The Flowering Plants of Hawaii
Part 8 Cactaceae - Campanulaceae
The cactus family needs little in the way of introduction to most readers. The family consists of 1,210 species arranged in 118 genera (Mabberley, p. 133-134). There are no native cacti in the Hawaiian Islands, but several species have been imported for use as decorative plants, reportedly from Acapulco, Mexico early in the 19th century. Night-blooming cereus, Hylocereus undatus (see image), is popular and has become naturalized on all of the main islands. This cactus, night-blooming cereus in English, owing to its sweet-scented blooms which open overnight, is known in Hawaiian as pänini o kapunahou, a specific name for the species, or päpiki pua. Pä is the Hawaiian word for fence, wall or corral (Pukui and Elbert, p. 296); pua is the word for plant or flower. Both päpipi and pänini can be taken to mean cattle-fence, one of the uses to which cactus plants were put in the islands. Cacti took well to the growing conditions, particularly in hot, dry areas on the islands, grew quickly, and required little in the way of maintenance.
The second species that we’ll look at here is Opuntia ficus-indica (see image). In English this plant is known as prickly pear owing to its edible fruits and as pänini or päpipi in Hawaiian. Prickly pear occurs on most of the main islands and does particularly well in warm, dry areas such as the pasture land on the western and northwestern slopes of Mt. Kahala, on the Big Island. The potential of this plant for fence duty is clearly demonstrated in the photo. The vigorous growth of new ‘paddles’ from an old stump is shown in next image.
As just noted, prickly pear was successful as a natural fencing to control cattle, but problems arose because of its rapid growth and capacity to out-compete native species. Attention turned to biological control after the plant had become a major menace on Maui. Taking the lead from Australia, where larvae of the cactus moth Cactoblastis cactorum, had been used successfully, moths were introduced into the Hawaiian Islands in 1950. Excellent results have been obtained, including removal of an infestation of the cactus from the Hawai`i Volcanoes National Park in 1985.
Close inspection of plants, such as in the pastures mentioned above, reveals that most of the plants are in poor condition with the work of the moth larvae much in evidence. In addition to the eventual destruction of individual plants through larval feeding, infection of the lesions by bacteria and fungi add to the death of the plants. It should be borne in mind, however, that prickly pear seeds can last for several years in the soil requiring monitoring of formerly infested areas from time to time. Introduction of new plantings of these plants is not encouraged.
The Campanulaceae would be familiar to gardeners as the family that is home to campanulas and lobelias, two groups that have been favorite decorative plants for many years. The family is very well represented in the Hawaiian Islands ranking third, after Asteraceae (the asters) and Poaceae (the grasses), as the most species-rich families. Equally, if not more, impressive is the fact that of the 114 species in the family recorded in the most recent flora (the Manual) fully 110 of them are known only from the Hawaiian Islands, although, regrettably, almost a quarter of that number are extinct, and many of the others are rare. This cosmopolitan family is quite large, consisting of 70 genera with about 2,000 species as reported in the Manual, or 79 genera and 1,900 species according to Mabberley (p. 143). The classical view of the family recognized two subfamilies, Campanuloideae, with radialy symmetrical flowers, and Lobelioideae, with bilaterally symmetrical flowers. (A more current view recognizes five subfamilies, but this does not alter the Hawaiian situation.) All of the endemic Hawaiian members of the family fall into Lobelioideae, referred to commonly among island botanists as the lobeliad complex. The remarkable nature of these plants was noted by the famous German botanist Wm. Hillebrand in 1888 when he described them as the “…spectacular pride of our flora.”
The lobeliad complex on the islands consists of the cosmopolitan genus, Lobelia, with a dozen or so species on the islands (there are 300-350 in the genus), and five genera that are unique to the islands: Clermontia with 22 species, Cyanea (including Rollandia) with well over 50 species; Delissea with nine species, seven of which are extinct; Trematolobelia with four; and Brighamia, with two species. (It is worth noting that the generic level nomenclature of the complex may require changes necessitated by relationships revealed by DNA sequence analysis similar to what we saw in Araliaceae.)
Examples of extant species in the complex, based upon the names in the Manual follow, along with comments on ranges of occurrence on the islands.
The Manual lists 14 species of Lobelia on the islands all but one of which are endemics. The decorative species (L. erinus, the edging, trailing, or garden lobelia) is thought to be naturalized in some areas. Lobelia dunbariae (see image), an attractive pale blue-flowered species, occurs on wet cliffs on Moloka`i. Lobelia niihauensis (see image) is a native of dry cliffs on Ni`ihau, Kaua`i, and O`ahu but is seen here in bloom in the Limahuli Garden. Both of these lobelias are considered to be threatened.
Clermontia is a genus of 22 species, one of which, C. multiflora, is extinct, known only from original collections in 1870 (technically, the syntype). Hawaiians refer to the group (lobelias in general) as hähä, `öhä, or `öhä wai. The last name contains the word wai, which means water, suggesting that these plants tend to grow in wet places, which is true in many cases. The examples that follow are species of Clermontia that can be seen quite readily without lengthy or difficult treks.
