A Hampshire site for rare orchids has been mown by mistake, leaving the protected plants at risk.
It is the third year the Narrow-leaved Helleborine at Mascoombe Bottom in the Meon Valley have been cut too early by Hampshire County Council contractors.
The council said cutting the protected orchids, which means new seeds cannot grow, was a "mistake".
Dominic Price, of charity Plantlife, said it was "a massacre of one of the UK's rarest species."
Hampshire's environment councillor Mel Kendal said: "I will be ensuring the council's procedure is changed so that all the designated verges of ecological importance, among the 4,000 miles of rural verges we cut, are individually assessed to protect rare species of plantlife."
The council says it will now mark all rare species with white posts to avoid the mistake happening for a fourth time.
The orchid, which flowers between May and July, is classed as "vulnerable" meaning it is considered to be facing "a high risk of extinction in the wild".
It is found in less than 80 sites in the UK, but has thrived at the verge in Mascoombe Bottom for 50 years due to its south-facing slope.
Narrow-leaved Helleborine is protected under Section 41 of the Natural Environment and Rural Communities (NERC) Act 2006, which requires local authorities to "have regard to the conservation of biodiversity in England, when carrying out their normal functions".