Pittosporum Gaertn. is a genus of roughly 250 to 350 flowering shrubs and small trees in the family Pittosporaceae (order Apiales). The genus name comes from the Greek words for "pitch" or "tar" (πίττα, pitta) and "seed" (σπόρος, sporos), a direct reference to the sticky viscid resin that surrounds the seeds inside the fruit — a characteristic that sets the genus apart at a glance.
Plants are generally evergreen shrubs or small trees, occasionally with spiny stems, bearing simple leaves arranged alternately along the branches. The flowers range from white to yellow, with petals fused at the base, and are frequently fragrant. The fruit is a woody or leathery capsule that splits at maturity to reveal seeds coated in that distinctive resinous fluid. In English-speaking countries the genus is most commonly known as cheesewood, though Hawaiian speakers use the name hōʻawa and German speakers know it as Klebsamen ("sticky seed").
The genus has a remarkably wide native distribution spanning southern Africa and Madagascar, through the Arabian Peninsula (Saudi Arabia, Yemen), the Indian subcontinent, China, Korea, Japan, and Southeast Asia, continuing into New Guinea, Australia, New Zealand, and across the Pacific Islands. This breadth makes Pittosporum one of the more geographically diverse genera in its family, with representation in both tropical and temperate floras. Several species are well-established ornamentals in cultivation worldwide; a few, notably P. undulatum, have naturalized and become invasive beyond their native range.
Etymology
The genus name Pittosporum was coined by Joseph Gaertner in his 1788 work De Fructibus et Seminibus Plantarum, building on an unpublished description by the botanist Joseph Banks. Gaertner formed the name from two Greek roots: πίττα (pitta), meaning "pitch" or "tar," and σπόρος (sporos), meaning "seed." The compound name thus means something like "pitch-seed" or "tarry seed," directly describing the thick, resinous, viscid fluid that coats the seeds within the ripe capsule. This same trait accounts for the German vernacular Klebsamen ("sticky seed") and underlies the French name pittospore.
Distribution
Pittosporum has one of the widest native ranges of any genus in Pittosporaceae, spanning three major continents and numerous island groups. The core of its native distribution covers sub-Saharan Africa and Madagascar in the west, through the Arabian Peninsula (Saudi Arabia, Yemen), the Indian subcontinent, China, Korea, and Japan, then through Southeast Asia and New Guinea to Australia, New Zealand, and the Pacific Islands.
Within China alone the genus is represented by numerous species concentrated in the south and southwest (Guangdong, Guangxi, Hainan). In New Zealand the genus includes ecologically important native trees such as P. tenuifolium and P. eugenioides. Australia has a substantial contingent of endemic species, particularly in eastern and tropical regions.
In cultivation, several species have naturalized outside their native range. P. tobira from East Asia is established as a neophyte in parts of Europe, including Switzerland, where it was added to the national neophyte checklist in 2017.
Ecology
Members of Pittosporum occupy a broad range of habitats consistent with their wide geographic distribution. Species found in Asia typically grow in forests, thickets, and along river banks and stream sides, often at mid-to-high elevations (recorded at 1500–1800 m in southern China). The genus includes both canopy and understory elements in subtropical and warm-temperate forests.
Several species produce seeds with a viscid coating that facilitates dispersal by birds — the sticky coating adheres to beaks and feet. This adaptation contributes to the successful naturalization of opportunistic species such as P. undulatum in disturbed habitats outside its native range.
Cultivation
Pittosporum species are widely grown as ornamental shrubs and hedging plants in temperate and subtropical gardens. They tolerate a range of soil types — light sandy soils, loamy soils, and heavier clay soils — and perform across mildly acid to basic pH. Most species accept full sun or partial shade, and established plants are reasonably drought-tolerant once established, though they also perform well in moist situations.
P. tobira, the most widely cultivated species, is a popular hedging and foundation plant across the Mediterranean, Pacific Coast of North America, and mild-temperate regions of Europe. P. tenuifolium from New Zealand is a common hedging plant in the UK and Ireland, valued for its dark stems and undulating leaf margins.
Propagation
Pittosporum can be propagated by seed or vegetative cuttings. Seeds are best sown in autumn or late winter in a warm greenhouse; germination is generally reliable. Vegetative propagation via semi-ripe (half-ripe) heel cuttings of 5–7 cm taken in July or August is the standard commercial method, though success rates are moderate rather than high. For named cultivars and variegated forms, cuttings are the preferred method to maintain true-to-type plants.
Taxonomy notes
Pittosporum Gaertn. (1788) is the type genus of the family Pittosporaceae and is placed in the order Apiales. The genus is nomenclaturally conserved (Nom. cons.) as recorded by GBIF. Gaertner formally established it in 1788 based on material that Joseph Banks had collected and described but never formally published.
GBIF records 347 descendant taxa for the genus. Earlier estimates cited approximately 250 species, and circumscription continues to evolve as regional revisions reassess species boundaries, particularly in New Caledonia (rich in endemics), Hawaii, and sub-Saharan Africa. Some members of the genus contain saponins.
