Country diary: Bonsai birches grow in the tree's crown

The Marches, Shropshire: Witches' broom is a curious thing - the result of a fungus and looking like a bird's nestThe thin swift of a new moon rises through cirrus. Sunlight on the last leaf flashes oak-gold, bracken-rust. Many birches are fiery yellow, but some of the older trees are already stark against the sky. In the black-veined architecture of silver birches, Betula pendula, there are curious structures. They look like pubic tufts or birds' nests, or what happens if birds and their nests become one thing.There is witchcraft in this, like the combs of care that cause knots in hair, that speaks of familiar lingering shadows of story. These clusters of twigs are witches' brooms - however, this spell was not cast by human agency but by a yeast-like fungus, Taphrina betulina. Perhaps carried by an aphid, mite or other leaf-biter, the fungus enters a birch leaf bud in spring. It carries growth regulators, which penetrate the bud's cells, disrupt them and cause a gall - a tumour. The bud goes haywire and, instead of a single leaf, multiple shoots sprout with their own buds but in miniature, like tiny bonsai birches. I'm sure I've heard of witches' broom shoots being propagated to create dwarf or weeping birch clones. Continue reading...