The Hawaiian tree fern is native to most of the Hawaiian Islands. Although once common, hapu’u stands have been reduced due to a large number of ferns being harvested for orchid media and landscape use. The last remaining large stands of native hapu’u are found on the Big Island.
The Hawaiian hapu’u are very slow growing; the young ones grow at about 3.5 inches per year while the older plants grow even more slowly, eventually growing to 15-20 feet tall. The unfurled fronds are covered with silky, red-brown wool-like fibers called pulu. In the past, pulu was used for stuffing pillows and mattresses and for dressing wounds.
The Hawaiian tree ferns are relatively easy to grow. They grow best in well drained slightly acid soils and partial shade; they will tolerate full sun in cloudy upland areas. They need a steady supply of water and occasional light applications of a complete, slow release fertilizer. Old and injured fronds should be pruned. It is illegal to ship tree ferns or products from the ferns internationally.
The Australian tree fern, Cyathea cooperi, is considered invasive in the State of Hawaii due to aggressively out competing native plants in the forest understory. As a threat to Hawaiian forests, this fern eventually displaces the native ferns, including the slower growing Hawaiian tree fern, or hapu’u.
Although invasive, the Australian tree fern is being sold in Hawaii at many commercial plant nurseries. This fern grows to 40 feet tall and tolerates full sun in cool wet areas. The spores are spread by wind and can travel over 7 miles from the parent plant.
The best diagnostic characteristic to distinguish between the Australian tree fern and the native hapu'u is the hairs on the leaf stems. With the hapu’u, the hairs are either fine and reddish-brown for hapu'u pulu (Cibotium glaucum) or fine and black for hapu'u i'i (C. menziesii). The hairs on the Australian tree fern are broad and white.
Photos: Native Plants Hawaii, University of Hawaii