Native Plants of Hawai‘i - Rhus sandwicensis

Rhus sandwicensis

Anacardiaceae or Mango family [Wagner et al. 1990]; also known as the Cashew or Sumac family [Britannica]

Synonyms: Rhus chinensis var. sandwicensis, Rhus semialata var. sandwicensis

Neleau

Neneleau

Hawaiian sumac

Natural Range & Environment

Rhus sandwicensis is endemic to Kaua‘i, O‘ahu, Moloka‘i, Maui, and Hawai‘i Island from 150 to 750(–2,150) m (492 to 2,461(–7,054) ft). It is found in scattered wet-to-dry, disturbed areas, particularly along roadsides, in pastures [Wagner et al. 1990], and abandoned agricultural fields [J.B. Friday].

Given its hardiness and rapid growth, it is surprising that neleau is not more common in the Hawaiian Islands. It seems to be limited by some yet unidentified factor(s) to a few scattered locations throughout its range while being most common near Hilo and Waimea (Kamuela) on Hawaiʻi Island. It is found wild on Kaua‘i only on Makaweli and Kamaliʻi Ridge; on Oʻahu, only in Nuʻuanu and Moanalua Valleys and at Hoʻomaluhia; and on Molokaʻi, only in Pelekunu Valley [Flora of the Hawaiian Islands].

Neleau produces large inflorescences with many tiny yellow flowers (photograph courtesy of Forest & Kim Starr CC BY 3.0 US). When pollinated, each of these flowers develops into a drupe (fleshy single-seeded fruit) (photograph courtesy of Forest & Kim Starr CC BY 3.0). Neleau has large odd-pinnate compound leaves that are a striking red when young (red leaf photograph courtesy of Forest & Kim Starr CC BY 3.0). Neleau is deciduous, with its old leaves normally turning yellow to red and dropping sometime around the new year (photograph courtesy of Forest & Kim Starr CC BY 3.0). The attractive multi-colored stems of neleau are somewhat flexible but will break if bent too far (photograph courtesy of Daniel Barthelemy CC BY-SA 4.0).

A flowering neleau can be quite impressive (photograph courtesy of J.B. Friday ©) but can also attract a lot of bees. Because of its spreading nature, neleau is being planted on Hawai‘i Island where ‘ōhi‘a (Metrosideros polymorpha) have been killed by the fungal disease Rapid ‘Ōhi‘a Death in an attempt to prevent alien plants from invading and taking over these former native forests (photograph courtesy of J.B. Friday ©). Left on its own, neleau tends to spread via root suckers and form a dense thicket (photograph courtesy of Daniel Barthelemy CC BY-SA 4.0). However, with regular and proper pruning, it's possible to turn neleau into a proper shade tree (photograph courtesy of Forest & Kim Starr CC BY 2.0).

Description

Rhus sandwicensis is a small, long-lived (greater than five years) tree that produces numerous suckers from its spreading roots to form a dense thicket. It has light but durable wood and thin brown bark highlighted with many light-colored lenticels. A milky sap is exuded from any type of injury and is sometimes visible on its small fruits.

Neleau has large, odd-pinnate compound leaves with the lower surface typically lighter in color than the upper surface. The lance-like leaflets have serrated or toothed margins and a prominent network of veins visible on their lower surface. New leaves are a striking red, gradually turning green with age. Neleau is deciduous with old leaves turning yellow to red and then dropping typically around the new year.

Rhus sandwicensis has large inflorescences composed of many (hundreds?) tiny yellow 5-petaled flowers. Some, if not all, of the flowers are perfect (bisexual). However, given the number and density of flowers, there is some controversy as to whether some plants may have unisexual flowers, with even one report by Hillebrand & Hillebrand [1888] of the species being “apparently dioecious” (separate male and female plants). Blooms appear once a year during the late fall. Pollinated flowers develop into small round drupes (fleshy single-seeded fruits) that are reportedly edible [Little & Skolmen 1989]. Always be extremely cautious about eating any non-commercial fruit. Reportedly, these fruits turn red when ripe [Wagner et al. 1990]. However, I (Koebele) have only seen off-white fruits (see photograph above).

