Hypochaeris radicata
(cat's ear)

H. radicata is a herbaceous perennial originally native to Morocco. It is a very successful colonizing species that is now present on all continents except Antarctica (Ortiz et al., 2008). In New Zealand, Healy (1992) described the distribution of the introduced H. radicata as ‘one of, if not the most widely distributed introduced weeds on a geographical and altitudinal basis.’ It is considered one of the most invasive alien plants on the island of La Reunion (ISSG, 2013). H. radicata readily invades freshly disturbed environments, such as Mount St. Helens following its 1980 eruption (Schoenfelder et al., 2010), and can crowd out more palatable and productive forage species when it invades overgrazed pasture and rangeland (DiTomaso et al., 2013). PIER (2014) indicated it is invasive in a wide range of territories and islands around the Pacific.

H. radicata is a very successful colonizing species that is now present on all continents except Antarctica (Ortiz et al., 2008). It tends to be distributed in cooler, temperate parts of the world (Turkington and Aarssen, 1983). Its northern limit may be controlled more by winter cold than by lack of summer warmth.

Both Turkington and Aarssen (1983) and Ortiz et al. (2008) have questioned whether the species is truly native to the UK and Europe. Ortiz et al. (2008) proposed that the native area of distribution should be North Africa, the Iberian Peninsula and the central (and possibly eastern) Mediterranean.

Although widespread in the USA, H. radicata seems to have stabilized there and, according to DiTomaso et al. (2013), is not likely to expand beyond its present habitats. 

In its ancestral range in Morocco, H. radicata preferred humid Mediterranean woodlands (Ortiz et al., 2008). It has since expanded its range to include a wider variety of habitats; in particular, grasslands and waste places of various kinds have also become the natural home of H. radicata. It can be found along roadsides, in orchards, vineyards, landscaped areas and gardens, often as a lawn weed.

In the UK, H. radicata is primarily a plant of regularly cut or grazed neutral grasslands, of grassland on sandy soils, and of man-made habitats with bare soil. It is most often found in pastures and lawns, on roadside verges and banks, on fixed dunes, in cliff-top grasslands, in waste places in built-up areas and on raw soil (Turkington and Aarssen, 1983).

In New Zealand it is ‘abundant in waste places, pasture and modified tussock grassland through both islands and extending from sea-level to the upper level of vegetation on the mountains’ (Healy, 1992).

In Australia, Weeds of Australia (2013) described it as ‘possibly the most widely distributed weed in south-eastern Australia’, and ‘a very common weed of parks, gardens, footpaths, lawns, roadsides, disturbed sites, waste areas, cultivation and pastures,’ but commented that it is also common in natural habitats.

In British Columbia, H. radicata has been recorded from swamps, ditches, forest edges and clearings, on beaches and cliffs and in grazed pastures and grass/forb and sedge communities (Aarssen, 1981). It is rare in the Canadian prairies.

In California, CAL-IPC (2013) described H. radicta as invading sites relatively undisturbed by human activity, but more invasive and prevalent on disturbed sites such as grazed or burned lands, especially those in coastal areas. It is widespread and abundant in coastal terrace prairie and coastal bluff scrub, often one of the more dominant species.

In Japan, it is found in all temperate areas, often in grasslands (Doi et al., 2006).

H. radicata tolerates a wide range of soil texture and pH, having been found from light sand and gravel through to clay, and from soils with a pH of 3.9 to those with pH 8.6 (Turkington and Aarssen, 1983). It occurs on some of the driest soils in the UK, but in continental Europe it prefers moist, well-drained sites, although it is absent from sites subject to prolonged waterlogging. 

Genetics

Recorded diploid counts for both British and Canadian plants are 2n=8 (Aarssen, 1981; Turkington and Aarssen, 1983). Panigrahi and Kammathy (1961, cited in Aarssen, 1991) reported occasional trisomics with 2n = 9 for Indian plants.

Reproductive biology

Ho (1964, cited in Aarssen, 1981) found that mature, flowering plants can be produced from seed in as little as 2 months under favourable conditions in British Columbia. According to several sources (Fryxel, 1957; Parker 1975), H. radicata is cross-pollinated and self-incompatible. Picó et al. (2004) observed that selfing dramatically reduced seed set, but the few selfed seeds produced were larger and had a greater chance of surviving to flowering than outcrossed seeds. This ability to self-fertilise may be important for isolated individuals that are the first to reach new habitats.

