Acaena species - Pirri-pirri-burs

There are four species of these aliens from New Zealand and Australia. They escape from gardens and can easily be established and spread due to the spines attached to the seeds. So they can be found where garden waste is discarded but also alongside forestry tracks well away from houses.

The crucial distinguishing features are the shape of the last pair of leaflets, the number of teeth (count round the leaf including both sides) and the colour and shininess of the leaves. The commonest are Acaena novae-zelandiae and especially Acaena ovalifolia.

Acaena anserinifolia, Bronze Pirri-pirri-bur, has bronze-tinged matt foliage. The last pair of leaflets have 5 – 12 teeth and are 1.2 – 2 times as long as wide. There are up to 4 spines on each part of the seed head.

Acaena inermis, Spineless Acaena, has no spines on the seed heads. (photos to follow)

Acaena novae-zelandiae Pirri-pirri-bur, has glossy green foliage. The last pair of leaflets have 5 – 12 teeth and are 1.8 – 2.5 times as long as wide. (photos to follow)

Acaena ovalifolia, Two-spined Acaena. Here, the last pair of leaflets have 17 - 23 teeth and are 1.7 – 2 times as long as wide. There are up to 2 spines on each part of the seed head.