The best impression of how the Heath must have looked in past centuries can be gained by looking at Vanbrugh Pits, particularly the deeper, northern pit. Photographs from the 1890s (Rhind 1987) show that the vegetation of Vanbrugh Pits has changed little over the last hundred years.
Gorse and broom, typical heathland shrubs which once covered much of Blackheath, are still abundant here, along with occasional young trees of oak and silver birch.
Some of the latter have been planted, but others are self-sown. Beneath the scrub and trees, wood sage can be found. This characteristic plant of woods and scrub on acid soils is distinctly uncommon so far into London.
Much of the flat floor of the pit is covered in acid grassland, characterised by an abundance of sheep's sorrel, a small member of the dock family with arrow-shaped leaves which turn red in summer.
Common bent is the dominant grass, with red fescue also frequent. The tiny early hair-grass, rather scarce in London, occurs on barer patches, where mountain bikes have caused erosion.
Other wild flowers of the acid grassland include cat's-ear and autumn hawkbit, two rather similar plants with yellow, dandelion-like flowers; they can be told apart by the bristly leaves and larger flowers of cat's-ear.
A small population of harebells also survives in the acid grassland of Vanbrugh Pits, the only place on Blackheath where these beautiful flowers can be found. Also to be seen among the grasses, on a very close inspection, are Cladonia lichens, their fruiting bodies resembling tiny cups.
Elsewhere on the floor of Vanbrugh Pits, and also on the banks, the natural acid grassland vegetation grades into a coarser grassland of cock's-foot, false oat-grass and Yorkshire-fog, indicating some past enrichment of the soil.
Common but colourful wild flowers growing on the banks include common mallow, creeping buttercup and thistles. Also on the banks, surely as a result of deliberate sowing, are a few plants of field scabious and greater knapweed, both very rare in this part of London and typical of chalky soils; it is unlikely if either will survive for long. Alexanders, a plant usually associated with coastal habitats, was found on the edge of the pits in 1999.