In a dramatic turnaround after years of cooperation between the two groups, Turnpike Authority chairman John Cogliano said at a board meeting he was sending a letter to the horticultural society informing the organization that “the authority can no longer support its proposals for the Greenway parcels.”

The 178-year-old Massachusetts Horticultural Society will fight the authority ; the society’s board recently voted unanimously to continue to plan and develop the parcels as parks.

The society was unable to deliver its original vision of a “winter garden” on the Greenway, and experienced financial hardship and turnover at the top. Under new leadership, the horticultural society more recently proposed creating extensive gardens, a first phase of which would be complete in 2008, and is to receive Turnpike Authority help amounting to at least $2 million.

The authority ’s new position on the society came two months after the chairman of the conservancy that oversees the Greenway, Peter Meade, argued that the group should no longer be allowed control of those three blocks.

Yesterday Meade said he was pleased the Turnpike Authority now wants to start fresh. “We have to examine the options, and you can’t go through a thorough examination of those options with the community while you still have someone working on the parcels,” Meade said.