Part 32 Passifloraceae - Phytolaccaceae
Passifloraceae, the passion flower family, consist of 25 genera with 725 species that occur in warm and tropical habitats with a concentration in the New World. Four hundred and thirty of those species comprise the genus Passiflora, the true passion fruits. There are no endemic members of the family in the Hawaiian Islands, but a dozen have become naturalized, including P. edulis (see image), the principal passion fruit of commerce, known also as the purple granadilla, purple water lemon, and, in Hawaiian, liliko`i. This species, or at least its flavor, would be familiar to anyone who has ever sipped a can of Pass-O-Guava Nectar or enjoyed a slice of Hawaii’s own dessert, haupia liliko`i pie. The beverage is a mixture of three tropical fruits, passion fruit, orange, and guava; the pie is a layered concoction of a stiff coconut cream on the bottom with a topping of jellied passion fruit juice. Liliko`i sauces can be encountered with barbequed chicken among other offerings in many ‘traditional’ restaurants in the islands.
There are two varieties, or forms, of liliko`i growing on the islands, var. (or forma) edulis, which was brought to the islands in about 1880; and var. (or forma) flavicarpa, with larger, yellow-colored, better-tasting fruit, which was brought to the islands in 1923 by the Hawai`i Agricultural Station. The latter yields the fruit of commerce.
Although not quite as aggressive as banana poka, which we will meet in some detail below, but nonetheless an unpleasant intruder, is P. suberosa (see image), known as the cork vine, or huehue haole (alien huehue). Huehue is Cocculus trilobus (see under Menispermaceae). The common name cork vine comes from the thick, cork-like material that accumulates on the stems of this climber as it matures (see image). (Note: the Latin word for cork is suber, hence the specific epithet, suberosa.) Not only is this material unattractive, it is potentially harmful to the plant on which the vine is growing owing to the accumulated weight.
Other passion flowers that are commonly seen in the islands are P. subpeltata, the white passion flower (see image); and P. foetida(see images). This latter species is known by various names including love-in-a-mist, running pop, wild water lemon, lani wai on Ni`ihau and pohäpohä elsewhere in the islands.
The last passionflower that we will meet is one that ranks among the worst offenders among the islands' alien opportunists. Originally identified as P. mollissima in the Manual, recent studies suggest that the correct name for this species is P. tarminiana (personal communication from Forest Starr). This beautiful species (see image) is a native of the Andes, where its fruit is an item of commerce. It was first planted on the Island of Hawai`i in 1921, with subsequent introductions to other sites on the Big Island and then on Maui and Kaua`i.
The common name, banana poka, is a description of the banana-like fruit of the plant with the descriptive Hawaiian word poka (which is the same as moka; (Pukui and Elbert, p. 251) meaning offal, waste matter, refuse or filth. This seems a fairly clear value judgment; although the fruit is edible, the invasive nature of the plant outweighs its positive virtue. I have seen the suggestion made that the term poka is a Hawaiian word meaning "to climb." I have not seen this definition in the Hawaiian Dictionary where the word to climb is given as pi`i (Pukui and Elbert, p. 327). Reference to climbing certainly makes sense, however. Further information on this point would be appreciated.
In the case of firetree (Myrica faya, which we met above in Myricaceae) we saw an example of an invasive plant capable of altering its environment so drastically that native species cannot compete. In the case of banana poka we have a plant that employs a different strategy: it overwhelms native species by its opportunism and capacity for rapid growth. The combination of availability of abundant disturbed sites, mainly caused by pigs; an abundance of dispersal agents; a wide ecological tolerance; a lack of enemies large or small; and a very vigorous life style explains banana poka's success as an invader. It also matures early, reproduces continually, and produces a large seed crop. Another feature is the production of large number of seedlings in the vicinity of a mature plant that are held in a state of suspended growth until light conditions are favorable for growth. Growth rates vary as a function of light with a maximum rate in the neighborhood of 10 feet (3 m) per year under favorable conditions. In addition to early reproductive maturation, banana poka has a dual reproduction system: it is an out-crossing species early in its life but becomes a self-pollinator as it ages, enabling an isolated individual–resulting from a seed deposited by a pig or bird–to become established.
