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Observations on Hawaiian Species of Wikstroemia

(Angiospermae: Thymelaeaceae) 1 SAMTA GUPTA and G. W. GILLETT2

Wikstroemia (Thymelaeaceae) is a genus of most thoroughly by Skottsberg (1936, 1944a, tropical and subtropical shrubs or trees, widely 1964), yet the identification of the Hawaiian distributed in southeast Asia to Malaysia, north­ species is extremely difficult. The published east Australia, and the Pacific islands (Ryukyu, morphological descriptions are often inconsistent Marianas, Caroline, Hawaiian, Society, Mar­ and ambiguous. Every study has resulted in the quesas, Tonga, Fiji, Norfolk, and New Cale­ addition of more species. Skottsberg recognized donia). The Hawaiian species are known by the a total of 22 species (Table 1). Of these 22 name Akia or Akea. species, 14 are restricted to one island: 4 to The genus Wikstroemia was described by Oahu, 2 to Kauai, 3 to Maui, 1 to Molokai, 1 to Endlicher in 1833 from Norfolk Island. The Lanai, and 3 to Hawaii. The remaining 8 species type species is Wikstroemia australis. Many new are found on more than one island. species have since been described. Some species Extreme diversity in the general morpho­ were further divided and some segregates were logical expression, habit, and habitat preference accorded specific rank. Ohwi (1965) mentioned occurs in the Hawaiian species of Wikstroemia. 50 species, while Ding Hou (1960) estimated They occur on well-drained to poorly drained 70 species in the genus. However, a total of at soils and also on arid habitats of lava flows. least 161 species names have been recognized. This habitat diversity can be found within a Meisner (1857) divided the genus into two single species. The genus occurs from sea level sections: Diplomorpha (albuminous seed, to 1800 meters, under moisture regimes varying ebaccate, nonsucculent fruit); and, Euwik­ from 0.5 to 5 meters per year. In native vegeta­ stroemia (= Wikstroemia) (exalbuminous seed, tion, the plants often occur associated with baccate and succulent fruit). Ding Hou (1960) Scaevola, Metrosideros, Diospyros, etc. reports that in the Malaysian species of section Duration of flowering is 3 to 5 months, Wikstroemia there is morphological variation generally from May through September, but this not only within a single species, but also in the varies in different species and in different locali­ flowers of one specimen. He also quotes a ties. Populations obtain ingress to new territory similar observation, by Peterson, for African probably through the dispersal of the drupaceous Thymelaeaceae. The Hawaiian species of Wik­ fruits by birds. stroemia all belong to the widely distributed The habit of the Hawaiian species is highly section Wikstroemia that Ding Hou recognizes variable. Plants are procumbent to erect; low as a· subgenus. In this subgenus there are 6 shrubs to small trees. This variation can be species in the Philippines, 3 in New Guinea, 1 found within a single species and even in the in Fiji, 5 in Borneo (Ding Hou, 1960), 1 in same population. Samoa, 7 in Japan (Ohwi, 1965), and 22 in Above all, the morphological features of the Hawaii. This indicates a remarkable speciation leaves, flowers, and fruits are most variable. The of Wikstroemia in the Hawaiian Islands. leaves in this genus vary from 2.5 to 16 em in The Hawaiian Wikstroemia have been studied length and 0.7 to 4 em in width. Variation in by Gray (1865) and Hillebrand (1888), and the texture of the leaves has been noticed within a single species. The length of the inflorescence 1 Abstracted from a thesis submitted by the senior rachis varies from less than 1 mm long, or author in partial fulfillment of the requirements for nearly capitate, to 150 mm long and distinctly the degree of Master of Science at the Graduate School, racemose. Hillebrand (1888) cites the extensive University of Hawaii. Manuscript received April 30, 1968. variability in the flowers of this genus. We have 2 University of California, Riverside. observed that the flowers of a single species may 83 84 PACIFIC SCIENCE, Vol. XXIII, January 1969

TABLE 1 ported by Fagerlind (1940) in the widely dis­

THE HAWAIIAN SPECIES OF lJ7ikst1"Oemia tributed Asian species, W. indica.

