H73 of the Hawaiian Botanical Society volume x ' ^ji MFARTMENT OF BOTANY number i UNIVERSITY OF HAWAII FEBRUARY 1971 f ^ HONOLULU , HAWAII 96822 U AUG i o mo n Nsv-^./flgABIES / DEPARTMENTS Principal paper page 1 Proceedings page 10 Events " 8 Publications " 10 PRINCIPAL PAPER SOME BOTANICAL OBSERVATIONS ON KOA—/ Charles H. Lamoureux — / Introduction Koa, in the broadest sense, includes a number of closely related species and varieties of the genus Acacia native to the Hawaiian Islands and apparently endemic to these islands. The genus Acacia is one of the largest genera of higher plants, including perhaps 500 species native to the tropical and subtropical areas of the world. Of these 500 about 300 are native to Australia, perhaps 50 to Africa, and most of the rest to tropical America and Asia. The African species all possess bipinnate leaves on mature branches, as do most of the American and Asian ones, and need not concern us further as potential close relatives of koa. However, about 250 of the 300 Australian acacias are phyllodineous — the leaves on mature plants are reduced to flattened petioles -- phyllodes -- as is the case with the native Hawaiian acacias. Origin and Dispersal Phyllodineous acacias are also known from New Caledonia, Tahiti, Samoa, Tonga, Fiji, the New Hebrides, New Guinea, the Philippines and Taiwan (Acacia confusa) . From our point of view the most interesting species is Acacia heterophylla native to Mauritius and Reunion Islands of the Mascarene group in the Indian Ocean. This species is so similar to Acacia koa that some of the earliest botanists concerned with the Hawaiian flora considered koa to belong to the species Acacia heterophylla. In fact, Asa Gray, when he described Acacia koa as a species new to science in 1854 stated: "In distinguishing the two trees, peculiar to these most widely separated stations, perhaps I incur the charge of being influenced by geograph- ical considerations rather than botanical characters." However, since we still have 1/ Paper presented at Koa Seminar, sponsored by Institute of Pacific Islands Forestry, U. S. Forest Service, October 9, 1970. 2/ Department of Botany, University of Hawaii. Hawaiian Botanical Society Newsletter - page 2 February 1971 no complete comparisons of Hawaiian koa with the plants from Mauritius and Reunion — , it is probably more in accord with modern biogeographic theory to consider that the two groups are different species, perhaps descended from a common ancestor. This ancestral type, at least for koa, was probably a species such as Acacia melanoxylon. the blackwood of Australia. All but one of the botanists who have con- sidered the origin of koa in any depth have suggested that its closest relatives are species from Australia or some of the islands in the South Pacific (in addition to the Mauritius species). The only exception was Forrest Brown, who attributed the origin of the bulk of the Hawaiian flora to Tropical America while essentially all other workers have considered that most Hawaiian plants have their closest relatives in the Australasian regions. Brown (1921) wrote: "a cusp-pointed phyllode of the same size and outline as the Hawaiian Acacia koa var. lanaiensis has been found in the American Lower Eocene." Despite Brown's comments, I think we must look toward the south and west for the original immigrant which, once established in Hawaii, developed into our native acacias. How did the first seeds get here from Australia or the Australasian region? Acac ia seeds are obviously too heavy to be carried by wind currents. Rock (1919) suggested that they were carried here by birds which "do not exist today" (in Hawaii) , "but were in all probability the now extinct columbae and their relatives." On the other hand, Carlquist (1966) has suggested that rafting was responsible for the seeds which reached Hawaii from elsewhere. Although seeds of Hawaiian koas will not float, Carlquist suggested that perhaps a branch bearing unopened but mature seed pods could have drifted here. In Acacia simplicif olia , from Samoa and Tonga, each seed is contained in a loment-like segment which contains an air space sufficient to float the seed for at least a few days. This is not a very efficient means of dispersal but one which might have been successful at least once during the past 20 million years or so. Carlquist further suggested that koa could have been distributed among the islands, once it reached here, by seed-eating birds such as Psittacirostra. All we really know, then, is that koa got here, by some natural means, from some other area - the rest is all speculation at this stage. But, while we're speculating, let's go one step further and suggest that the immigration of the ancestors of koa to Hawaii probably occurred only once, and that this one occurrence was some time ago (on the order of perhaps a few million years). The arguments in favor of a single introduction