Alternanthera denticulata (amaranthaceae) in New Zealand: A new addition to the indigenous or naturalised flora?

Alternanthem denticulata (Amaranthaceae), an Australian species, is recognised from New Zealand from where it has been collected since the late 1800s. It is known in the North Island from several localities in Northland, Auckland, Coromandel Peninsula, northern Waikato, and the Bay of Plenty. At a number of sites A. denticulata occurs in indigenous wetland habitats, and as its fruit are likely to be dispersed by birds it probably arrived naturally from Australia and is therefore considered to be an addition to the indigenous flora of New Zealand. However, at other sites it has been collected from disturbed and modified habitats and it appears to be naturalised. Previous New Zealand flora treatments have misapplied the name A. denticulata as it has been widely confused with more common A sessilis. A description of A. denticulata is provided based on New Zealand plants, its indigenous status is discussed, and a revised key to New Zealand species of Alternanthera is presented.