SPECIES REFERENCES MATERIALS AND METHODS 1J7. sandwicel1sis* Meisner (1857) Collections of Wikstroemia were made from 1J7. elongata Gray (1865) IV buxifolia Gray (1865) the islands of Kauai, Maui, Hawaii, Molokai, IV uva-ursi* Gray (1865) and Oahu. Populations sampled are given in IV phillyreifolia* Gray (1865) Table 2. W. hanalei Wawra (1875) 1J7. bicornuta Hillebrand (1888) Cytological Stttdies W. villosa Hillebrand (1888) IV oahuensis* Rock (1913) All chromosome studies were made from the IV furcata* Rock (1913) microsporocytes. The young flower buds were 1J7. recurva* Skottsberg (1936) collected and fixed (by placing in chloroform­ W. haleakalensis Skottsberg (1936) ethanol-acetic acid 4:3: 1) for 24 to 48 hours, W. leptantha* Skottsberg (1936) 1J7. caumii Skottsberg (1936) then transferred to 70 per cent ethanol-water 1P'. pulcherrima* Skottsberg (1936) and stored in the refrigerator until used. IF'. sellingii* Skottsberg (1944a) Microsporocytes were removed from the an­ 1J7. skottJbergiana Sparre (1964) thers by dissection and smeared in acetocarmine. IV isae* Skottsberg (1964) The slides were stored in the refrigerator (12 W. vacciniifolia* Skottsberg (1964) W. forbesii* Skottsberg (1964) to 24 hours) until stained to the desired inten­ 1J7. eugenioides* Skottsberg (1964) sity. W. lanaiensis Skottsberg (1964)

• Chromosome counts obtained in this study. OBSERVATIONS AND RESULTS be unisexual or bisexual within the same popu­ Chromosome counts of 27 populations were lation (Wikstroemia oahuensis) or in different determined (Fig. 1), these representing the 13 populations (W. phillyreifolia). The length of species listed in Table 2. These counts show that the floral tube was found to be shorter in the all populations, with the exception of the one female flowers, longer in the male flowers of of Wikstroemia pulcherrima, are diploid with some species. The fruit shape ranges from ellip­ 9 pairs of chromosomes. The one population of soid to fusiform to globose and varies in color W. pttlcherrima has the chromosome comple­ from yellow to orange to red. ment of 18 pairs (Fig. 2), confirming the From this information it is evident that the earlier somatic count on this species by Skotts­ use of morphological features in the demarca­ berg (1953). This population is characterized tion of species in this genus often results in by aberrant chromosome pairing (see multi­ uncertain determinations. valents in metaphase I chromosomes in Fig. 2), In recent years cytological data have been and by the unequal segregation of chromosomes used successfully as important criteria in taxo­ in anaphase 1. The plant studied had a relatively nomic work. The chromosome number often low fertility, the percentage of "good" pollen shows a high degree of stability within a species being 55 in 1,000 grains observed. These ob­ and often correlates with the natural grouping servations suggest that this is an autotetraploid. of species. More important, chromosome studies Our studies of flower morphology indicate often reveal critical information on evolutionary that floral dimorphism is present in all 13 dynamics, and this information aids in the inter­ species studied, confirming earlier observations pretation of difficult genera such as Wikstroemia. by Skottsberg (1936, 1944a) and Carlquist Skottsberg (1953) has reported chromosome (1966). However, we have found bisexual as counts for two Hawaiian species: Wikstroemia well as unisexual flowers in three species: Wik­ ttva-ttrsi (from Kauai, 2n = 18, and Maui, stroemia phillyreifolia (Gupta 132, 313, and 2n = 72); and W. pulcherrima (from Hawaii, 314), W. oahtJensis (Gupta 268), and W. fttr­ 2n = 36). An apomictic triploid has been re- cata var. fmcata (Gillett 2104, 2105). Our Hawaiian Wikstroemia Species-GuPTA AND GILLETT 85

