Acaena is a genus of about 60 species of mainly evergreen, creeping herbaceous perennial plants and subshrubs in the family Rosaceae, native mainly to the Southern Hemisphere, notably New Zealand, Australia and South America, but with a few species extending into the Northern Hemisphere, north to Hawaii (A. exigua) and California (A. pinnatifida).
The leaves are alternate, 4–15 centimetres (1.6–5.9 in) long, and pinnate or nearly so, with 7–21 leaflets. The flowers are produced in a tight globose [inflorescence] 1–2 centimetres (0.39–0.79 in) in diameter, with no petals. The fruit is also a dense ball of many seeds; in many (but not all) species the seeds bear a barbed arrowhead point, the seedhead forming a burr which attaches itself to animal fur or feathers for dispersal.
Several Acaena species in New Zealand are known by the common name bidibid. The word is written variously bidi-bidi, biddy-biddy, biddi-biddi, biddi-bid and a number of other variations. These names are the English rendition of the original Māori name of piripiri. The plant is also called the New Zealand burr. The species Acaena microphylla has gained the Royal Horticultural Society's Award of Garden Merit.
Etymology
The generic name Acaena is derived from the Greek "akaina" (thorn), referring to the spiny hypanthium.
Species
As of 2020, Plants of the World Online accepted the following species:
Acaena agnipila Gand.
Acaena alpina Poepp. ex Walp.
Acaena anserinifolia (J.R.Forst. & G.Forst.) J.B.Armstr.
Acaena antarctica Hook.f.
Acaena argentea Ruiz & Pav.
Acaena boliviana Gand.
Acaena buchananii Hook.f.
Acaena caesiiglauca (Bitter) Bergmans – glaucous pirri-pirri-bur
Acaena caespitosa Gillies ex Hook. & Arn.
Acaena confertissima Bitter
Acaena cylindristachya Ruiz & Pav.
Acaena dumicola B.H.Macmill. (South Island of New Zealand)
Acaena echinata Nees – sheep's burr
Acaena elongata L.
Acaena emittens B.H.Macmill. (North Island of New Zealand)
Acaena eupatoria Cham....
