Biological flora of the British isles:: Mercurialis perennis L.

1. This account reviews information on all aspects of the biology of Mercurialis perennis that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation. 2. Mercurialis perennis is a dioecious, clonal, perennial forb of woodland, hedgerows, limestone pavement, screes and tall-herb communities. It is very tolerant of low light; it can also grow in unshaded conditions, although higher light flux densities result in lower shoot biomass. It is Eurocaucasic, occurring throughout temperate areas of Europe as far east as the Russian border. 3. Mercurialis perennis occurs on a wide variety of soil types over a pH range from 4.3 to 8.5, although it is most abundant on more base-rich clay or loam soils with a low organic content. It seldom occurs on peat or very sandy soils. It can grow in soils with low availability of macronutrients but it responds positively to nutrient addition from atmospheric or agricultural sources. It is intolerant of waterlogging, mainly because of poor aerenchyma development; its limited capacity to oxygenate the root environment can lead to ferrous ion toxicity. The resulting superficial root development on heavy soils may confer drought susceptibility in summer. 4. Mercurialis perennis is predominantly wind-pollinated. Ants are the main dispersal agents and the seed bears an elaiosome which offers them a lipid-rich reward. Establishment from seed is uncommon and vegetative propagation is the main means of expansion, often leading to dense clonal stands of aerial shoots. 5. Mercurialis perennis has been described as a stress-tolerant competitor. The persistence of its clones and slow dispersal have led to it being regarded an as indicator of ancient, semi-natural woodland.