The size of infestations, and the speed at which they became established, offer an opportunity to appreciate how devastating an invader banana poka is. The five major infestations, three on the Big Island, and one each on Maui and Kaua`i, all resulted from intentional plantings. The Big Island sites are the `öla`a Tract in Hawai`i Volcanoes National Park; the Laupähoehoe population, on the eastern flank of Mauna Kea; and the Kaloko population in North Kona. LaRosa described the expansion of the `öla`a Tract population as explosive over the ten year period 1971-1981. During that decade the area of infestation rose from 350 to 5,775 acres (142 to 2,338 ha). This rapid expansion was credited to a major wind storm that struck the area in January 1980, which means that the majority of expansion is thought to have occurred during the years 1980 and 1981.
Expressing the impact of this plant in a different way, the density of plants in the Laupähoehoe population is reckoned to be greater than 202,000 individuals per acre (ca. 500,000 per hectare), which represents 75 -100% cover. Banana poka was planted in this area in 1928 and expanded rapidly owing to the availability of sites that were highly disturbed owing to grazing and logging activities. The population appears to be stable having declined only 3% during the 1971-1981 study period.
The 1990 wind storm that wreaked havoc on the forest of the Big Island was not an isolated incident. In November 1982 the eye of Hurricane Iwa passed about 25 miles (40 km) to the north of the northwestern coast of Kaua`i in what was to that date the costliest storm ever to hit the islands. Kaua`i, Ni`ihau, and O`ahu experienced severe devastation. Forests on Kaua`i were particularly badly damaged with great swathes of native trees laid to waste. The resulting openings in the canopy provided almost unlimited opportunity for explosive growth of banana poka. This area was hit again in 1992, this time by Hurricane Iniki, which is reckoned to have been even more destructive. I have not seen numbers on the level of forest devastation brought about by Iniki, but having visited the area in 1994, it was clear that one did not really need numbers to appreciate the impact of the hurricane.
Hurricanes have been a part of the Pacific weather scene for a very long time; the Hawaiian Islands would certainly have experienced their fair share of storms, some probably as violent as Iwa and Iniki. Such events would have no doubt been destructive, but the islands would have healed themselves and life, in time, would have returned to normal. It seems unlikely to me that any of the plants brought by the Polynesian colonizers would have had the potential destructive power of those brought by post-contact visitors, although kukui nut, Aleurites moluccana, has moved into some lowland forests. It should be noted, however, notwithstanding the apparent benign nature of the "canoe plants," the same cannot be said about the human colonists themselves, a subject that will be discussed briefly below.
One of the easiest ways to see banana poka is to visit the Koke`e area on Kaua`i where plants can be found along the highway leading into the park area as well as along the road to the Kalalau Lookout. A short walk along the access road will give visitors an opportunity to see individual plants growing at shoulder height over native shrubs, a common growth form when there are no large trees to climb (Passiflora7.jpg). An interesting exercise is to find an end of a vine and tug on it to see how far it has grown from its source. If you feel like pulling the plant out by the roots, feel free to do so, no one is going to scold you. Another interesting sight along the road leading to the park is the combination of banana poka growing intermixed with two other alien species, Fuchsia boliviana, which was illustrated above and Tropaeolum majus (See below). We know the problems associated with banana poka. Tropaeolum majus, the common garden nasturtium also has the capacity to become a pest in the islands where it can compete with native ground cover species. There were efforts a few years ago to eradicate it from at least one kapuka on the Mauna Loa Strip Road, which appears to have been successful since I saw none on my most recent visit to the area (2010).
Much of the information in this section was abstracted from an article by Anne Marie LaRosa (1992), which came from her studies of banana poka for a M.Sc. degree from the University of Hawai`i.
There are two species of pokeweed in the islands, the naturalized Phytolacca octandra (see image), a native of the Neotropics; and the endemic P. sandwicensis, pöpolo kü mai or pöpolo. The naturalized plant pictured here was growing in a disturbed site near the mule trail on Moloka`i. The most characteristic feature of these plants are their shiny, purple berries, which are poisonous. I have not seen the endemic species, at least in flower or fruit, so I have borrowed two beautiful images of this species' flowers and fruits from Dr. Gerry Carr's collections of images of native plants (see image).
LaRosa, A. M. 1989. The status of banana poka in Hawai`i. pp. 271-299. In C. P. Stone, C. W. Smith and J. T. Tunison (eds.). Alien plant invasions in native ecosystems of Hawai`i: management and research. University of Hawaii Press, Honolulu.
June 13, 2012