Growth Requirements

General

I (Koebele) am not sure why we so rarely see neleau in cultivation. Perhaps it’s misinformation from mainlanders who see neleau as a sumac and wrongly assume it must be poisonous. Well, it’s not! In fact, it’s harmless, and, although I’ve never eaten neleau fruits myself (and you too should always be cautious), they are reported to be edible [Little & Skolmen 1989]. Another possibility for neleau’s rarity in cultivation is its habit of producing numerous suckers from its roots and invasively spreading into areas of a landscape where it’s unwanted. While this is true, introduced plants like heliconias and gingers that also aggressively spread are extremely popular garden plants in Hawai‘i. Nor is neleau’s invasive spread inevitable. As you can see in the photograph above, it’s entirely possible to control the spread of neleau with regular pruning, so much so that you can actually turn your neleau into a shade tree. Therefore, neleau offers two primary landscape options: leave it to grow minimally pruned as a hedge or screen, or prune it consistently to create a tree.

Neleau does best in rainy places. And, while it’s possible to grow neleau in a dry-climate landscape with enough watering, it generally struggles in hot, dry places. The few times I have tried to grow neleau on the leeward side of O‘ahu, the plants consistently ended up with leaves that would brown and die along their margins; not an attractive look. Conversely, in cooler and rainier places like Hoʻomaluhia Botanical Garden on the windward side of Oahu, neleau grows like a weed [Honolulu Botanical Gardens].

In cloudy or rainy places, neleau does best when planted out in the open, while in mostly sunny areas, place your neleau in a bright but at least partially shaded site. While wild plants are occasionally seen in drier areas, you should keep the soil surrounding the roots of your neleau moist to wet at all times. Neleau doesn't seem particularly picky about soil type, provided it remains moist. I have grown it in rocky clay and organic-dominant soil; my potted plants were kept in a roughly half-and-half mix of sphagnum peat moss and black cinders. Based on my observations at Hoʻomaluhia Botanical Garden, O‘ahu, neleau seems able to survive brief periods in waterlogged soil.

Unfortunately, because of my limited attempts at growing neleau (in hot, leeward sites where it is not well suited), I cannot provide any estimates on its growth rate or age at first flowering. We welcome comments from anyone with either good and bad experiences growing neleau so we might improve the content of this page. Please contact us at EickhoffandKoebele@gmail.com.

Pests and Diseases

Neleau appears to have few pests; I've encountered none. However, when flowering, be mindful of the many bees that will visit your plant. Rock [1974 Reprint of 1913 book] noted that a large grove of neleau in Hilo died because of an (unidentified) fungus.

Uses

Ancient Hawaiian

Neleau may have been used “for plain calabashes, lomi lomi sticks” [Lennox 1967].

Modern

The light but tough wood of neleau was once used to make saddle trees (the internal frame over which a riding saddle is made), ox yokes and plows. Neleau bark was used in Hawai‘i for tanning goat skins [Little & Skolmen 1989]. More recently, neleau leaves have been used in cut floral arrangements.

While not often used, dying neleau leaves can be a colorful addition to a cut floral arrangement (photograph courtesy of Forest & Kim Starr CC BY 2.0).

Special Features and Information

General

Anacardiaceae contains about 870 species of trees, shrubs, and vines within about 80 genera, with most species native to tropical and subtropical regions of the Old and New Worlds. Several species are economically important nut and fruit crops, such as pistachio (Pistacia vera), cashew (Anacardium occidentale), and the locally popular mango (Mangifera indica). Not so popular and found outside Hawai‘i are poison ivy, poison oak, and poison sumac, all plants in the genus Toxicodendron [Britannica].

The endemic neleau is the only native member of Anacardiaceae in the Hawaiian Islands. Unlike some of its non-Hawaiian cousin species (e.g., poison sumac, native to North America), neleau is not poisonous, and its fruits are reportedly even edible [Little & Skolmen 1989], although I (Koebele) cannot comment on their flavor. In Hawai‘i, the introduced, naturalized, and highly invasive Christmas berry (Schinus terebinthifolia) is also a member of this family [Flora of the Hawaiian Islands].

Hawaiian Name

Etymology

Rhus is from an ancient Greek name for a sumac [Gledhill 2008]. The species name, sandwicensis, refers to the "Sandwich Islands," as the Hawaiian Islands were once called and named by James Cook on one of his voyages in the 1770s. James Cook named the islands to honor John Montagu (The fourth Earl of Sandwich) for supporting Cook's voyages [Gledhill 2008].

BPK