of the island was thought to be poisonous, and from it were fashioned poison images. I have found no information regarding this property in plants from the other islands. It would be interesting to identify toxic compounds that might occur in the wood, and see if this feature is unique to plants from Moloka`i or whether it might be a more widespread phenomenon or simply a tale whose origin is lost in Hawaiian history. As a comparative plant biochemist—someone who looks at similarities and differences in the chemical components of supposedly related plant species—I was immediately drawn to the possibility that there may be chemical differences between the members of this genus from Moloka`i and those from the other islands; such variation is in no way unusual (Bohm, 2009). It is not unusual for local peoples to recognize these differences, and to make use of them.
The largest group of species to be affected by the name change constituted the genus Tetraplasandra. Polyscias (Tetraplasandra) gymnocarpa, endemic on O`ahu, is the only member of the genus that is listed as rare or endangered; its numbers have decreased to the point that it is presently restricted to the summit of the Ko`olau Mountains (the eastern range on O`ahu). The most common member of this genus on Kaua`i is P. kaviensis (see photo), known as `ohe`ohe. This specimen was photographed along the Nature Trail at the Koke`e Museum. It also occurs on the other main islands, except Moloka`i. Polyscias oahuense (see photo), here seen growing along the Waihe`e Ridge Trail on Maui (also called the Boy Scout Trail), occurs on all of the main islands except Ni`ihau and Kaho`olawe. Hawaiians obviously saw similarities between Tetraplasandra and Reynoldsia since the name `ohe, or `ohe`ohe, or some form of `ohe is common. The Hawaiian name for P. (T.) oahuense is `ohe mauka, which means an `ohe towards (or on) the mountains. In giving directions in the islands one frequently hears ‘mauka’ when referring to some location up a mountain. Conversely, makai means towards the sea.
A study of relationships within this group of three genera by Annemarie Costello, of the Ross School, and Timothy Motley of Old Dominion University, was described in 2007. These workers used a combination of morphological features and DNA sequence data to address two questions: (1) Do these three genera constitute a monophyletic group, that is to say, are they all derived from a common ancestor?; and (2) Are Tetraplasandra and Reynoldsia monophyletic? The first question was answered strongly in the affirmative supporting the view that they are indeed a closely related set which has resulted from a single colonization event, with subsequent diversification. The data also supported the view that the species of Tetraplasandra constitute a closely related group. An unsuspected outcome of the analysis, however, was the emergence of Reynoldsia sandwicensis as more closely related to Munroidendron than it is to the other species of Reynoldsia. In the language used above, this means that Reynoldsia, as currently constituted, is a polyphyletic group, i.e., the species are not all derived from a common ancestor. According to the rules of phylogenetic systematics, this outcome requires rethinking the naming of these species, a situation that will be addressed below.
Another issue that arose was the possible involvement of yet another genus of araliads (a term referring to members of Araliaceae) that could play a part in the study of relationships among members of the Hawaiian Tetraplasandra group. The genus in question is Gastonia, which consists of nine species distributed in East Africa, Madagascar, the Mascarene Archipelago, Malesia, and Papua New Guinea. Three species of Gastonia were included in the Costello-Motley study (technically, as the outgroup) with interesting results. Gastonia spectabilis, a native of Papua New Guinea was sister species to a group of Hawaiian araliads consisting of Reynoldsia sandwicensis, Munroidendron, and all species of Tetraplasandra; in other words, these results suggest that Gastonia spectabilis and the entire Hawaiian assemblage share a common ancestor.
The recent publications by Plunkett and Lowry, noted above, addressed all of these issues with the outcome being a thorough reassessment of relationships among this group of genera. Their data corroborated the findings of Costello and Motley, and allowed the much broader redefinition of Polyscias to include all of the species that once comprised Munroidendron, Reynoldsia, Tetramolopium, as well as Gastonia, which had been implicated in the Costello-Motley study, and other genera not relevant to the Hawaiian flora. In the final analysis these workers recognize 159 species of Polyscias which fall into 10 subgenera, one of which, subgenus Tetraplasandra, consists of all of the Hawaiian members of Munroidendron and Tetraplasandra, all members of Reynoldsia, several historically recognized species of Polyscias, and two species of Gastonia. This is one of the largest nomenclatural rearrangements to date involving Hawaiian species. It is unlikely to be the last.
As if the intrigue and mysterious goings on with poison images isn’t enough to justify a word of its own, `ohe has a number of other definitions including a term for all kinds of bamboo, for a native species of the grass genus Isachne, for a native species of the bamboo-like plant Joinvillea, and for a variety of kalo (taro) that has the same coloration as a variety of bamboo. Although Hawaiian is a language capable of great subtleties, it does have a substantial number of words whose meanings differ significantly depending upon context.
Aristolochiaceae, the birthwort family, have a single naturalized member on the Hawaiian Islands: specimens of Aristolochia littoralis have been found in the vicinity of Pearl Harbor. Members of this family are insect trappers and are often sought after by collectors interested in exotic plants. Dutchman’s pipes—species of Aristolochia—are popular in this regard. One wonders if the plant here might be a reject, accidental or otherwise, from such a collection.
Asclepiadaceae, the milkweed family, is represented on the Hawaiian Islands by three naturalized species, two in the type genus Asclepias, and one in Stapelia, the carrion flower. Asclepias physocarpus (see photo) was photographed in disturbed grassland near the beginning of the Boy Scout Trail (Waihe`e Ridge) on Maui. This species was originally introduced to the islands as a potential fiber crop, an enterprise that did not distinguish itself in the islands’ economy. It can be found on most islands, except Ni`ihau or Moloka`i.
A visit to Oneloa (literally Long Sand) Beach in Makena State park on Maui revealed, in addition to the spectacular beach itself, and the rays with whom Lesley and daughter Liz swam, a milkweed that I had never seen before. This two-meter tall, woody shrub had masses of delicately colored flowers (see photo ) and a copious seed load (see photo). According to my reading of the identification key in the Manual, this species has not been reported on the islands.
The only member of Stapelia included in the Manual is S. gigantea (see photo) described by the authors as native to tropical and southern Africa and Mozambique. The genus consists of 47 species (Mabberley, p. 817). The plants are characterized by having photosynthetic stems either lacking or with very small leaves. Perhaps the most noteworthy feature of these plants is the lurid coloration and markings of the flower suggestive of rotting flesh with aroma to match. The combination of color and odor is attractive to carrion flies who are responsible for pollination. True to the common name Zulu-giant, S. gigantea can have flowers with diameters up to 12” (ca. 46 cm.). According to the Manual, S. gigantea has been recorded as “sparingly” naturalized at several locations on O`ahu. The specimen in the illustration was found growing among beach rocks at Kapukahelu Beach—known locally as Dixie Maru Beach—on the west coast of Moloka`i. I was informed by a local resident, who chanced by as I was photographing the plant, that she had at least one specimen in her garden. It is easy to see how this species could be dispersed through a combination of the large yield of typical milkweed seeds and wind. Authors of the Manual state that several species of Stapelia have been cultivated in the islands since the latter part of the 19th century.
DNA-based studies now place Asclepiadaceae within Apocynaceae (see Soltis et al., 2005). Newer floras will likely reflect this change.
November 16, 2011