The Polynesian Species of Myoporum1 GRADY 1. WEBSTER2 INTRODUCTION trade, but neither then nor since has the naio THIS REVISION was originally begun as an attained any real commercial value. Brown analysis of the notoriously polymorphic (1935:. 279) reports that on the island ofRapa species Myoporum sandwicense of the Hawaiian (in southern Polynesia) naio wood is used Islands. After a considerable amount of work for building canoes and houses . had been done, however, it was found that The real value ofMyoporum to the Hawaiian the forms of Myoporum from southern Poly­ Islands resides in its role in the formation of nesia were very similar. Because of the close­ a dry forest cover and in the consequent ness of relationship, it seemed both more checking of soil erosion. On most of the is­ practical and more worth while to treat all of lands the dry forest region has been partially the Polynesian species together. or completely denuded, with serious conse­ In the Hawaiian Islands, Myoporum sandwi­ quent erosion. Reforestation work has been cense is an evergreen shrub or tree which carried out chiefly with quick-growing exotic grows mostly in dry forests on leeward slopes trees such as Casuarinaand Eucalyptus, but the from sea level to an altitude of 10,000 feet. appearance of the resulting vegetation is dis­ Its plasticity in habit is remarkable, as it may appointing from an esthetic point of view. It become a tree 15 meters high in the dry is to be hoped that eventually the original dry forests (Rock, 1913: 427) or a creeping , forest trees, such as native species of Dio­ fleshy, prostrate shrub on the beaches and low spyros, Acacia, Sophora, and Myoporum, will rocky islets. More rarely it may even invade regain a part of their lost dominance. Egler the rain-forest, as in Waikolu Valley on (1947: 425), studying the communities of the Molokai. dry southeastern section ofthe Koolau Range The Hawaiians used the species, which they on Oahu, predicted that although Myoporum called naio, for timber in building houses was rare at that time it might in the future as­ (Brigham, 1908: 83). Apparently it was not sume an important place in the Prosopis com­ cultivated, as it is in Rarotonga (Wilder, munity. 1931: 100), for the perfume of the flowers. Acknowledgments: Dr. Harold St.John ofthe There are references (Bennett, 1832: 257; University ofHawaii originally suggested this Hooker and Arnott, 1841: 93) concerning the study, made it possible to collect and observe attempts of traders of the 1820's to substitute the plants in the field, and has been of great naio wood for sandalwood in the Chinese assistance in criticizing and offering sugges­ tions for the manuscript. Mr. Otto Degener 'Part of a th esis submitted in partial fulfilment of re­ loaned his large and important collections for quirements for th e degree of Master of Arts in Botany at the University of Texas. Manus cript received Sep­ study and discussed with me .some of the tember 22, 1949. forms which I was unable to s~e in the field. 2Former grad uate assistant in Botany, University of Dr. B. C. Tharp readily consented to having Hawaii , and Teach ing Assistant in Biology, Unive rsity of Texas; now at the Herbarium, University Museum, the study continue at the University ofTexas, University of M ichig an. and he and Dr. W. Gordon Whaley kindly [52 } Polynesian Species of Myopomm- WEBsTER 53 read and criticized the manuscript. I also wish that so far no really satisfactory subdivision to thank Miss M arie Neal for making avail­ of the genus has been made. able the facilities of the Bishop Museum The H awaiian species M . sandwicense was Herbarium, Miss Mary Lou Jeffrey and Mr. apparently first collected by Archibald Men­ William 1. Brudon for drawing the illustra ­ zies on Vancouver's expedition and was at tions , and the curato rs of the herbaria listed first referred 'to the New Caledo nian M . below for the loan of specimens : tenuifolium by H ooker and Arnott (1841: 93). Bishop Museum, H on olulu (BISH ) ; Bois­ It was described as a new species, Poly­ ser Herbarium, Geneva (G-BOIS); Otto coelium sanduiicense, ' by D e Cand olle (1847 : Degener, personal herbarium (DE G); Deles­ 705) and was redescribed in the genus sert Herbarium, Geneva (G-DEL); Gray Myoporum by Asa Gray (1866: 52). No other Herbarium (GH ); Royal Botanic Garden s, name was officially prop osed for any of the Kew (K ); New Yo rk Botanical Garden (NY) ; .Hawaiian plants until Leveille (1912: 63) Laboratoire de Phanerogamie, Paris (P); Riks­ published M. Fauriei based on a Faurie museum, Stockholm (S); University ofTexas , specimen from the island of Hawaii. Kraenz­ Austin (T); Naturhistorisches Museum, Vien­ lin (1929: 21)reduced the species to a variety na (W). but app ears to have misapplied the name to specime ns of var. sandwicense. TAXONOMIC POSITION