Colin Varndell / Pirri-pirri-bur (Acaena novae-zelandiae) Studland Heath National Nature Reserve, June. Introduced species.

Adrian Davies / Pirri pirri bur (Acaena novaezelandiae) UK. Invasive species native to Australia and New Zealand.

Adrian Davies / Pirri pirri bur (Acaena novaezelandiae) UK. Invasive species native to Australia and New Zealand.

Ingo Arndt / Greater Burnet (Acaena magellanica) Cumberland East Bay, South Georgia Island, February

Richard Robinson / Northern giant petrel (Macronectes halli) chick sits upon a bed of Acaena minor (var. antarctica) a prostrate dicotyledonous herb at Enderby Island in the subantarctic Auckland Islands archipelago, Ne...

Colin Varndell / Pirri-pirri bur (Acaena novae-zelandiae) seed heads. Studland Heath, Dorset, UK, June. Invasive species.

Colin Varndell / Pirri-pirri-bur (Acaena novae zelandiae) in flower. Studland Heath National Nature Reserve, June.

Colin Varndell / Pirri-pirri-bur (Acaena novae zelandiae) in flower. Studland Heath NNR, Dorset, UK. June.

Paul Hobson / Bronze Piri piri bur (Acaena novae zelandiae) close-up of two seedheads, Lindesfarne, UK, July

Ingo Arndt / Acaena (Acaena sp) flowers, Torres del Paine National Park, Patagonia, Chile

Dave Watts / Biddy biddy (Acaena novae-zelandiae). Tasmania, Australia. December.

Ernie Janes / Piri piri burr (Acaena novae-zelandiae) invasive species, Suffolk, England, UK, August.