Hypochaeris radicata L., Cat's-ear

Account Summary

Growth form and preferred habitats

A frost-hardy, often wintergreen, perennial (at least in mild settings) with all the foliage leaves forming a flattened rosette on the ground and with its overwintering buds held at ground level (ie a hemicryptophyte), H. radicata has a thickened, erect, branched rootstock and fleshy roots that deeply penetrate the soil (Salisbury 1964). All these features taken together provide the species with adequate overwintering resources, excellent drought resistance and a moderately effective means of vegetative reproduction.

H. radicata can be readily distinguished from the species that is most like it, Leontodon autumnalis (Autumn Hawkbit), by its leaves being more densely covered with short, stiff hairs, and from all Leontodon species by scales being present on the receptacle between the florets, which are yellowish and corolla-like in flower, pale brown or silvery-white when in fruit (Webb et al. 1996). Presumably it was the leaf hairiness that gave rise to the English common name 'Cat's-ear' although, in the view of the current author (RSF), the leaf shape and its size certainly do not resemble a cat's ear even in the slightest.

H. radicata is one of the most common, widespread and familiar plants in the flora of B & I. It occurs in a very wide range of habitats, usually involving short turf or bare soil patches in disturbed ground on well-drained, neutral or slightly acidic soils. Typical habitats include more or less dry pastures, meadows, coastal cliffs, screes, mountain heaths, roadsides, hedge banks, waste ground, open scrub and quarries. Cat's-ear is really absent only from deep shade, very wet, very acid, or extremely disturbed or regularly cultivated soils.

The gardener is very often over-familiar with Cat's-ear as an invasive weed in lawns, where the tough, springy flower stems bend with and evade the mower blades, and the flat-lying, basal leaf rosette is just too low to be cut. The plant may also appear as a casual in the vegetable garden.

H. radicata is intolerant of shade and does not usually survive long in competition with taller vegetation, although the normally flattened rosette leaves can grow up to a height of around 20 cm when obliged to by surrounding taller species. In regularly grazed or mown grassland, however, the species is highly competitive and it has been claimed that within three years it displaced every other herb in peaty pastures in New Zealand, including Trifolium repens (White Clover) (Ridley 1930). The established strategy of H. radicata is categorized as C-S-R, meaning it has a mix of properties of all three recognised ecological strategies, Competitor, Stress-tolerator and Ruderal (Grime et al. 1988, 2007).

Although the milky latex found throughout the plant is described as being very bitter, and might therefore render the plant unsuitable as fodder (Salisbury 1964), the species appears perfectly palatable to stock animals. It also tolerates being trampled, but it chiefly survives grazing pressure because many herbivores have difficulty obtaining purchase on rosette leaves that are so tightly appressed to the soil surface (Grime et al. 1988, 2007). However, sheep are known to selectively graze H. radicata, and the plant often invades thin, overgrazed, under-fertilised pastures where it grows surprisingly vigorously and can reproduce very effectively and, in so doing, it offsets the decline in the carrying capacity of the field (Turkington & Aarssen 1983).

Variation

Two subspecies are recognised in B & I although a range of intermediates occur when the two subspecies grow adjacent to one another, so they are not that well separated. Subsp. radicata is the more widespread, taller, more erect of the two, and it has much larger leaves, 8-25 × 1-6 cm. Subsp. ericetorum Van Soest has stems 7-30 cm tall, that are either prostrate, decumbent or ascending. Its leaves are also smaller, 1-12 × 0.5-3.0 cm and it grows at the coast, on shingle, dunes and sandy heaths. Subsp. radicata is the more ecologically varied plant, occupying a much wider range of habitats and localities, particularly non-sandy ground (Sell & Murrell 2006).

Fermanagh occurrence

H. radicata is common and widespread in Fermanagh, having been recorded in 426 tetrads, 80.7% of the VC total. Cat's-ear is absent only from deep shade, very wet, very acid, or extremely disturbed or regularly cultivated soils. Under Fermanagh weather conditions, Cat's-ear over-winters as an above-ground leaf rosette, vegetative growth recommences in March and flowers appear from early June on.

Vegetative reproduction

When the plant is subjected to stress from heavy grazing pressure or regular mowing, the hypocotyl or the crown of the rootstock (ie the thickened, overwintering root and its junction with the stem-base) responds by branching and producing further fibrous roots plus enlarged, tap-root-like roots that together enable the species to spread vegetatively, forming a number of daughter leaf rosettes around and immediately adjacent to the parent plant. In rough grassland in British Columbia, Turkingtom & Aarssen (1983) reported that, "most rosettes are found solitary or in small groups of between two and seven". This type of vegetative spread is rather limited, however, and H. radicata does not form large, pure stands.

Flowering reproduction

H. radicata flowers from June to September, having two peak periods, a larger one in the early summer and a smaller one in the autumn (Salisbury 1964). Given favourable growing conditions, H. radicata grows and develops very rapidly and can produce flowering plants from seed in just two months, an ability that helps to make it a persistent and successful weed in turf.

The average plant produces a mean of around 22 inflorescences (capitula or flower-heads) per plant, although the range is wide and Salisbury (1942) found the number varies from 3-56/plant in an English meadow. The capitula are borne on several 15-60 cm, leafless, branching stems (ie scapes) per plant, each scape bearing numerous small bracts. The spring or early summer capitula are considerably larger than the autumn ones (Salisbury 1964). Each flower-head or capitulum contains around 50 strap-shaped (ie ligulate), bright yellow, bisexual florets, the outer ones coloured greenish or grey-violet beneath. The outer florets are longer than the surrounding involucral bracts or phyllaries of the capitulum. When flowers are ready to open, according to Percival (1950), at least one hour of bright sunlight is required to stimulate morning opening of the capitulum and its florets. However, while this may be true of other members of the genus, and especially of H. glabra (Smooth Cat's-ear), Salisbury (1964) claims that H. radicata opens in daylight, even when it is dull and cloudy. The inflorescences or capitula do not open if it is raining or the balance of rain and sun is more than 1/6 rain. Given warm sunny conditions, capitula stay open for around three to four hours after opening, but in cool, cloudy conditions, the inflorescences stay open for longer, for around six to seven hours (Percival 1950).