Clermontia faurei (see image) occurs abundantly along the Pihea Trail in Koke`e State Park (Kaua`i), both in the early part of the board walk and more abundantly along later parts. [This trail is one of the means of access to the Alaka`i Swamp.] Insofar as this is the only species of Clermontia that occurs on Kaua`i visitors cannot mistake it for anything else. The Hawaiian name for this species is hähä`aiakamanu. Taken in one piece this word is quite a mouthful. If we take it apart, however, a story emerges. Hähä we have seen above as a name for these plants in general; `ai is the word for food; a and ka taken together means ‘of the’ and the final term, manu, means bird. The literal translation, according to the Hawaiian Dictionary (Pukui and Elbert, p. 46), is ‘food of the birds’ because the sap of the plant was used to catch birds. According to that reference, however, the plant involved was Clermontia clermontioides. In this instance, I suspect that the use of the plant is more significant than its name; at least they agree at the generic level.
Our next example would involve a bit more effort. Clermontia kakeana (see image) occurs on Maui, Moloka`i, and O`ahu. To see this attractive plant on Moloka`i requires visitors to take the Maunahui Road to the Waikolu Valley Lookout (and picnic area), park their car and walk farther along the access road. Several C. kakeana plants can be found growing beside the road between a quarter and half mile from the parking spot. The road, which requires a four-wheel drive vehicle, has slippery and difficult stretches, and leads ultimately to the trailhead for the Pëpë`öpae Swamp Trail.
This trail is one of the most rewarding nature hikes on the islands (not just on Moloka`i). In order to see this species on Maui it is necessary for visitors to hike along the Waihe`e Ridge (Boy Scout) Trail (accessible by Route 340 northwest of Wailuku), a bit past the 2-mile marker (beyond the wet meadow) where C. kakeana may be seen growing a short distance off the trail (see image).
One of the easiest species of Clermontia to see in its natural habitat is C. parviflora (see image). A visit to the Thurston Lava Tube in Hawai`i Volcanoes National Park is a must stop on visitors’ tours of the island (it’s a regular stop on all bus tours). The plants of interest occur along the steeply descending (paved) path that leads from the view point, and in the vegetation on the right side of the path near the cave entrance. This species occurs only on the Big Island.
The largest genus in Campanulaceae on the islands is Cyanea. The Manual lists 52 species, but several changes—rediscoveries, name changes, status changes—were included in the Appendix all of which makes a detailed discussion of this genus complicated. The numbers from the original chapter, however, offer a useful overview of the genus. Thus, of the 52 listed species at least a dozen were marked as extinct, with another dozen or so marked as rare and/or endangered. The four examples described below should provide the reader with an idea of what to look for when searching for Cyanea.
Cyanea asplenifolia (see image), listed as extinct in the Manual with the last collection recorded in 1920, has been rediscovered on the West Maui mountains. Cyanea fissa (see image), a native of mesic to wet low-elevation forests on Kaua`i was photographed in NTBG greenhouses. Cyanea hardii (see images) is a native of southern Kaua`i, but here seen in cultivation at the Limahuli Garden. The second photograph illustrates the pendulous nature of the flowers which are often difficult to see when looking at the plant from above. Cyanea platyphylla (see image) is a native of the windward side of the Big Island. This specimen was under cultivation at the Rare Plant Nursery in Volcano.
The Hawaiian endemic genus Rollandia was originally erected to accommodate plants that differed from Cyanea on the basis of the relationship between stamens and the corolla tube (Manual, p. 480). The eight species that made up the genus are now considered to belong within Cyanea. Two of the species are extinct, neither having been seen since the early part of the 20th century. All of the extant species occur only on O`ahu.
By comparison, Delissea appears worse off than Cyanea with six of its nine species marked as extinct in the Manual. Of the remaining two, only D. subcordata seems to be holding its own. Delissea rhytidosperma (see image), a rare component of mesic forests on Kaua`i, is under cultivation at the Limahuli Garden.
Trematolobelia is represented on the islands by four species, three of which appear to be faring well. Trematolobelia singularis is the only member of the group that is marked as rare; only a few individuals are known from sites in the Ko`olau Mountains of O`ahu. The species with which I have had the most experience is T. kauiensis (see images), which, as its name indicates, is a native of Kaua`i. Hawaiians know this plant as koli`i.
Visitors who are able to make the hike along the Pihea Trail and survive the scramble over the muddy steps portion and onto the boardwalk proper will be treated to a population of this koli`i in various stages of growth. It is always a pleasure to show first-time visitors this spectacular lobeliad, especially when plants are in flower.
Koli`i is also the name given to T. macrostachys, a species that occurs on all of the main islands except Kaua`i. I have seen this species in the wet forest on Moloka`i in mid May, but it was not in flower (see image). The Big Island endemic species, Trematolobelia grandifolia, has white flowers and larger leaves than the other species. I have not seen T. grandifolia in the field.
