The gall of it!

Galls, which can range from the delicately beautiful to hideously unattractive bulbous growths, are among Nature's most intriguing phenomena, discovers Deborah Nicholls-Lee

- Deborah Nicholls-Lee

SOME are pinned to leaves like delicate jewel brooches, whereas others are disfiguring bulbous growths that squat on plants like alien invaders. Galls-abnormal growths on plants and trees caused by parasitic organisms-are among the most intriguing of Nature's creations and can be both beautiful and horrifying. The charming cherry gall, for example, adorns oak leaves with delicately speckled red baubles and the unseemly horned oak gall wraps itself around branches like the clawed toes of a hideous monster. All capture the imagination and all are formed from the plant's own tissue, altered by physical injury or alchemised by chemical secretions.

The most common culprits are invertebrates: often tiny gall wasps, less than half an inch in length, or flies, mites and aphids. As aphids nibble plants, chemicals in their saliva induce the formation of galls, creating popup furniture among which they can feed and reproduce. For other invertebrates, such as wasps, laying their eggs on a plant stimulates the growth of a gall, which cocoons the larvae in a protective and edible nursery, rather like a chick within an egg.

Due to the range of insects engaging with it, and the many different places on a plant that a gall can form (leaves, catkins, buds, acorns or roots, each with a differing result), a single species of plant can yield an abundant variety of galls. In the UK, about 70 different gall wasps interact with oak, for example, creating an entire curiosity cabinet of galls with evocative names, such as the artichoke, the marble and the silk button.