Native Plants of Hawai‘i - Pittosporum glabrum

Pittosporum glabrum

Pittosporaceae or Pittosporum family

Synonyms: Pittosporum acuminatum, Pittosporum acuminatum var. degeneri, Pittosporum acuminatum var. leptopodum, Pittosporum acuminatum var. magnifolium, Pittosporum acuminatum var. waimeanum, Pittosporum acutisepalum, Pittosporum dolosum, Pittosporum dolosum var. aquilonium, Pittosporum fauriei, Pittosporum glabrum var. glomeratum, Pittosporum glabrum f. hypoleium, Pittosporum glabrum var. intermedium, Pittosporum glabrum var. spathulatum, Pittosporum glabrum f. subcandidum, Pittosporum glabrum var. tinifolium, Pittosporum glomeratum, Pittosporum glomeratum var. acutisepala, Pittosporum helleri, Pittosporum hillebrandii, Pittosporum insigne, Pittosporum insigne var. fosbergii, Pittosporum insigne var. hillebrandii, Pittosporum insigne var. lydgatei, Pittosporum insigne var. micranthum, Pittosporum insigne var. pelekunuanum, Pittosporum kahananum, Pittosporum spathulatum, Pittosporum sulcatum, Pittosporum sulcatum var. remyi, Pittosporum sulcatum var. rumicifolium, Pittosporum sulcatum f. tomentellum, Pittosporum terminalioides var. glabrum

Hōʻawa

Hāʻawa, Papahekili

Koʻolau Range cheesewood

Natural Range & Environment

Pittosporum glabrum is endemic to Kaua‘i, O‘ahu, Moloka‘i, Lāna‘i, and Maui, and is the most common and widespread of the Hawaiian Pittosporum. It is found in mesic to wet forests and on the margins of bogs from 240 to 1,970 m (787 to 6,463 ft) [Wagner et al. 1990].

Pittosporum glabrum produces clusters of unisexual (male and female) flowers near the stem-tips or lower down along the branch (Flower photograph here and in header courtesy of Forest & Kim Starr CC BY 3.0.). An interesting photograph (courtesy of Forest & Kim Starr CC BY 3.0 US) of pollinated female flowers with enlarging ovaries but still retaining now-dead petals. Hōʻawa has hard walnut-like fruits that split open when ripe to reveal their sticky black seeds, supposedly a favored food of the endangered ʻalalā or Hawaiian crow (Corvus hawaiiensis). Both the upper and lower surfaces of mature P. glabrum leaves are hairless, hence the species name, glabrum. A mature cultivated P. glabrum doing quite well in the hot dry lowlands of O‘ahu with very little watering.

Description

Pittosporum glabrum is a shrub to small tree up to 26 feet (8 m) tall [Wagner et al. 1990] with a lifespan much longer than five years. It has thick obovate to spoon-like leaves with a rolled margin and slightly impressed veins on the upper surface and slightly raised veins on the underside. Leave size can vary a lot, from 2 to 9 inches (5 to 23 cm) long. New leaves are typically covered in pale brown hairs but become hairless (or nearly so) on both their upper and lower surfaces as they mature, hence the species name glabrum.

Pittosporum glabrum produces clusters of small cup-shaped 5-petal white to cream-colored unisexual (male and female) flowers near the tip of the stem but also lower down along the branch. In our experience with cultivated plants, a single plant will have both male and female flowers. The flowers have a weakly sweet scent, particularly at night. Cultivated plants bloom sporadically year round.

Hōʻawa capsules (i.e., fruits), which look a lot like walnuts, develop and mature slowly, turning from green to dark brown or black when ripe. They then split open, without any warning (as far as we can tell), to reveal their bright yellow to red, most often orange, interior packed with a few dozen viscous black angled seeds. The outer surface of Pittosporum glabrum capsules are usually smoother than those of some other hōʻawa species such as P. confertiflorum. Be aware that Hawaiian Pittosporum can hybridize [Bacon et al. 2011], and, therefore, you should follow a strict protocol if you intend to grow new plants from collected seeds; see Pritchardia martii for how to do this.

Growth Requirements

General

Pittosporum glabrum, with its leathery leaves and curious walnut-like fruits, is a great addition to any landscape. Use it as an accent or, planted several feet apart, as an informal (i.e., very lightly pruned) screen or hedge. The deep shade it produces can provide habitat underneath for sun-sensitive plants like ferns. It can also be kept as a container plant; however, if not periodically transferred to a larger container, hōʻawa will become potbound and stunted.