rather than repeated introductions are twofold - first, the chances of the occurrence of a successful natural introduction to Hawaii are fairly small when the dispersal mechanisms available are no more efficient that they are in these acacias, and thus the probability of two successful introductions at different times from the same source is extremely small; second, the Hawaiian acacias seem to be fairly closely related, and it is probable that they have developed from a single ancestral type. The evidence in favor of a relatively long time since the ancestors 3/ After this paper was delivered, Mr. Craig Whitesell called to my attention a recent paper by Vassal (A propos de Acacias heterophy 11a et koa . Bull. Soc. d'Hist. Nat. de Toulouse 105:443-447. 1969) who demonstrates that on the basis of corolla structure, fruit and seed size, and morphology of the first two leaves on the seedlings, Acacia heterophylla from the Mascarene Islands differs signifi- cantly from A. koa of Hawaii. Vassal therefore considers the two species to be distinct. He also reports that in A. heterophylla , as in A. koa, the chromosome number is 2N = 52. Hawaiian Botanical Society Newsletter - page 3 February 1971 of koa became established in the islands is also of at least two types - first, the fact that local populations have become established to the extent that taxonomists have recognized at least three species, one of which has three varieties; second, a large number of endemic insects restricted to koa have also had time to evolve (Swezey, 1954; Gressitt & Davis, 1969). Taxonomy There are five taxa of Hawaiian acacias which are more or less generally recognized. These are: 1. Acacia koa (Gray, Bot. U. S. Expl. Exped. 480. 1854, variety koa (A. heterophylla Willd. according to Gaudichaud and according to Hooker and Arnott) . 2. Acac ia koa Gray var . lanaiensis Rock, T. H. Bd. Agr. For. , Bot. Bull. 5:21. 1919. (A. koa B var. Hillebrand, Flora Haw, Isl. 113. 1888). 3. Acacia koa Gray var. hawaiiensis Rock, T. H. Bd. Agr. For. , Bot. Bull. 5:23. 1919. This is the type with broad phyllodes from Hawaii. It is of special interest as it is the type most likely to be used as a source of timber. It should be noted that Gray (1854), Hillebrand (1888), and Skottsberg (1944) did not consider this taxon to be distinct from var. koa . 4. Acacia koaia Hillebrand, Flora Haw. Isl. 113. 1888. 5. Acacia kauaiensis Hillebrand, Flora Haw. Isl. 113. 1888 Table I gives the distribution of these taxa and a list of their distinguishing features as indicated by Rock (1919; 1920) and Judd (1920). This summarizes our know- ledge of the systematics of Hawaiian acacias, which is not in a very satisfactory state. We really need to make careful and complete collections from throughout the islands, and to study them using modern techniques. For example, there is only one recorded chromosome count for "Acacia koa" (2N = 52, Atchison, 1948). This is of interest as the other phyllodineous species reported by Atchison had 2N = 26, suggest- ing that the Hawaiian material he studied was tetraploid. A complete cytological study would be most helpful in interpreting the evolutionary history of Hawaiian acacias. Little attention has been paid to characters exhibited by the juvenile foliage. While the wood anatomy of A. koa and A. koaia has been described (Brown, 1922; Lamberton, 1955), there have been no other anatomical studies. Newer methods of comparisons of bio-chemical constituents using electrophoretic and chromatographic techniques might provide useful systematic information. We know that koa varies morphologically from place to place, but we really don't have any idea how much of this variation is genetically controlled and how much is environ- mentally controlled. For example, both Rock (1919) and Judd (1920) suggested that the broad phyllodes of var. hawaiiensis are a response to high altitude with conse- quent fog and mist. Rock even cited an example of var. hawaiiensis grown from seed in San Francisco which had wider phyllodes than any observed in Hawaii. Yet, on Hawaii, although there is considerable variation in phyllode width, not all the plants with very broad phyllodes are restricted to higher, moister areas. In Kipahulu Valley on Maui , on the other hand, koa grows in areas which seem to be wetter than most other areas in the islands where it is found, yet the phyllodes are quite narrow. I suspect that we are dealing with both genetic and environmental factors here. Hawaiian Botanical Society Newsletter - page 4 February 1971 r-l 33 G G G G . G G 33 • CO -X •» & G g G G 50 0) co i-H G g o C £ > G 3 G E M G £ G G •l—l G 42 •rH CO G G G iM c G CO O O CO 1 B o G CX o . 3 45 G CN G 3 c i—H G G •rl G G G g O co G i — 1 G X G 3 50 I 1 O ?— 1 G G g 43 r •H G d) G 45 +» C 50 CM o x G G CO co 50 X a O ** "(—1 3 CM G 53 rM O G G 0) G a G G G G •H r. 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