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Description: The botanical genus name of Dodonaea honors the Flemish Royal Physician, botanist and professor, Rembert Dodoens, while the specific name (epithet) of viscosa is derived from the Latin term viscosus, referring to the sticky exudate produced the leaves of this species. Although this species often occurs as a shrub growing up to 1–3 m (3–9 ft) tall, but more rarely develops into a small tree up to 9 m (about 30 ft) tall. The leaves are variable in shape, but generally are obovate; but some are lanceolate, often sessile, with a pointed or rounded apex; they are 4–7.5 cm (1.6–3.0 in) long and 1–1.5 cm (0.39–0.59 in) wide, and are alternately arranged along the stems. The leaves secrete a resinous substance and have a texture that is leathery and tough, but also pliable and usually gives them a recently varnished appearance. The leaves of D. viscosa generally have conspicuous veins and their edges may be weakly toothed (serrated) or undulating. The distinctive flowers are yellow to orange-red and produced in panicles about 2.5 cm (1 in) in length. The flowers are only male or female, and one plant normally bears only male or female flowers (under such circumstances it is therefore dioceous). However, sometimes individuals of D. viscosa do bear flowers of both sexes. The pollen of D. viscosa is transported by the wind (a process known as anemophily). It is believed that during its evolution, D. viscosa developed flowers lacking petals to increase exposure to the wind for pollen dispersal. The female flowers, after pollination, develop into 3 or 4 winged papery capsules, each with 2-3 black lenticular seeds about 2-3 mm long. The attractive seed capsules turn red or purple as the fruit matures.
Distribution: Dodonaea viscosa is a woody, flowering species in the soapberry family, Sapindaceae, and has a very wide cosmopolitan distribution in tropical, subtropical, and warm temperate regions of the Pacific, Australia, New Zealand, South and Southeast Asia, Africa and Latin America; also occurring in the southern United States. The small lenticular seeds of D. viscosa “do not immediately suggest the likelihood of an intercontinental distribution, yet the species occurs in every subtropical and tropical region” of the world (see Prendergast and Pearman 2001:184). D. viscosa was described by the global phytogeographer Good (1974) as a very widespread tropical weed also found widely as a “strand plant,” growing in nearly all tropical coastal environement with appropriate soil conditions. More than a century ago, Guppy (1906) had noted that “few strand plants are not somewhere or other found growing naturally inland,” and D. viscosa is definitely one of these species. The probable explanation for the very widespread natural distribution of D. viscosa is its pronounced seed dormancy due to its water-impermeable seed coat (Baskin et al. 2004:81). D. viscosa easily occupies exposed areas and secondary forest in well-drained soil; it is also resistant to salinity, drought and pollution and therefore is able to grow in coastal environments. A key characteristic of of its hardiness, especially in dry, exposed areas is the relatively deep tap root that it develops. Although it is often found in rocky places and in open waste ground in patches, it is intolerant of frost and does not grow well in shade.
General Uses: Hopbush or Sticky Hopbush (Dodonaea viscosa) is a highly variable evergreen shrub or small tree with several subspecies and varieties. It is a very widespread species and its numerous useful properties have been discovered independently by people of different continents. D. viscosa readily colonizes open areas and secondary forest, and is tolerant of salinity, drought and pollution. It is therefore useful for dune stabilization, restoring degraded lands and for reforestation. The flowers are relatively unspectacular, but its winged fruits can become red or purple as they mature, making it an attractive garden plant in the tropics and subtropics. One cultivated variety also develops purple leaves when grown in direct light. Indeed, its fast growth and tolerance of strong winds make it an excellent hedge and windbreak, and it is planted as a decorative shrub (e.g. in South Africa, Australia and southern U.S.A.). Furthermore, developing hedges of D. viscosa is made somewhat easier because it can be reproduced from cuttings which will, more or less, ensure that the resulting plants have the same desirable characteristics as the parent plant; However, D. viscosa plants are reportedly difficult to transplant when they are more than 60 cm (~24 in) tall. Early settlers in Australia used D. viscosa as a substitute for hops for brewing beer (as reflected in some of common names of this plant); this hops substitute use is also recorded from Iraq. In addition, D. viscosa is considered a valuable source of pollen by apiculturalists (e.g., see Clemson 1985), and its leaves have been reported to be chewed as a stimulant in some parts of the world (e.g. in Colombia and Peru, where the leaves are sometimes mixed with coca, Erythroxylum coca). The wood of D. viscosa is very sturdy and durable. In New Zealand (Aotearoa), where D. viscosa (Akeake) produces the heaviest native wood, the indigenous people have traditionally used it to make weapons, carved walking sticks, axe-handles, and weights for drill shafts. Native Hawaiian people used D. viscosa (‘aʻaliʻi) to make house posts, fishing lures, digging sticks for its wood and a reddish dye from the fruit. (e.g., see Felger and Moser 1985). In the past D. viscosa was used instead of hops for beer brewing by Australians (as reflected in the name “hopbush”), and in some areas of New Guinea, people use it as incense for funerals. Furthermore, D. viscosa is also known to have been used by the people from the western part of the island of New Guinea, Southeast Asia, West Africa and Brazil for house building and as firewood, while its leaves may also be used medicinally such as for wound plasters.