Hugh Cuming had collected Myoporum in The genus Myoporum consists of about 30 the Austral Islands (Tubuai) in 1828, but species scattered over a wide area including over a hundred years went by before any new M auritius, Australia, N ew Zealand, New species were described from southern Poly­ Guinea, China, Japan, Micronesia, and Poly­ nesia. Cheeseman (1903: 291) listed as nesia. It is characteri zed by its relatively Myoporum sp. a M angaian plant culti vated actinomorphic corolla and its fleshy drupe on Rarotonga. Wilder (1931: 100) I referred with usually solitary ovules in the cells. Like the Rarotongan plant to M . sandwicense, but other genera in the M yoporaceae, Myoporum Skottsberg (1933: 165) described it as a new has axillary flowers. .stamens with confluent species-M. Wilderi-and discussed its prob­ anther cells, pendent anatrop ou s ovules, and able relation ships to most of th e other in­ gland -dotted, alternate leaves . The Verbe­ sular species. Two years later Brown (1935: naceae is probably the most closely related 277) published th ree species from the Austral family, but it is well distinguished by its Islands and Rapa . ovules which are not apically attached and Variation in the Hawaiian myoporums has by its opposite leaves which lack internal been discussed by Skottsberg in his paper on 'secretory tissue (Solereder, 1899: 711). M . Wilderi and by Degener (1930: 261), The Polynesian species of Myoporum be­ but neither has published any new names long to section Pentacoelium of Gra y (1866: altho ugh D egener illustrated a pubescent­ leaved form and anno unced 'his intention of 51), which has priority over the more ap­ describing it in his Flora Hawaiiensis. propriate name Eumyoporum of Bentham (1870: 2). Wettstein (1895: 360) disting uish­ MORPHOLOGICAL CRIT ERIA ed three sections which contained Pacific Because of the extreme polymorphism of insular species- Pentacoelittm, Polycoelium, and many Hawaiian populations of Myoporum it Eumyoporum- but there is no justificatio n for is difficult to find morph ological characters placing these insular species in more than which do not vary as much between indi­ one section . Kraenzlin's sections (1929: 15) viduals as between varieties. An accurate are even more poorly founded; so it seems concept of the range of variation-arrived at 54 PACIFIC SCIENCE, Vol. V, January, 1951 by observation of a great many specimens­ often to be a response to wounding caused is essential in defining the taxonomic charac­ by grazing animals, although in some cases ters of the various groups. the lower "sucker" shoots from an uninjured Growth habit, as has been indicated, is so plant may bear pubescent leaves. In fact, greatly modified by environment that it is even if the leaves on basal or wound shoots probably of no taxonomic significance. The are not pubescent, they are often serrate and stem is significant only in distinguishing var. larger than normal leaves. Furthermore, there stellatum from var, Degeneri, the former hav­ is evidence that at least in some groups of ing pubescent br~nchlets. Myoporttm sandwicense the "juvenile" leaves There are many leaf shapes but few of of a: young plant are of the abnormal serrate­ them are constant in anyone population. pubescent type, while those formed later are Serrate margins are found sporadically among entire and glabrous. Further investigations nearly all the Hawaiian varieties and must be . on this subject are much to be desired. used with extreme caution as a taxonomic The number of flowers in the axillary character. On the other hand, this serrature is clusters varies not only between plants but constant in the southern Polynesian forms even on the same branch and thus does not and may be used dependably to separate M . appear to be of any great taxonomic value. Stokesii from M. rapense. Conspicuous dif­ The same can be said of the flower pediceJs, ferences in leaf texture occur among the which vary, widely, but inconsistently, in Hawaiian plants, but in the main these appear length and thickness. to reflect environmental differences. The The number and length of the calyx lobes, relative conspicuousness of the nervation within certain ranges of variation, are sig­ depends in turn on leaf texture and is thus nificant, while their shape (on account of its obviously unreliable. plasticity) is usually less so. The size and The leaves of all the Polynesian species shape of the corolla have not been used for have subepidermal pellucid-punctate tissue, distinguishing varieties; although there are and the distribution and type of these pel­ readily apparent differences, they are over­ lucid spots appear to be good specific cri­ lapping and inconstant. The amount of teria. M. Stokesii and M. rapense are difficult to pubescence on the corolla throat is usually separate from the New Zealand M .