Bidi-bidi – a corruption of the Maori name piripiri – is well known to all New Zealand children because of the hooked spines on the fruit of some species which attach themselves to clothing. They also stick to the fleece of sheep and thereby lower the quality of some wool from sheep feeding on dry, hilly pastures.
Acaena is a genus of mostly prostrate herbs belonging to the rose family. Its main centre of development is in the temperate mountains of South America. One species extends up into California. Others are found in Australia and Tasmania, and about 14, all of which are endemic, occur in New Zealand. There are approximately 150 species altogether, by far the greater number being found in South America.
A. novae-zelandiae, probably the commonest species, is found throughout the country at the lower elevations, in tussock grassland, and open places. This plant has woody, creeping and rooting stems up to 3 ft long with short, ascending branches. The leaves are pinnate, with a dozen or more leaflets, and are up to 3 in. long. Flowers are in rounded heads on stalks about 3 in. long. The dark purple spines on the fruits stick out somewhat less than half an inch all around the head. Another widespread species is A. anserinifolia which has much the same distribution as the above. The spines are yellowish green to dark-brown. A very beautiful little plant is A. microphylla which forms mats in open places and in low vegetation about the volcanic plateau in the North Island and mainly to the east of the Southern Alps in the South Island. The spines are crimson or in shades of red and have no hooks. A. buchananii found in the South Island has yellow spines. Hybrids occur between some New Zealand species, and between the Australian, A. ovina and A. anserinifolia. These are common wherever the two species meet. A. ovina and A. novae-zelandiae also hybridise freely.
by Alec Lindsay Poole, M.SC., B.FOR.SC., F.R.S.N.Z., Director-General of Forests, Wellington.