In the wild, the environmental range of Pittosporum glabrum is not as wide as P. confertiflorum; P. glabrum seems to be more common in wetter habitats. However, in cultivation, the two species have very similar (identical?) growth requirements, and like P. confertiflorum, P. glabrum can be successfully grown at much lower elevations (i.e., hotter and drier) than its natural range.

Hōʻawa grows well both in a site with full sunlight all or most of the day, as well as a partially or lightly shaded location, provided it receives enough water. Watering will require a bit of experimentation on your part, depending on how much rainfall, sunlight, heat, and wind your hōʻawa is exposed to. Generally, you should try to keep the surface soil dry most of the time and the subsurface (one or two inches down) soil moist all of the time. While hōʻawa can endure brief periods of drought, never let the soil around your hōʻawa become bone dry.

Leland Miyano, a local landscape architect and artist, who has probably grown more hōʻawa than anyone, recommends disturbing a hōʻawa's roots as little as possible when planting it in the ground or transferring it to a new pot. Hōʻawa will grow in lava/cinder, clay, and organic-dominant soils, as long as the soil drains water well. We have not tried to grow hōʻawa in sandy or coralline soils.

Hōʻawa tends to grow in spurts at a slow to moderate pace, putting out whorls of new leaves rather than one leaf at a time. Under optimum conditions, expect your plant to grow about a foot (30 cm) taller each year and begin flowering after about five years. Prune it only to remove dead branches. Again, be aware that Hawaiian Pittosporum can hybridize [Bacon et al. 2011], and, therefore, you should follow a strict protocol if you intend to grow new plants from collected seeds; see Pritchardia martii for how to do this.

Pests and Diseases

Hōʻawa are prone to scale insect infestations, often farmed and protected by ants, and spider mites (look for them on the undersurface of the leaves). Less often, other sap-sucking pests such as aphids and mealybugs will attack hōʻawa. The honeydew produced by these pests often results in a sooty mold growing on the leaves and stems. Refer to the Pests & Diseases page for ways to battle each of these pests.

Uses

Ancient Hawaiian

There are currently (2025) 11 native species of Pittosporum in Hawai‘i, all with the shared Hawaiian name, hōʻawa, although some species have one or two additional Hawaiian names. Because of this commonality, it was impossible for us to determine if a documented use was valid for all Hawaiian Pittosporum species or just some or one. Therefore, the uses described below are those we were able to find in the literature for all (unspecified) "hōʻawa."

Hōʻawa wood was used to make the gunwales of canoes [Krauss 1993]. Hawaiians also supposedly used the outer layer of hōʻawa fruit valves by pounding them up and applying them externally to sores [Neal 1965]. Ka‘aiakamanu & Akina [1922] describe a somewhat similar use to that described by Neal [1965] for a "scrofulous swelling about the neck," but the treatment includes other plants pounded along with the "meat" of hōʻawa fruits. Ka‘aiakamanu [2003] also describes Hawaiians with "priestly knowledge" using hōʻawa to "bathe someone who is thought to be sick or perhaps visited by ghost."

Modern

Special Features and Information

General

Pittosporaceae is a small family of about 240 species within nine genera that are limited to tropical and temperate Africa, Australia, Indo-Malaysia, and Oceania, with the majority of species in the genus Pittosporum [WikipediA;Pittosporaceae].

In Hawai‘i, there are 11 native Pittosporum species, all endemic, with P. glabrum being the most widespread and common [Flora of the Hawaiian Islands].

Rock [1974] noted that the endemic (and now critically endangered) ʻalalā (Corvus hawaiiensis; Hawaiian crow), which was still very common in the 1910s, would peck at the capsules of Pittosporum hosmeri, a hōʻawa endemic to Hawai‘i Island, and eat the oily seeds inside.

Hawaiian Name

Etymology

Pittosporum is derived from the Greek words, pitta, meaning "tar" or "pitch," and sporos, meaning "seed," referring to the sticky film of resin covering the seeds [Gledhill 2008]. The species name, glabrum, is Latin for "hairless, smooth" [Latdict], referring to the mature leaves of this species generally being hairless.

BPK