Lotus corniculatus L., Common Bird's-foot-trefoil

Account Summary

Growth form and preferred habitats

This as a low, sprawling, sometimes carpet-forming, usually almost hairless, bright-yellow flowered perennial legume with solid spreading stems, round in cross-section at their base but square higher up. It is readily distinguished from the most commonly found related species, L. uliginosus Schkuhr (= L. pedunculatus Cav.) Greater Bird's-foot-trefoil, by its solid rather than hollow stem and its calyx teeth that are appressed to the corolla in bud, rather than spreading (Webb et al. 1996).

L. corniculatus is common and locally abundant throughout B & I in unshaded situations on short pastures and on dry to wet grassy places on a very wide variety of soils. These include those formed over both limestone and more acidic rocks, of sandy, clayey or peaty texture, and including very infertile situations on damp upland moors and wetter Sphagnum bogs. Common Bird's-foot-trefoil produces its most vigorous growth on moist, heavy, fertile, lime-rich soils of pH around 6.5 (Smith 1975; Turkington & Franko 1980).

Particularly in drier grassland conditions or in rock crevices, the plant develops a deep, robust taproot up to 100 cm long, with numerous laterals. This penetrative organ, which becomes thick and woody with age, allows the species to survive drought for several weeks. In wetter soils and those subjected to water-logging for 1-3 months or more, the 'rootstock' is short and thick, with the dense fibrous lateral roots being retained near the soil surface. The rootstock is a long-lived organ enabling perennation, since the aerial parts generally die down and become quite limited or entirely absent in winter. Die-back to a small rosette in the late autumn allows the new buds for next spring's growth the shelter and protection of the dead stems (Jones & Turkington 1986). The extensive root system explains the frequency of the plant on dry rocky soils, eg screes, quarries and cliff ledges. When occurring in coastal or inland sandy soils, the deep roots help stabilise the substrate, enabling the frequently observed large colonies to develop.

In meadows and pastures, the plant is favoured by regular cutting or grazing which reduces competition from taller, more vigorous grasses and herbs, although L. corniculatus is capable of surviving and being drawn up to some extent with inherently taller species (Jones & Turkington 1986). Common Bird's-foot-trefoil has a weak stem and growth with a companion grass in pasture leys provides support and prevents lodging. It does particularly well with slow-establishing grasses such as Phleum pratense (Timothy), which offer less intense competition at the seedling stage. Seedlings of Common Bird's-foot-trefoil are small, non-aggressive and slow-growing and are thus easily out competed. While it is light-demanding, L. corniculatus is otherwise decidedly stress-tolerant and rather uncompetitive. Grime et al. (1988) categorised its established strategy as intermediate between a stress-tolerator and C-S-R, a balance which really is non-committal on this issue.

However, when growing in infertile, species-rich grasslands or heaths, this legume, being self-sufficient in nitrogen and with its extensive root and shoot system, can manage to co-exist with up to 35 other plant species (Atkinson 1973). In pastures in N America, once established, it can withstand heavy grazing and does not cause bloat in grazing animals, as do most other legumes (Smith 1975). The feeding value of Common Bird's-foot-trefoil in silage or hay has been reported as equal or surpassing that of alfalfa and other good legume hays when fed to dairy cattle and sheep (Marten & Jordan 1979).

While it is always absent from shade in woodland or scrub, once established it can persist in more open, marginal or disturbed areas of these habitats, as well as in lower-growing, woody heath vegetation.

Flowering reproduction

Regeneration of this long-lived herb is primarily by seed, produced in large numbers after cross-pollination by bees. Nectar can only be obtained by long-tongued insects of sufficient weight and strength to open the pea flower and cling on to it. Unlike many other pea-flowers, the fused keel petals do not open, and a peculiar 'pumping arrangement' is used to effect cross-pollination. Before the flower is visited, pollen is discharged into the conical tip of the fused keel petals and held there by the elongated club-shaped filaments of the five outer stamens. When the bee lands on the flower, its weight pressing on the wing and keel petals acts like a piston on the contained stamen filaments, which press forward and squirt the somewhat sticky pollen like a worm-like pasty mass through a very small hole or slit in the apex of the keel, to form a small coil of pollen that sticks to the hairy lower part of the insect's abdomen. Later on, the stigma emerges from the tip of the fused keel petals and rubs on the abdomen of a subsequent bee visitor (Hutchinson 1972; Proctor & Yeo 1973). Pollen-collecting bees are said to be more effective in pollination than nectar-collecting bees (Bader & Anderson 1962). Self-pollination can occur, but experimental evidence showed it only occurred in 53% of flowers, of which 46% set 0.01-0.49 seeds per flower and 7% set just 0.50-1.0 seeds per flower (Seaney 1964). In other studies, wild collected British flowers were found to be totally self-sterile (Ramnani 1979).

