Lathraea clandestina, the 'Purple toothwort',
is a parasitic plant, living on the roots of trees, preferring Salix
(Willow), Alnus (Alder), and Populus (Poplar). The purple
flowers, which appear in Spring, are the only part visible above ground.
The Lathraea is plentiful around the lake at Cambridge University
Botanic Garden, and can also be found naturalised near the River Cam outside