THE Scottish Greens are often thought of as lightweight. They have been accused of being the “gardening wing” of the SNP – and Press Association pictures filed on Friday of their leaders sitting amongst flowers would seem to justify that.

It was no doubt this reputation which in part led Humza Yousaf to think he could boot them out of Government without consequence. In August, Yousaf about admitted as much – saying he thought the Greens would calculate that to react negatively against his decision would be “political suicide”.

But Yousaf was swiftly proven wrong. The Greens reacted with anger – among other emotions, as MSP Gillian Mackay memorably cried on the radio about the end of the deal with the SNP.

The then-SNP leader saw a different side to the party: a ruthless one. The Greens were happy to force his resignation, which came just days after they were removed from government. Yousaf summed up the situation succinctly: “I, frankly, f***** up.”

Scottish Green MSP speak to the media after the end of the Bute House Agreement (Image: free) On Saturday, the first day of the Scottish Green conference in Greenock, it was the Greens who brought Yousaf down that turned up.

Ahead of key negotiations on the Scottish Budget, the messaging was clear: this is a party coming out fighting.

It was in that vein that Patrick Harvie issued a stern warning to the SNP in his keynote speech: “As Scottish Green MSPs, we have a responsibility to engage with the process in good faith, and with honesty. But as the only party that ever brought down an SNP budget, as John Swinney knows to his cost, we need to be clear that they cannot take our votes for granted.”

Swinney will no doubt remember – and be keen to avoid – a repeat of the 2009/10 Budget debacle to which Harvie was referring.

READ MORE: SNP 'must show they can be trusted' for Greens to back Budget, Patrick Harvie says

In a last-minute decision, the Green MSP pulled support for the SNP Budget after then finance secretary Swinney refused to include £11 million for a house insulation programme.

The Green move couldn’t have been much more last minute – STV political editor Colin Mackay recalled seeing “tears amid the anger among SNP ministers” in the debating chamber as they realised what was about to happen.

In the fall-out, then-first minister Alex Salmond said he had put his SNP on an election footing and was ready to go to the polls early.

In her own warning to the Scottish Government, Green co-leader Lorna Slater said she was “absolutely” prepared to force the SNP into an early election.

Lorna Slater photographed in Greenock ahead of the Green conference (Image: Jane Barlow/PA Wire) "The Scottish Greens are polling really well at the moment. The SNP are in a difficult position,” she told The Herald.

But the Green conference also highlighted something else about the party. More than any other in Scottish politics, the Green constitution puts its leaders and MSP group under the control of members.

Giving members such power does make the party more democratic – and prevents it from doing as Labour and the SNP do and simply ignore policies agreed at conference. But it also makes it more unpredictable – and much harder to control.

READ MORE: Greens 'will not back SNP Budget with less than £4.7bn for climate', conference told

It was that unpredictability which also played a hand in the Greens being removed from Government, as their own members were looking to force a vote on whether they should be the ones to end the Bute House Agreement. Yousaf couldn’t risk the embarrassment.

Again that unpredictability reared its head at the conference on Saturday, when an unexpected point of order led to members voting down the entire agenda. Party officials were sent to redraw it, leaving things in limbo and key votes pushed back – while others may not take place at all.

It was not ideal timing considering Harvie had just spoken that morning about the Greens "becoming the effective and professional political force we are capable of being".

The message from conference is then that the Scottish Green leadership is ready to get serious – but can they inspire the membership to go with them?