T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Hieracium pilosella (Mouse-ear Hawkweed)

Kingdom: Plantae
(Unranked): Angiosperms
(Unranked): Eudicots
(Unranked): Asterids
Order: Asterales
Family: Asteraceae
Genus:      Hieracium
Species: H. pilosella
Binomial name: Hieracium pilosella
Syn.  Pilosella officinarum
Common name: Mouse-ear Hawkweed

Mouse-ear Hawkweed is a perennial, stoloniferous flatweed with extensive underground root mass. It is a yellow-flowered species of Asteraceae, native to Europe and northern Asia. It produces single, citrus-coloured inflorescences. It is an allelopathic plant. Allelopathy is a process by which a plant releases chemicals that can either inhibit or benefit other plants. Most allelopathic plants cause harm to other plants.
Like most hawkweed species, it shows tremendous variation and is a complex of several dozens of subspecies and hundreds of varieties and forms. Several of the European hawkweeds Hieracium spp. has been introduced to New Zealand and North America. The mouse ear hawkweed Hieracium pilosella invades pastures, roadsides and natural areas. It is a rapid colonizer and forms dense mono-specific patches of small, flat rosettes that can cover up to several hectares in an area due to its vegetative (stolons) and sexual reproduction; seeds also form asexually by apomixis. Mouse-ear hawkweed has the ability to alter soil nutrient status, replace native flora and decrease palatable forage in pastures. Sheep and livestock avoid the mouse-ear hawkweed because of its prostrate growth habit and highly pubescent leaves.
In New Zealand, Hieracium pilosella is considered a sleeper weed, as it was first introduced to the country in 1878 but remained localised for around 80 years. After this lag phase of at least 80 years, the population suddenly increased its range dramatically. It has now spread significantly into tussock grasslands used for grazing and into conservation areas. H. pilosella excludes native species by out-competing them.

Notice the hairy leaves

Photo showing the dense patches it forms

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/