Chemical sprays on farmland around Stonehenge, the prehistoric ruin on Salisbury Plain in southern England, may have killed off rare lichens that had grown on the stones for 5,000 years.
Inspectors who climbed the monument last week found that 18 species had disappeared in 20 years.Dr. Francis Rose and Peter James were asked to study the stones as part of a survey.
Rose and James recorded 66 species, including one, Physcia sciastra, never before found in southern England.
But hopes of finding the lintels and other exposed stones rich in species were dashed.
"We believe the lichens have suffered from chemical sprays drifting from nearby fields," Rose said.
Fallen stones sheltered from the spray bore a greater variety of species. The so-called "Slaughter Stone," at which Druids are said to have made sacrifices, had 20 species growing on it.