Medicinal Uses of Dodonaea viscosa: The extensive review of Pearman (2000) of enthnobotanical aspects of D. viscosa in 40 countries from which human use data were available revealed that “the most frequently recorded use of D. viscosa (174 records; 50% of total) was as a medicinal, either as the lead property or not” (e.g., the Seri people of the dry Southwestern Mexico reportedly use this plant for medicine; and it also said to have been used in some areas of Africa and Asia “to stimulate lactation in mothers, as a dysentery treatment, to cure digestive system disorders, skin problems and rheumatism” (see Pearman, 2000, and Prendergast and Pearman, 2001, for more details regarding the very widespread, varied medicinal and material use of D. viscosa). More recently, Rani et al. (2009:99) summed up the global herbal therapeutic value of this species:
“Dodonaea viscosa has many medicinal properties and has been used by native peoples from all regions where it is found. It is a traditional medicine worldwide, administered orally or as poultice to treat a great variety of ailments.”
For an overview of the ethnopharmacology of Dodonaea viscosa see Wiart (2006:173-174) and Pujar (2012, who deals with the “flavonoid rich plant and its biological potential” of D. viscosa).
Uses by Island or Island Group: Balick (2014:40) listed Dodonaea viscosa as among the “Important Herbs of Oceania” and referred an example of its medicinal uses as a “Toothache and insect sting remedy.”
Uses in Palau: The leaves of Dodonaea viscosa, known in Palau as Mesechelangel (or Masikirangl), have reportedly been used medicinally to reduce fever in Palau (Wiart 2006:172).
Uses in Yap: Dodonaea viscosa, known in Yap as Goichap, apparently has been used for medicinal purposes in these Caroline Islands. For example, in the Map District of Yap, Okabe (see Defilipps 1988:21) reported that liquid “oozing from the crumpled leaves [of D. viscosa] is applied to a wound.”
Uses in the Mariana Islands: Dodonaea viscosa, known in the Mariana Islands as Lampuaye or Lampuayi, is, according to Stone (1970:396-397), generally found on Guam “in the southern savannahs, where it is not uncommon, appearing usually as a small bush about 1-2m tall,” and although the “wood is said to be very hard,” not many “plants attain a suitable size for use.” On the other hand, D. viscosa has reportedly been used for medicinal and other practical purposes in these islands. For example, according to Safford (1905:264), the leaves of D. viscosa “have a sour-bitter taste and said to have febrifugal [fever relieving] properties,” is a good choice for planting “hedges,” and its wood is used for fuel because it “ignites readily.” Interestingly, some botanists, agriculturalists and foresters believe that Dodonaea viscosa is not indigenous, but rather a “naturalized species in the Mariana Islands” (e.g., https://www.flickr.com/photos/jbfriday/40355814480). D. viscosa is definitely a pioneer woody species common in secondary vegetation areas such as those that occur in the Northern Mariana Islands, e.g., Saipan, Rota and Tinian (e.g., Falanruw et al. 1989), and even occasionally occurs near the coast in coastal scrub vegetation such as on Saipan Island as reported by Raulerson and Rinehart (1989:4). Kessler (2002:138-139), in his discussion of the eradication of feral goats and pigs and consequences for other biota on Sarigan Island in the the Northern Mariana Islands, referred to the reforestation role of D. viscosa:
“In the Marianas, it seems that goats and pigs are a destructive force capable of changing the microclimate of the forest floor… [However the removal of ungulates, or hoofed mammals, in these islands] has stopped and reversed the process of forest loss and has re-established the forest floor microclimate (in less than a year). Likewise, the native forest is expanding and regenerating. Many new trees were observed growing in areas that were previously grassland; the sudden eruption of new growth has undoubtedly slowed erosion and contributes to new soil being laid down. The general trend appears to be the changing of grassland to forest. Areas of Chrysopogon acicularis grassland and bare dirt are sprouting new thickets of the shrubby species Dodonaea viscosa.”
Uses in Kiribati: D. viscosa is known in Kiribati as “te kaiboia” which literally means “smelly plant” (Thaman 1990:28). The fruits of D. viscosa are used in the atolls of Kiribati in garlands or and the young leaves are used to perfume coconut oil, while its durable stems are used as sturdy fishing poles as wells as for the frames of fishing dip nets (Catala 1957:92). Although this species, listed as “native hop bush” by Thaman (1987:28), is said to be indigenous to many tropical Pacific islands, it may not be native to Kiribati, e.g., according to “Overy, et. al., (1982:65), Dodonea viscosa is thought to have been introduced about 1945” (Thaman 1987:9). In any case, in recent times, it is “locally common near existing villages and in sites of former dwellings and occasional in garden areas” and, as noted above, it does have a number of local uses; indeed, Clarke and Thaman (1993), in their discussion of traditional agriculture on Tarawa and Abemama Atolls in Kiribati, included D. viscosa as one of the significant “indigenous trees or tree-like species, which are integral and widespread components of the Kiribati agroforestry system.” Clarke and Thaman (1993) based this assessment on field surveys and the published research of Luomala (1953), Catala (1957), Moul (1957), and Overy et al. (1982).
Uses in Nauru: D. viscosa, known Eteweo or Eteweau on Nauru (Thaman 1987:6), is commonly found in the scrub vegetation and occasionally occurs in the plateau forest of Nauru as well as in older mined areas that are revegetated: “Strong but flexible trunks and branches [are] used for fishing rods and for frames for flying-fish and noddy nets; leaves [are] occasionally used to scent coconut oil” (Thaman et al. 1994:193).