Lord Elis-Thomas was speaking ahead of Plaid's 80th anniversary

Lord Elis-Thomas said he was not celebrating the party's 80th birthday on Friday because of the need to look forward to a brighter political future.

The Welsh assembly's presiding officer said Plaid was the least successful party to respond to devolution.

But Plaid said it had an "impressive record" since the Welsh assembly was set up in 1999.

Lord Elis-Thomas, Plaid president between 1984 and 1991 and AM for Meirionnydd Nant Conwy, said the only point of voting for any opposition party was if that party was serious about playing a part in government.

Plaid has rejected entering a coalition with the Conservatives and Liberal Democrats to topple the minority Labour administration at the assembly.

Lord Elis-Thomas said: "There seems to be a feeling that we are aligning ourselves almost as a perpetual opposition.

"Well, that doesn't make a party electable."

'Impressive record' - Plaid

In a statement, Plaid Cymru said it had put its policies at the top of the political agenda since the establishment of the assembly.

Plaid said: "When the assembly was established, (former Labour Welsh Secretary) Ron Davies said it was a settlement for a generation.

"Within five years, Plaid have exposed the failings of Labour's talking shop assembly and placed a parliament for Wales at the forefront of the political agenda.