The florets are usually insect-pollinated (by bees, bee-flies, thrips and hoverflies), but they are capable of self-pollinating occasionally, under certain circumstances, either involving the activity of thrips within the capitulum, the opening and closing of the capitulum in response to local weather conditions, or the trapping of raindrops within the flower-head. Having said this, there definitely is an inherent degree of self-incompatibility within the reproductive system of the species (Hagerup 1954; Proctor & Yeo 1973; Turkington & Aarssen 1983).

Seed is set from July onwards. Salisbury (1942) estimated an average of 44 achenes per capitulum and a production of about 970 wind-dispersed achenes per plant in England, while in a study in British Columbia the average was calculated as 2,330 (Ho 1964). There is clearly a great deal of variation in achene (or seed) production depending upon local growing conditions.

As is often the case in members of the Asteraceae, despite the achene possessing an attached hairy pappus, wind dispersal is not all that effective, the distance travelled by the vast majority of achenes in this case being less than 200 cm from the parent plant. Birds and ants are also believed to assist in the dispersal of the achenes to some extent (Ridley 1930). Evidence provided by the spread of the species worldwide strongly suggests that H. radicata was carried and accidently introduced as a contaminant of crop or pasture seed mixes.

Germination occurs throughout the growing season with peaks in the spring and autumn. Salisbury (1942) found that percentage germination again shows a wide range of variation, from as low as 33% to over 90%, so that the mean reproductive capacity is probably around 600 potential offspring per plant per year. Roberts (1986) believed that no persistent soil seed bank is formed, but the survey of NW European soil seed banks found a total of 22 estimates of buried seed longevity, 13 of which regarded it as ephemeral (ie survived less than one year), five considered it short-term persistent (ie survived for one–five years), one estimate regarded it as long-term persistent (ie at least five years), and three studies found seed buried but could not assign it to one of the other three categories (Thompson et al. 1997).

Hybrids

H. radicata can form short-lived, intermediate F₁ hybrids with H. glabra where they co-occur, but this is a rarity and has never been recorded anywhere in Ireland or Scotland (Stace et al. 2015).

British and Irish occurrence and status

Although H. radicata is generally assumed to be a native plant in the British Isles, its natural habitat is uncertain. Since the earliest definite B & I fossil is from the Roman period (Godwin 1975, p. 351) and in view of its extremely rapid invasion of countries where it has definitely been introduced (eg in New Zealand around 1860) it is difficult or impossible to be absolutely certain of its true status here (Turkington & Aarssen 1983).

European and world occurrence

H. radicata is a very variable species, widely dispersed as both a native and an introduction throughout most of Europe except the N and E, although it reaches almost 63^oN in Scandinavia, but only in coastal sites. Further south in warmer parts of Europe, it becomes distinctly Subatlantic-submediterranean in its occurrence, probably becoming limited by high summer temperatures and prolonged drought. It is also regarded as native in temperate parts of N Africa and Asia Minor (Turkington & Aarssen 1983). Hultén & Fries (1986, Map 1882) remark that, "It is most frequent towards W Europe.".

H. radicata has also spread to other cool, temperate parts of the world, including S Africa, N & S America, S Australia and New Zealand, where it is one of the most widely distributed introduced weeds in the country, occurring on a wide range of habitats including on sand dunes, railway ballast, riverbeds, swamps (most unusual) and in "damaged" forests (presumably opened up to allow adequate light penetration) (Webb et al. 1988). In Canada, H. radicata has also been found growing in an interesting mix of habitats ranging in moisture from dry to mesic and wet sites, including sandy slopes, gravel beaches, rocky shores, rock outcrops and wet decomposed peat (Turkington & Aarssen 1983).

Weed control measures

Cat's-ear can be controlled by ploughing or by other tillage and cultivation of the ground for a year or two before reseeding. Alternatively, it may be suppressed in permanent grassland by application of organic or inorganic fertilisers. In lawns, plants dug out below the crown or in early spring are effectively controlled. (N.B. the crown extends 2–3 cm below the ground surface.) The species is resistant to some common herbicides and an up-to-date edition of the Weed control handbook should be consulted if this option is preferred (Turkington & Aarssen 1983; Tu et al. 2001).

Uses

The leaves are edible and can, like many other members of the family, be used as salad or vegetable in soups and stews (Mabey 1972).

Names

The genus name 'Hypochaeris' was a name used for an unknown plant by Theophrastus, but the origin of the word is considered doubtful by Gilbert-Carter (1964). Stearn (1992) also casts doubt as to which genus Theophrastus applied the name. The Latin specific epithet 'radicata' means 'having a large root' (Gilbert-Carter 1964).

The English common name 'Cat's-ear' is said by Prior (1879) to refer to the leaf shape, but Britten & Holland (1886) dismiss it as being, "a common book-name, rather than such as are in the mouths of the country people". The first British Isles record for the species appeared in the first edition (1597) of John Gerard's Herball, where it was named Hypochaeris longius radicatum, and described as being found, "in untoiled places …".

Threats

None.

References

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