Rare plant discovered in Whangamarino wetland threatened plant survey

The team was especially excited about finding Utricularia australis or yellow bladderwort. Photo / DoC

A threatened plant survey in the Whangamarino wetland rediscovered a seldom-found aquatic carnivorous species.

The last threatened plant survey at the wetland area near Te Kauwhata was conducted in 2009.

Covering almost 7000ha in the Waikato, Whangamarino is the second largest freshwater wetland in the North Island and is one of three RAMSAR wetlands in the Department of Conservation's (DoC) Hauraki-Waikato-Taranaki region.

Waikato District biodiversity ranger Lizzie Sharp says: "We were particularly excited when we found Utricularia australis, the yellow bladderwort, an aquatic carnivorous plant. We had several ID books out and a lively debate about whether it was yellow bladderwort or the invasive weed Utricularia gibba, the humped bladderwort."

The difference between the two plant species is the number of divisions in the leaves, and closer inspection by the team revealed it was yellow bladderwort, which is known only in the North Island.

Senior biodiversity ranger Nigel Binks says the discovery of the yellow bladderwort is exciting, because like all endangered plant species in Whangamarino, it is threatened by competition from encroaching weeds, drainage and decreasing habitat.

The DoC survey team waded around the wetland for 12 days searching for botanical treasures. Photo / DoC

Sharp says: "Yellow bladderwort was found at one site in the 2009 survey, and prior to that, at 11 sites based on historic data. By 2009, 10 of those sites had been infested with humped bladderwort, and as more than 10 years have passed since that survey, we expected the worst – that we would not find any specimens from this unusual and rare species."

On occasion, threatened plant species are also collected by plant enthusiasts or botanists.

Binks says: "This survey will help us make a plan as to what weed control we need to prioritise and which habitat types to protect to better manage plant population declines."

The survey was conducted by Waikato District biodiversity rangers Lizzie Sharp and Kerry Jones and plant expert Britta Deichmann who waded around the wetland for 12 days between September 2020 and April 2021, searching for botanical treasures.

Travel through dense vegetation in boggy water is slow and physically challenging work, taking several hours to cover 1km.

The team also spotted a couple of matuku or Australasian bittern out in the swamp. Whangamarino Wetland is home to the threatened and elusive bird, which can be heard booming during early summer mornings. It is currently classified as "threatened- nationally critically", with fewer than 1000 in New Zealand.

The bog in the Whangamarino Wetland is treacherous and can be unpredictable, so visits by members of the public are discouraged.

Anyone near the wetland is encouraged to keep an eye out for weeds, and to clean any gear and boots before moving to a new site.

For more information about Whangamarino Wetland and its biodiversity click here.