Overview
Snares Island forest comprises two species of tree daisy: Olearia lyalli and Brachyglottis stewartiae, the former being the dominant species on the islands. Both have a very southern New Zealand distribution between the Snares in the south (with Olearia lyalii also found on the Auckland Islands) and the Solander Islands, Foveaux Straight in the north. Shrubland consists of the white-flowered variation of Veronica elliptica which occurs on the coast and on the hill tops, mostly bordering Olearia forest. The Veronica quickly colonises areas of forest windthrow and dieback. Tussock grassland is dominated by Poa tennantiana (wide-leaved) and Poa astonii.
A major feature of sub-antarctic plant communities is the megaherbs. This feature is limited to only two sites on the main island of the Snares. They contain the impressive Stilbocarpa robusta and Anisotome acutifolia. The latter is the only vascular plant species currently recognised as endemic to the Snares Islands. An entity of Cook's scurvy grass described in 2013, Lepidium limenophylax, is also associated with these herbfields but mainly grows along the western and northern cliff tops of North East Island. Due to the limited area that they occupy, these last two species are listed as threatened. However, the populations on North East Island were stable and healthy in 2013.
There are two low-lying herbaceous plants on the Snares with a New Zealand distribution limited to the sub-antarctic islands: Callitriche antarctica (which thrives in coastal and inland seepage areas) and Stellaria decipiens (glabrous native chickweed). Other low stature species include a cushion plant (Colobanthus muscoides), a succulent herb (Crassula moschata), a small rush (Isolepis cernua) and a sedge (Carex trifida).
The islands have always been free of introduced mammals but two introduced species of plant have made it to the main island. These are Stellaria media (hairy chickweed) and a grass, Poa annua. The Department of Conservation are attempting to eradicate the invasive Stellaria media. Only occassional plants were seen on Gull Point in Boat Harbour, North East Island.