Homalium  (Homalium taypau)

Classified as Vulnerable (VU) on the IUCN Red List (1).

Homalium taypau is a medium-sized, low-branched tree of the willow family that is endemic to Pitcairn Island in the southern Pacific Ocean (3). This deciduous tree has small purple flowers that are arranged in large, compact, elongated clusters known as catkins, with each flower suspended from a tiny stalk and possessing small, inconspicuous petals. The individual flowers branch from the stem at right angles and are each accompanied by a bract. The leaves of Homalium taypau have a slight swelling at the base and have minute hairs. The buds are scaly in appearance (4).

Homalium taypau is endemic to Pitcairn Island in the southern Pacific Ocean (1) (5).

Homalium taypau grows on forested hillsides and valleys with a dense under-layer of native ferns, with pure stands of the species found in less disturbed parts of Pitcairn Island (3) (6).

Very little is known about the biology of Homalium taypau, but like other members of the willow family it is dioecious, meaning the male and female flowers are borne on separate plants. The flowers also produce nectar and are pollinated by insects, and the seeds are scattered by the wind (4).

Despite being of relatively low diversity, the plant communities on Pitcairn Island have a high proportion of threatened species and a number of endemics (1) (7). Habitat loss and competition for natural resources with exotic species are threatening the survival of much of the native flora (7). These threats began soon after the arrival of early settlers on the island, with lowland forests cleared for construction, agriculture and firewood. Exotic species were introduced to the island, sometimes deliberately, and cultivated plants established in the wild (8). On such species, the fruit tree Syzygium jambos¸ was initially introduced to provide firewood, but now that it is rarely used for this purpose, the species is spreading rapidly across the island and threatening much of the native flora (3) (8). Today around half of the Pitcairn flora is threatened with extinction, with less than 30 percent of the island covered in natural vegetation (6). 

Homalium taypau was once harvested for its timber for use in construction work and, consequently, this exploitation has divided the population into fragments across the island. It is still common in places, and tends to dominate the forests in undisturbed lowland valleys, and at least 2,000 individual trees were remaining in 1998 (1) (5). However, habitat loss and competition with exotic species continue to threaten this Vulnerable tree, and these threats are compounded by the difficulty in propagating the species from seedlings (1) (6) (9).

The most urgent conservation requirements for Pitcairn’s plants are the clearance of invasive species, tackling habitat loss and the establishment of ex-situ conservation measures for some of the island’s most threatened floral species (6) (7). Efforts are already underway to remove exotic species, and Syzygium jambos is being controlled by making cuts into the tree’s trunk and injecting poisonous chemicals to kill it. It is also thought that much of the island’s threatened plants could be protected by the establishment of a system of reserves, and the replanting of native plants after the clearance of exotic species (6) (9). These measures, however, will only be successful with the support and involvement of the islands small, yet significant human population (6) (8).

ARKive is supported by OTEP, a joint programme of funding from the UK FCO and DFID which provides support to address priority environmental issues in the Overseas Territories, and Defra

For more information on tree conservation, see:

• The Global Trees Campaign: 
  http://www.globaltrees.org/

To find out more about conservation on Pitcairn Island, see:

• Procter, D. and Fleming, L.V. (1999) Biodiversity: the UK Overseas Territories. Joint Nature Conservation Committee, Peterborough, UK.
• National Botanic Gardens, Glasnevin:
  http://www.botanicgardens.ie/herb/pitcairn.htm