Pilosella officinarum F. Schultz & Schultz-Bip. (Hieracium pilosella L.)
Perennial Broad-leaved Weeds
Mouse-ear-hawkweed is a stoloniferous perennial, native in short grassland on well-drained soils. It occurs on calcareous pastures, heaths, banks, rocky places and walls, and is locally common throughout the British Isles. It is a weed of degraded pastures, poor lawns and other sparse vegetation. It thrives in areas of low rainfall and is able to recover from apparent desiccation, although, seedlings and young rosettes may be killed. Mouse-ear-hawkweed can tolerate a broad pH range but it cannot withstand a high water table and is absent from wetland. It does not occur in woodland or other shady places.
Mouse-ear-hawkweed is a very variable species. Numerous subspecies have been described in the past but only 7 are said to occur in Britain. Hybrids with related species also occur.
It forms pure stands that exclude other plants and it has been suggested that mouse-ear-hawkweed has an allelopathic effect. It contains a number of phenolic compounds with phytotoxic properties. Leachate from the roots inhibits the germination of its own seeds. Extract of mouse-ear-hawkweed has anti-bacterial properties and has been used as an antibiotic against brucellosis. It has also been used as a herbal treatment for respiratory infections.
Mouse-ear-hawkweed flowers from May to October. Peak flowering may occur in June with a second flowering in late summer. The flower stalk continues to elongate from bud formation through to fruiting. Seed is produced both apomictically and by insect pollination. Apomictic seeds are essentially clones of the parent. Open pollinated plants are visited by many different insects and are self-incompatible. Seed is set within a few weeks of flowering. Seed numbers in individual flower heads range from 63 to 130.
Seeds show great variation in viability. Freshly shed seeds germinate readily but there is some evidence of dormancy. Germination levels may increase following a period of dry storage. Storage at 5°C increased the germination level from 47 to 81% over a 12 month period. Storage at room temperature had no effect. Light may be required for germination under some circumstances. Seeds sown in the field and cultivated periodically emerged mainly in June-July and in September. Emergence tended to follow soil cultivation. Seeds may germinate in gaps in grassland but seedlings rarely succeed in established vegetation.
Mouse-ear hawkweed usually develops flat rosettes in grazed grassland. The rosettes are formed on a slender rootstock. New daughter rosettes are produced seasonally on stolons, or in the leaf axils of senescing rosettes, or from the underground bud bank on the rootstock. Stolons grow up to 30 cm long, are sometimes branched and usually have a rooting, terminal rosette of overwintering leaves. The number, length and degree of branching of the stolons depends on the population density. Stolons form on rosettes that are due to flower. Rosettes may take from 1 to 4 or more years to flower. Within a few months of flowering the parent rosette senesces and the stolons decay leaving independent daughter rosettes. The rosettes may suffer frost damage over the winter but mortality is negligible.
Persistence and Spread
Seed sown in the field remained viable over a 5-year period but seedling emergence had declined by year 5. Seedlings can remain in a juvenile, non-rosette form for several years. Individual plants may live for over 10 years but ageing clones may lose vigour and some seedling development is essential for the population.
Mouse-ear hawkweed can be a serious weed in nutrient poor, overgrazed pasture. Plants should be spudded out to prevent seeding. Improvements such as increased fertility and the prevention of rabbit grazing can lead to a dramatic decline in mouse-ear-hawkweed. The weed benefits from rabbit activity except in drought conditions when the rabbits may eat into the stolons. Rabbits rarely eat the rosettes but feed on the developing flower stalk and buds. Under heavy rabbit grazing all the flowers may be removed. Sheep also eat the flowers.
Mouse-ear-hawkweed is attacked by various insects that feed on the leaves and sap. The caterpillars of several butterfly species are found on it. A limited number of pathogens infect it including a rust fungus.
Updated October 2007.