Media playback is unsupported on your device Media caption Leanne Wood: "If I'm not first minister after that election in 2021 I will walk away"

Leanne Wood faces a challenge for Plaid Cymru's leadership unless she agrees to share the job, a Plaid AM has said.

In a highly critical intervention, Adam Price said the party had resorted to "predictable, plodding politics".

Mr Price - urged by his local party activists to mount a challenge - said a male/female co-leadership was needed if Plaid was to win the 2021 election.

Ms Wood has said she will stand down if she does not become first minister at the next assembly election.

Under Plaid rules a window to challenge for the leadership comes around every two years, with assembly members having until Wednesday to step forwards to fight for the role.

Ms Wood has not faced a challenge since being elected leader in 2012, but in a damning article in the Western Mail on Monday, Mr Price slates the party's progress and strategy on independence, saying change is needed "badly" and "fast".

But claims by Carmarthen East and Dinefwr AM Mr Price that Plaid Cymru has lost 1,000 members in eight months were denied by the party.

Another possible contender, Ynys Mon AM Rhun ap Iorwerth, has said he is considering whether to stand.

Mr Price says simply ousting Ms Wood would "leave a toxic residue of bitterness and recrimination" and instead sets out plans which would see Ms Wood stay in power, while sharing the role with a man.

"I have to say it's my view, and I believe that of many others in this great party, that we have generally failed to consistently articulate a comprehensive and compelling vision of the future," he writes.

"Our comfort zone has been a strange mixture of philosophical abstraction and the predictable, plodding politics of the parsimonious press release, the tired tweet and the formulaic Facebook status.

"Nowhere has this shallowness been more exposed than on the question of independence, our very raison d'être, where our failure to present a clear and persuasive exposition explains why we have lost more than a thousand of our eight thousand members in the last eight months.

"Pressing the reset button for our party has to start now; and it comes with the hard but vital work of developing a creative and credible body of ideas that will excite the interest and inspire the confidence of the people of Wales."

Image caption Carmarthen East and Dinefwr AM, Adam Price, and Rhun ap Iorwerth in Ynys Mon, have been called on to challenge Ms Wood, but have yet to put their names in the hat

Mr Price writes that having a man and a woman jointly leading the party would give Plaid a "radical and powerful leadership that will avoid the traditional vulnerabilities of placing power in a single pair of hands".

"In our own party, co-leadership would allow us to embrace all viewpoints, to harness all drive and commitment for the widest political progress possible," he adds.

But Plaid Cymru AM Simon Thomas said co-leadership had been tried before in Plaid and had been "disastrous".

"Either back Leanne to lead or challenge her. There's no easy route to the top," he tweeted.

Alun Lenny, a Plaid councillor in Carmarthenshire who has urged Mr Price to mount a challenge, told BBC Radio Wales he could not see why the party could not harness "the considerable talents we have" by having two leaders.

Speaking on Good Morning Wales, Mr Lenny said he voted for Ms Wood in the 2012 leadership contest, but added: "At best we are flat-lining,"

Analysis by Aled ap Dafydd, BBC Wales political correspondent

Image caption Does Adam Price really want to share the job with Leanne Wood, asks Aled ap Dafydd

The greatest risk is that today's intervention leaves many questions unanswered at a time when Plaid desperately needs stability.

Does Adam Price really want to share the job with Leanne Wood?

What if Ms Wood rejects the offer and Adam Price wins a leadership election only for party members to reject co-leadership?

None of this detail has been thought through.

More from Aled

Also writing in the Western Mail on Monday, Mr ap Iorwerth said: "I'm on the record saying I'm considering my response to Leanne's invitation for a debate on the leadership.

"What that means in reality is that I'm speaking to as many people as possible about how best to take Plaid Cymru forward. We're in this for Wales, not ourselves."

BBC Wales understands Mr Price would be willing to see MPs as well as AMs stand for election as co-leader, subject to a change in party rules.

It is understood that Mr Price wants Ms Wood to commit to his proposal at an assembly group meeting on Tuesday.

Plaid Cymru chief executive Gareth Clubb said the party did not recognise the membership figures quoted by Adam Price.

"Our membership is currently growing and we are confident that it will continue to do so," he said.

The party said it had around 8,000 members in April - Mr Price suggested the figure was 1,000 fewer.

A spokesman for Mr Price said he stood by his figures.

On the call for co-leadership, a spokesperson for Ms Wood said: "All proposals will be considered and will follow the appropriate procedures.

"I am sure all of us are determined to ensure that we continue to work in the most open and democratic manner possible."

Image caption Elfyn Llwyd: "If you're not moving ahead... something is wrong"

There has been mounting appetite within the party for a leadership challenge, with former Plaid leader in Westminster Elfyn Llwyd calling for a change in direction for the party and local constituency parties calling on both Mr Price and Mr ap Iorwerth to stand.

Three other Plaid AMs - Llyr Gruffydd, Sian Gwenllian and Elin Jones - have signed a letter calling for a competition.

On Saturday 53 councillors from across Wales - who make up about a quarter of Plaid's councillors - pledged their support to Ms Wood to continue as leader.

Ms Wood has previously said she would welcome a leadership challenge.

Sam Smethers, chief executive of women's rights charity the Fawcett Society, said: "The under-representation of men in our politics is not the problem.

"But we do support job-sharing of MP and leadership roles. It is good to see that Adam Price does too."