Plagianthus is a genus of flowering plants confined to New Zealand and the Chatham Islands.

The familial placement of the genus was controversial for many years, but modern genetic studies show it definitely belongs in the Malvaceae subfamily Malvoideae.

[1] The type species P. divaricatus is a divaricate shrub which grows at the edges of salt marshes.

The other species, P. regius is a tree which in juvenile stage may be divaricate (subsp.

In the past, species from related genera such as Hoheria (New Zealand), Asterotrichion, Lawrencia and Gynatrix (Australia) were sometimes assigned to the genus.