Flowering begins in response to long days, in May in British Columbia and in June in the UK, and continues until October or September (Salisbury, 1964; Aarssen, 1981). Although Salisbury (1964) claimed that ‘the flower heads close at night but open in daylight even when it is dull and cloudy’, Percival (1950) said that sunlight is necessary to stimulate the flowers to open in the morning, and that the flowers do not open in rain or if rain and sun alternate for about half an hour each. Once the flower is open it cannot close for at least 3 hours. In warm sunny conditions, flowers may stay open for about 3-4 hours, or up to 6-7 hours in cool cloudy conditions (Percival, 1950). Many insects visit the flowers, some to eat, and possibly disperse pollen whilst others feed on the nectar (and presumably disperse pollen at the same time) (Aarssen, 1981). The honey bee (Apis mellifera) is one of the major beneficiaries of the large amounts of pollen the flowers produce (Percival, 1950).

The fruit heads may total 60 or more on one plant but on average only about 20 are produced, and each one contains about 44 fruits (seeds) but sometimes as many as 136 (Salisbury, 1942). The ripe fruit is orange-brown in colour, 4-5 mm long with about 15 longitudinal ridges and a beak-like apex with a pappus of an outer ring of short simple hairs and an inner ring of feathery ones. The average weight is from 0.6-0.8 mg and germination ranges from 30 to 90% (Salisbury, 1964). Ho (1964, cited in Aarssen, 1981) estimated an annual production of 2329 achenes per plant over a 27 day period in British Columbia.

Soons et al. (2004) simulated wind dispersal of grassland plant seed (one species being H. radicata) and found that ‘autocorrelated turbulent fluctuations in vertical wind velocity are the key mechanism for long-distant dispersal.’ Dispersal distances are greatest under high wind velocity, when mechanically produced turbulent air movements are large. Under very low wind velocity conditions seeds are dispersed further when there is more surface heating, but never as far as when winds are strong.

Physiology and phenology

In the UK the species begins flowering in June and continues until September, usually with a flush in each of those two seasons (Salisbury, 1964). The flower heads in the first flush are often larger, nearly 4 cm across, whilst those of the autumn flush are often about 2.5 cm across. All the individual flowers in the flower head are strap-shaped and yellow but at the margins they have a greenish underside with a purplish tinge. Intermingled with the flowers are many tapering scales.

Ho (1964, cited in Aarssen, 1981) said that freshly harvested seeds did not need a period of dormancy before germination, that light is needed for germination and that seeds lost viability rapidly in dry storage. Immediately after harvest seeds gave 68% germination but after two months of dry storage, this percentage had fallen to 4%. Grime et al. (1981) also found that dry storage (in their case for 12 months at 5^oC) reduced germination from 94% for fresh seed to 31%.

Hartemink et al. (2004) found that regular and continuous removal of flower buds of H. radicata from the onset of flowering until early October led to a 3-4 fold increase in the number of flower buds produced, an increase in the number of flowering stems and greater branching of the flower stems. In addition, when flowering was prevented, plants switched their resources to greater vegetative reproduction and they generated more new rosettes. Struik (1967) found that 20% of his sampled plants (in lawns and grazed pasture) were in clusters of two to six individuals, presumably originating by vegetative reproduction of a single plant.

The rosette leaves can grow very close to the ground, which protects them and buds from mowing or grazing. The perennial roots grow far below the root depth of neighbouring species in lawns, which may explain its high mineral and trace element content (Fagan and Watkins, 1932; Coop et al., 1953; Struik, 1967) as well as its tolerance of drought (Turkington and Aarenssen, 1983). The small epidermal cells of the leaves and the large multicellular hairs (Ormrod and Renney, 1968) may also assist in its drought tolerance. In lawns and possibly elsewhere the plant is often multi-crowned, and the crown may extend 2-3 cm below the ground surface (Healy, 1962).

Longevity

H. radicata is a relatively short-lived species which lives for up to two seasons (de Kroon et al., 1987; Fone, 1989). Plants can overwinter as green leafy rosettes or, in colder climates, above-ground parts die back, leaving perennating buds at ground level (Aarssen, 1981). The seeds do not seem to persist for long in the soil seed bank.

Population size and structure

Ridley (1930, cited in Aarssen, 1981) claimed that H. radicata has been known to displace every other plant in pastures, including white clover (Trifolium repens). Ho (1964, cited in Aarssen, 1981) found little reduction in top and root development or number of seeds produced when plants were growing in grass compared with plants growing alone.

H. radicata may exert allelopathic effects on other grassland species (Aarseen, 1981). Root leachates were found to reduce shoot dry weight of several grassland species (Newman and Rovira. 1975). Leaf extracts caused a significant decline in germination rate and seedling shoot length in Agrostis tenuis (now known as A. capillaris). The same authors found that H. radicata is autotoxic, its own exudates inhibiting its growth by more than that of neighbouring plants, which may explain why it is often found as isolated individuals or in small clusters rather than forming large patches or pure stands (Aarssen, 1981).