TABLE 2

lVikstroemia CHROMOSOME NUMBERS, COLLECTION DATA, AND SPECIES

SPECIMEN LOCATION AND CHROMOSOME NUMBER ELEVATION SPECIES NUMBER Gupta 136-2 Wiliwilinui Ridge, Koolau Range, lV. oahuensis n=9 Oahu (600 m) Gupta 142 Aiea Loop Trail, Koolau Range, W. oahuensis n=9 Oahu (400 m) Gupta 160 Kipapa Gulch, Koolau Range, lV. oahuensis n=9 Oahu (520m) Gupta 17S Waahila Ridge, Koolau Range, 119'. oahuensis n=9 Oahu (50 m) Gupta 130 Bishop Museum, Oahu (50 m) W. uva-ursi n=9 Gupta 139 Kawai-iki Ditch Trail, Koolau W. sellingii n=9 Range, Oahu (400 m) Gupta 141 Aiea Loop Trail, Koolau Range, W. sellingii n=9 Oahu (400 m) Gupta 14S Halemano Intake No.1, Koolau W. isae n=9 Range, Oahu (400 m) Gillett 2104 Halemanu, Kokee, Kauai (1200 m) W. fut'cata var. fut"cata n=9 Gillett 2105 Halemanu, Kokee, Kauai (1200 m) W. fut"cata var. furcata n=9 Gupta 149 Haena-Kalalau Trail, Haena, W. fut"cata var. palustris n=9 Kauai (SO m) Gupta 167 Haena-Kalalau Trail, Haena, W. furcata var. palustt"is n=9 Kauai (SO m) Gupta 170 Haena-Kalalau Trail, Haena, W. fut"cata var. palustris n=9 Kauai (SO m) Gupta 174 East of Kokee, Kauai (1200 m) W. furcata var. palustris n=9 Gupta 155 Kawailoa Summit Trail, Koolau W. recut"va n=9 Range, Oahu (1200 m) Gupta 176 Waahila Ridge, Koolau Range, W. eugenioides n=9 Oahu (50 m) Gupta 200 Puu Kanehoa Trail, Waianae W. leptantha n=9 Range, Oahu (700 m) Gupta 223 Road to Mt. Kaala, Waianae lV. leptatltha n=9 Range, Oahu (SOO m) Gupta 304 South slope of Haleakala above W. vacciniifolia n=9 Kanaio, E. Maui (600 m) Gillett 2005 Lahainaluna, Maui (900 m) W. vacciniifolia n=9 Gupta 311 Near Black Sand Beach, Chain of 119'. sandwicensis n=9 Craters Road, Hawaii (60 m) Gillett 2061 45 miles south of Kona, Hawaii 119'. sandwicensis n=9 (600 m) Gupta 314 Near Black Sand Beach, Chain of W. phillyreifolia n=9 Craters Road, Hawaii (60 m) Gupta 315 15 miles northeast of Volcano W. phillyreifolia n=9 House, Hawaii (750 m) Gupta 31S Pahala; 51 miles from Hilo, W. phillyreifolia n=9 Hawaii (400 m) Gillett 2109 Above Kaunakakai, Molokai (350 m) W. fot'besii n=9 Gupta 322 Parker Ranch, near Puu Waawaa, W. pulchet'1'ima n = IS Hawaii (SOO m) Gupta 324 Parker Ranch, near Puu Waawaa, 119'. pulchen'ima n = IS Hawaii (SOO m) 86 PACIFIC SCIENCE, Vol. XXIII, January 1969 1 t.,. ~ . (" ..&' ...... -" ~ , . ". ••c A B ~, • ..-", ",-- ~. 1 0 .. F CS E - ., .. , ,. '---',l ". ... ,. '--" ~ #I -..." ,:~). '. • G .'H

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FIG. 1. Drawing of meiosis in microsporocytes of Hawaiian lVikst,-oemia. A, lV. oahuensis (Gupta J 42) ; B, lV. sandwicelZSis (Gillett 2061); C, lV. leptantha (Gupta 200); D, lV. l'ecul'va (Gupta 155); E, lV. fur. cata var. palust,-is (Gupta 149); F, lV. sellingii (Gupta 139); G, lV. isae (Gupta 148); H, lV. eugenioides (Gupta 176); I, lV. uva-uni (Gupta 130); ], lV. philly,-eifolia (Gupta 314); K, lV. vacciniifolia (Gillett 2005); L, lV. fu,-cata var. furcata (Gillett 2104); M, lV. fo,-besii (Gillett 2109). Hawaiian Wikstroemia Species-GuPTA AND GILLETT 87

