Spectacular comeback for Chatham Island Sow-thistle

Chatham Island sow thistle in flower. Image: Peter de LangeChatham Island sow thistle in flower. Image: Peter de LangeThe Chatham Islands Sow-thistle or Embergeria grandifoliais one of two endemic plant genera known only from the Chatham Islands. For most of the last fifty years the sow-thistle has been in decline throughout the Chatham Islands such that at one time it was ranked by the International Union for the Conservation of Nature (IUCN) as "Endangered" meaning that if the decline wasn't halted it would soon go extinct.

Since the late 1990s the Department of Conservation in cooperation with Chatham Islanders has been working to save this peculiar plant from extinction. While Chatham Island sow-thistle is probably not the most attractive looking of plants it is undoubtedly of world wide interest. Superficially resembling the introduced puwha/sow-thistles (Sonchus spp.), the Chatham Islands Sow-thistle is a much larger plant with flowering specimens sometimes reaching up to 1.8 m in height. The yellow-green leaves are very leathery and can be up to 1 m long, while the dense clusters of daisy-like flowers are produced in profusion and multi-coloured in shades of yellow, apricot and purple.

Chatham Island sow thistle foliage infected with Embergeria Rust. Image: Peter de LangeChatham Island sow thistle foliage infected with Embergeria Rust. Image: Peter de LangeWhile some botanists have opined that Embergeria grandifolia is nothing but a large island form of puwha, and should not be regarded in its own unique genus, recent DNA studies have shown that it is not that closely related to puwha but shares a distant ancestry with an Australian daisy (Actites megalocarpus) and another plant peculiar to New Zealand, a small dandelion like herb called Kirkianella. The plant is also special because it supports its own unique rust. While having your own unique disease may not sound that desirable it is important to appreciate that conservation management is about protecting diversity. The so called Embergeria Rust (Puccinia embergeriae) is one of the most threatened fungi in the world, being so far known on only five wild plants of Chatham Islands Sow-thistle (all growing at Kaingaroa). Clearly any conservation management would need to consider saving the rust as well as its threatened host plant.

The past decline of the Chatham Islands sow-thistle can be directly attributed to the uncontrolled spread of browsing animals and habitat deterioration on the main islands of the Chatham group. By the 1980's few populations were left on Chatham and Pitt Islands, and of the few left these tended to be found in places where sheep, horses, cattle and goats couldn't reach, such as cliff faces and near shore rock stacks, or close to settlements such as Kaingaroa. So if you really wanted to see this plant you had to go to such places as Mangere Island Nature Reserve - which is not that easily accessible to the general public.

Since 1996 the Department of Conservation staff of the Chatham Islands Area office has been working alongside interested landowners on a program of fencing off sow-thistle sites, collecting seed from remnant populations and planting new populations in more secure site on the main islands. This work plan has been incredibly successful and now there are numerous places on the islands and Chatham Island especially, where the sow-thistle is thriving and actively expanding its range. As for the rust, it is now in accidental cultivation at the Area Office garden. It is hoped that in time we can plant rust-inoculated plants into the wild at other sites - so achieving a New Zealand first for fungal conservation by the deliberate conservation management of a critically endangered rust.

In 2009 the New Zealand based Threatened Plant Panel has recognising the successful management of Chatham Islands sow thistle by downgrading its threat status to "At Risk/Recovering". It is pleasing to note that Chatham Island sow-thistle is one of four plants unique to the islands such as Chatham Islands Spear grass (Aciphylla traversii) and Moriori Flax (Astelia chathamica) whose decline has been reversed to such levels that they are now classified as "At Risk/Recovering". Notably these achievements have been achieved through a mix of personal dedication, direct management, advocacy and the willingness of Chatham Islanders to have a part in saving their unique flora.