Last, but by no means least, is Brighamia, which the Manual describes as “…one of the most unusual members of the Hawaiian flora.” Brighamia comprises two species, B. insignis (see images), `ölulu or pü aupaka in Hawaiian, and B. rockii, pua `ala (fragrant blossom) in Hawaiian. Both species are considered rare and endangered. Brighamia insignis occurs on the sea cliffs of Kaua`i and Ni`ihau; the latter population is likely extinct. Photographs of B. insignis were taken at the Limahuli Garden. Brighamia rockii occurs on the forbiddingly steep sea cliffs of Moloka`i (see image), but may have had a wider distribution (Maui and Läna`i) in the past.
Access to the cliff populations is very hazardous requiring mountain climbing skills or access to a helicopter (or a combination thereof). It is possible to see specimens of B. rockii in an exclosure a short way down the Mule Trail, or in an old planting near the starting point of the trail. Although not in flower (see iamge), the similarity of the Moloka`i plants to the ones on Kaua`i are obvious. Flower color is different, however; in B. insignis flowers are yellow, while in B. rockii they are white. Flowers differ in other more technical ways as well.
Detailed studies of Brighamia, described by C. E. C. Gemmill and coworkers (1998), then at the University of Colorado, provide an excellent opportunity to discuss the phenomenon of extreme rarity. Citing 1991 numbers, those workers reported that the Hawaiian flora consisted of a dozen taxa (genera or species) with only a single individual known in the wild. Thirty-two taxa consisted of from two to 10 individuals in nature; and at least 150 taxa had between 11 and 100. An unspecified number of genera are only slightly better off, one of which is Brighamia. As noted above, Brighamia insignis was at one time known to occur on both Ni`ihau and Kaua`i, but is now known only from the latter. Typical of the history of this species are the population numbers for a site on the cliffs at Näwiliwili (southeastern Kaua`i) (see image): in 1987 there were a dozen individuals; in 1990 only four; in 1992 only three; and in 1996, only a single plant was seen. Brighamia rockii continues to inhabit Moloka`i, although population numbers have decreased significantly over the years. This species may have occurred on Läna`i and Maui, but the lack of reliable records and specimens from these islands place that suggestion in doubt. Brighamia has never been reported from either O`ahu or the Big Island.
The enzyme variation study described by Gemmill and coworkers revealed several interesting features of Brighamia. Whereas the two species are very similar in overall structure—they differ only in flower color, as we saw, calyx shape, length of pedicel (flower stalk), and seed surface—they are genetically quite distinct. This is opposite to the condition of most Hawaiian lineages where species are very different in structure, but very similar in genetic composition. The genetic differences between the two Brighamia species supports recognition of two species. The genetic differences also argue against the hypothesis that the two are related as a progenitor-derivative pair, in which case the derivative species would have been seen to carry a subset of the progenitor genome. This observation leads to the counter hypothesis that the two species were derived from an ancestor that no longer exists.
What has happened to bring Brighamia to such a perilous position? This question is not unique to Brighamia, of course; it has been asked of many of the islands’ rare species. The answer, or answers, to the question would likely apply to most rare plant species on the islands: habitat loss owing to natural events (landslides, hurricanes) and human activities (agriculture, commercial building); competition from alien plant species; the effects of feral animals; and the loss of pollinators. These may work alone or in some combination. Owing to the isolation of most of the populations of Brighamia, human impact may be a minor factor, but competition by alien plants and the destruction wrought by feral animals are likely to have been, and continue to be, major factors. It is interesting to note that the population on Huelo Island, a 3.1 acre islet off the north coast of Moloka`i (see image) is the only one described by the authors as “healthy.” It is noteworthy that the island population is the only one that is free of alien animals, and, of course, it is too small to have appealed to developers. The most important factor leading to the downfall of the species, however, may be the loss of pollinators, since little pollination appears to occur in the nature. By contrast, hand pollination, either in nature or in garden/greenhouse surroundings, is very successful, resulting in capsules with up to one thousand seeds, which, when coupled with near total germination in a controlled environment, can yield excellent yields of seedlings.
There is another aspect of this group of genera that has attracted a great deal of attention in the world of biogeography, the science that is concerned with finding out where the ancestors of the island endemic species came from. Owing to the incredible variation in morphology—gross structures as well as features visible only to specialists—habitat selection, and seed dispersibility, it seemed reasonable to suggest that several colonizations had occurred, with some suggesting that five individual events must have occurred. Similarly, there were differing suggestions as to where the ancestors might have come from. These questions remained unanswered until the very powerful tools of macromolecular analysis became available (Givnish et al. 2008). These methods, which probe the structure of the DNA molecule itself, provide a window into the very changes in the genes that reflect the evolutionary history of the organisms under study. The results from DNA sequence studies of the Hawaiian lobeliads were nothing less than breathtaking. The data clearly and convincingly pointed to the origin of this group from a single colonization event followed by an explosive diversification that produced the array of species we see today! The data also allowed an estimate of the time of that colonization: roughly 13 million years ago.
December 21, 2011