Pittosporum crassifolium, commonly called karo, is a small tree or shrub native to New Zealand. Karo's original distribution was generally the top half of the North Island, although now it has naturalised throughout New Zealand and overseas in Norfolk Island and Hawaii. P. crassifolium occurs in lowland and coastal forests. Mature trees grow to about 5 metres (16 ft) in height. Other common names include stiffleaf cheesewood, and in Māori, kaikaro and kīhihi.
Karo has dense dark gray-green leathery leaves that are furry underneath. An early coloniser, P. crassifolium is able to withstand high winds and salt spray. Clusters of small red-purple flowers appear in spring, developing into seed pods that split to expose the sticky seeds.
Pittosporum crassifolium is considered to be "weeds in cultivation" in California. They are being kept under observation to ensure they do not escape into the wild. In New Zealand birds easily spread karo seed and in areas south of its natural range it has become a pest plant.
- "Pittosporum crassifolium". New Zealand Plant Conservation Network. Retrieved 28 May 2012.
- "Karo, kaikaro, tarata, kōhūhū, koihu". Maori uses: Medicinal plants, Trees & Shrubs. University of Auckland.
- Harris, Graeme (June 2002). "Our Native Plant Invaders". The New Zealand Garden Journal. Royal New Zealand Institute of Horticulture. 5 (1): 6–8.
- "Story: Shrubs and small trees of the forest - Karo". Te Ara - the Encyclopedia of New Zealand. Retrieved 28 May 2012.
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