White clover (Trifolium repens) spreads over all the temperate regions of the world, and in New Zealand is exterminating many native species, including even the native flax (Phormium tenax), a large plant with iris-like leaves 5 or 6 feet high.

Mr.W.L.Travers has paid much attention to the effects of introduced plants in New Zealand, and notes the following species as being especially remarkable.

The common knotgrass (Polygonum aviculare) grows most luxuriantly, single plants covering a space 4 or 5 feet in diameter, and sending their roots 3 or 4 feet deep.

A large sub-aquatic dock (Rumex obtusifolius) abounds in every river-bed, even far up among the mountains.

The common sow-thistle (Sonchus oleraceus) grows all over the country up to an elevation of 6000 feet.