Guthrie-Smith (1953) observed H. radicata to be one of the early colonisers after fire in grassland in New Zealand.

Nutrition

Coop et al. (1953) analysed the chemical components of H. radicata in New Zealand: protein 10-15%, fibre 10-20%, calcium 1-2%, phosphorus 0.15-0.5% and copper 5-10 ppm, on a dry matter basis. Grace and Scott (1974) and Turkington and Aarssen (1983) presented further information on the concentration of mineral elements in New Zealand and British plant material.

Brun et al. (2003) experimented with different levels of copper added to soil and measured its effects on H. radicata and other species found in European vineyards, where high concentrations of copper are found in the soil surface due to the repeated use of copper-based fungicides for protection against vine downy mildew (Plasmopara viticola). High concentrations of copper in the soil led to lower survival, lower total plant biomass, a delay in flowering and fruiting, and low seed set in the five species tested. H. radicata was especially sensitive to high concentrations of copper in the soil, although it still produced seeds at all levels of copper except the highest tested (400 mg kg^-1 of added copper, making the total copper load in the soil 558 mg kg^-1).

Associations

Turkington and Aarssen (1983) presented a large table of species associated with H. radicata in the Sheffield area in England, UK, and also listed many communities in which it occurs. In the Sheffield area it was associated with 197 other species, almost all species of open grassland like Agrostis capillaris, Anthoxanthum odoratum, Festuca rubra, Holcus lanatus, Lolium perenne and Trifolium spp.

The stalks of H. radicata often show gall swellings caused by the hymenopteran insect Aulax hypochaeridis. Guthrie-Smith (1953) observed broomrape (Orobanche minor) attached to the roots of H. radicata in New Zealand. Both Aarssen (1981) and Turkington and Aarssen (1983) listed invertebrate species that parasitise or feed on H. radicata, and Turkington and Aarssen (1983) also listed fungi and viruses found on H. radicata (see Natural Enemies table).

H. radicata can be confused with other rosette weeds with similar bright yellow flowers in the same family, including H. glabra, Crepis capillaris, Leontodon autumnalis and the true dandelion Taraxacum officinale (Aarssen, 1981).Aarssen (1981) provided a key for separating these species (but did not include Crepis capillaris), and Healy (1992) provided a useful guide to distinguishing these species. In essence, in the rosette stage H. radicata has rounded leaf lobes, hairs on the leaf margins, a thick, rough leaf surface, and simple leaf hairs. When flowering, it has leafless branched flower stalks and large flower heads. The stalks of both H. radicata and H. glabra often show gall swellings caused by the hymenopteran insect Aulax hypochaeridis.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Physical/mechanical control

Ploughing and cultivating for one or two years before reseeding gave effective control (Aarssen, 1981, quoting the Canadian Dept. of Agriculture). Pigs may exert some control by uprooting plants, but by disturbing the ground they probably aid rapid reinfestation by H. radicata.

The taproot must be cut several inches below the crown and removed to stop it resprouting (DiTomaso et al., 2013).

Chemical control

In Canada, Turkington and Aarssen (1983) mentioned that H. radicata was ‘resistant’ to atrazine and dalapon and moderately ‘resistant’ to paraquat, asulam, picloram and other herbicides. However, they suggested that adequate selective control can be achieved in grassland or turfgrasses with MCPA, 2,4-D, or mecoprop.

DiTomaso et al. (2013) presented a long list of herbicides that can be used to control H. radicata in different circumstances. Some of these are selective and will not affect grasses; others will kill any green plant they contact. The list includes 2,4-D, aminocyclopyrachlor, aminopyralid, chlorsulfuron, clopyralid, dicamba, fluroxypyr, glyphosate, hexazinone, imazapyr, metsulfuron, picloram, sulfometuron and triclopyr.

Control by utilization

The species is considered highly palatable and nutritious to sheep and cattle, although the rosette leaves can be strongly appressed to the ground and may sometimes be hard for livestock to access.

Livestock grazing benefits the growth and reproduction of H. radicata. Struik (1967) studied the size and growth of H. radicata in mown and unmown lawns and in heavily and lightly grazed pastures in New Zealand. Dry weight per plant was least in the mown lawns and greatest in grazed pasture; the greatest vegetative weight was achieved under heavy grazing and the highest reproductive weight under lax grazing. Relative weight of leaves and roots decreased and relative weight of floral organs increased with decreasing stand defoliation. Relative root biomass decreased with increasing relative weight of floral organs. 

: Original text by:

Ian Popay, consultant, New Zealand, with the support of Landcare Research.