National Party leader Simon Bridges says Marama Davidson's election as Greens co-leader makes it less likely the two parties can work together in the future.

Ms Davidson became the new Greens leader alongside James Shaw on Sunday morning after beating out contender Julie Anne Genter.

Mr Bridges had earlier changed his party's direction by saying he was willing to work with the Greens on "genuine conservation issues", in what was seen as a signal he was open to a possible alliance in government one day.

However, on Monday he said he viewed Ms Davidson's election as a "move to the left" and a sign there would be less common ground for the parties to agree on.

"I want to work with the Green Party on genuine environment and conservation issues but not on a picketing and anti-business agenda," he told TVNZ.

"They've made the choice for themselves, which definitely represents a leftist agenda rather than a very strong environment one."

Ms Davidson responded by saying the Greens' role was to act independently and not cosy up too closely with any major political party.

"Our role as an independent party is to push the government to be bolder and more progressive," she said.

Ms Davidson's election comes after Metiria Turei stood down as co-leader last August following scrutiny of her public admission to committing benefit fraud in the early 1990s.

The 2017 election results that followed were the worst for the party in more than a decade, but the Greens still ended up with ministers in the Labour-led coalition government.

Ms Davidson is reported to have campaigned for the co-leadership on her ability to criticise Labour more openly because she is not a minister.

She is the third female co-leader in the party's 23-year history, after Jeanette Fitzsimons and Ms Turei.