high level of outcrossing. All species studied are characterized by floral dimorphism, and various levels of dioecism, monoecism, and polygamodioecism prevail. These conditions fa­ cilitate a strong expression of outbreeding. The presence of bisexual flowers in three species shows that outbreeding may not be an exclusive system, and that a measure of inbreeding may take place. The perfect flowers studied have the stigma close to the anthers, so that self-pollina­ tion is possible. There is no evidence of di­ chogamy in these flowers, so that barring self­ incompatibility, a most unlikely possibility, there is every opportunity for inbreeding. Lastly, there is strong cytological evidence of inbreeding in the putative autotetraploid, Wikstroemia pul­ FIG. 2. Drawing of meiosis in microsporocytes of cherrima. Wikstroemia pulcherrima. Left: metaphase chromo­ The great diversity in the Hawaiian species of somes showing 7 quadrivalents (on the right) and 4 bivalents (on the left). Right: anaphase I showing Wikstroemia may be due to hybridization be­ segregation of 18 chromosomes (above) and 18 chro­ tween species. Skottsberg (1936) suspected hy­ mosomes (below). bridization in this genus. He cited specimens that are similar to what Gray described as observations show that monoecism, dioecism, W. buxifolia but indicated that he suspected and polygamodioecism are present in the Ha­ them to be hybrids of W. phillyreifolia and waiian species of Wikstroemia. W. sandwicensis. We have observed W. sel­ lingii and W. leptantha growing together DISCUSSION along the road to Mt. Kaala, Oahu. Also, we have seen W. isae and W. sellingii in the same A limited cytological study of Wikstroemia population near Halemano Intake No.2, Koo­ in Hawaii shows that 12 of the 13 species in­ lau Range, Oahu. These species all have the vestigated are characterized by the diploid chro­ same chromosome number, and they flower at mosome number of n = 9, the chromosomes the same time over a considerable period of being of similar size. Thus there is a close time, so that the possibility of interspecific hy­ cytological affinity. The one exception to this bridizations should be given serious considera­ number is W. pulcherrima with the tetraploid tion. complement of n = 18. The latter species is restricted to a limited area on the island of ACKNOWLEDGMENTS Hawaii. It shows a close morphological affinity The support of the Watumull Foundation, with W. phillyreifolia, also restricted to that the Hawaiian Botanical Gardens Foundation, island, but more widely distributed. The two and the National Science Foundation is grate­ species resemble each other in all respects except fully acknowledged. Appreciation is extended that W. pulcherrima has larger flowers, fruit, to Dr. Bo Peterson, Botanical Museum, Uni­ and leaves. The stigma of W. pulcherrima is versity of Goteborg, for his review of the more capitate than that of W. phillyreifolia. manuscript. Thus it seems possible, from cytological evi­ dence (the presence of quadrivalents, aberrant LITERATURE CITED segregation, low pollen fertility) and morpho­ logical evidence, that W. pulcherrima could be CARLQUIST, S. 1966. The biota of long distance an autopolyploid race of W. phillyreifolia. dispersal. IV. Genetic Systems in the flora of Our observations show that the predominant Oceanic islands. Evolution, vol. 20, pp. 433­ breeding system in these species is a relatively 455. 88 PACIFIC SCIENCE, Vol. XXIII, January 1969

ENDLICHER, S. 1833. Prodromus Florae Nor­ Hawaiian Islands. II. Acta Horti Gothobur­ folkiceae. Fridericum Beck Universitatis Bib­ gensis, vol. 10, pp. 97-193. liopolam, Vindobonae. 47. --- 1944a. Vascular plants from the Ha­ FAGERLIND, F. YON. 1940. Zytologie und Ga­ waiian Islands. IV. Acta Horti Gothobur­ metophytenbildung in der Gattung Wik­ gensis, vol. 15, pp. 275-531. stroemia. Hereditas, vol. 26, pp. 1-50. --- 1944b. On the flower dimorphism in GRAY, A. 1865. New or little-known Polynesian Hawaiian Rubiaceae. Arkiv for botanik, vol. Thymeleae. Journal of Botany, vol. 3, pp. 31A, no. 4, pp. 1-28. 302-307. --- 1953. Chromosome numbers in Hawai­ HILLEBRAND, W. 1888. Flora of the Hawaiian ian flowering plants. Arkiv for botanik, ser. Islands. Heidelberg, Carl Winter. 673 pp. 2, vol. 3, pp. 63-70. HOD, DING. 1960. Thymelaeaceae. In: Flora ---(t). 1964. Wikstroemiae novae ha­ Malesiana, ser. 1, vol. 6, no. 1, pp. 28-35. waienses. Svensk botanisk Tidskrift, vol. 58, MEISNER, C. F. 1857. Thymelaeaceae. In: D. C. pp. 177-183. Prodromus XIV, pp. 543-548. SPARRE, B. 1964. Wikstroemia novae hawaiiensis OHWI, J. 1965. Flora of Japan. Washington, -a supplement. Svensk botanisk Tidskrift, D. c., The Smithsonian Institution. vol. 58, p. 497. ROCK, J. F. 1913. The indigenous trees of the WAWRA, F. H. YON. 1875. Beitrage zur Flora Hawaiian Islands. Honolulu, Hawaii. 518 pp. der Hawai'schen Inseln (Fortsetzung). Flora, SKOTTSBERG, C. 1936. Vascular plants from the vol. 58, pp. 184-192.