Flowering begins in late May, reaches a peak in June and July and continues into August. In some situations, a second flush of flowering takes place from mid-August to mid-October. The flowers, 15 mm long, are borne in cymose clusters of 2-6 (usually five) on erect peduncles 3-10 cm tall. The corolla varies in colour from bright yellow to coppery or brick red and the standard petal is often streaked with red lines. Frequent flower-shedding, and the failure of many flowers to develop seed pods, set limits to seed-production capacity of the species (Bader & Anderson 1962).

Fruits develop from late June onwards. The cylindrical ripe pods, five or six together, are brown to blackish, 15-30 mm long and each is tipped with the persistent style, making them together look like the claws of a bird's foot and hence the English common name. Each pod contains between 1-20 seeds (mean 5.9) that are explosively released from the ripe legume when it suddenly splits along two sutures and twists violently to eject the seeds. Measured as seeding distance from the parent plant, the mean dispersal distance was 0.24 m and the maximum achieved was 1.75 m. Seed per plant can vary enormously from zero to over 18,000 depending upon site and season (Jones & Turkington 1986). Seeds germinate in the spring, but a portion of them may persist in the soil seed bank for at least five years (Thompson et al. 1997). The seeds are sufficiently 'hard' (ie water impermeable) that they can pass through the digestive tract of sheep, cattle and birds unharmed (Grant 1967).

L. corniculatus is one of the few legumes that can produce adventitious buds and shoots from the root when the crown is removed or the root sectioned (eg by cutting, grazing or heavy trampling) (Smith 1975). Thus plants in some habitats may be capable of displaying a limited degree of vegetative reproduction through rooting of older, horizontally spreading stems (Jones & Turkington 1986).

Variation

L. corniculatus is tetraploid (2n=24) and is the most variable species in the entire genus of around a hundred species, displaying both great morphological and physiological variation, some of which is genetic. The species is important as a legume in grass seed mixtures in agronomy in the making of silage and hay, and many named varieties have been developed by plant breeders, particularly in the USA and Canada since the 1950s (Turkington & Franko 1980). The cultivars tend to have an upright habit, unlike the more usual prostrate native forms of the species.

In Britain, the species gives rise to up to eight named varieties (Ellis et al. 1977; Jones & Turkington 1986; Sell & Murrell 2009), although Stace (2019) ignores them all except the distinctive introduced, weedy, roadside var. sativus Hyl. which is up to 50 cm tall, has large leaflets and small flowers.

Toxicity

The leaves and flowers of some L. corniculatus genotypes are cyanogenic at levels sufficient to discourage species of molluscs and other selective herbivores (Ellis et al. 1977). However, numerous insects and their larvae have adapted to cope with the toxins. Jones & Turkington (1986) published a four page list of insects that feed on the plant.

Fermanagh occurrence

L. corniculatus has been recorded in 244 tetrads, 46.2% of those in the VC. As the Fermanagh distribution tetrad map indicates, however, it is unevenly scattered in the VC, being most prevalent in damp grasslands around Lough Erne and on the limestones of the upland Western Plateau.

British and Irish occurrence

The New Atlas hectad map shows that this is one of the most omnipresent legumes on both islands, there being very few hectads where it has not been recorded.

European and world occurrence

The species is native and occurs almost throughout Europe to 71°N and to an altitude of 3050 m in the Swiss Alps, but it is absent from Spitsbergen. It has been introduced to Iceland. It is also indigenous in coastal N Africa and in parts of Asia. As it has been quite widely used as a forage crop for cattle in Europe since the 18th century and in N America since the 1950s, and also commonly occurs as a seed impurity of White Clover (Trifolium repens) and low-grade grass seed, it has been widely spread by man well beyond its native range. In Canada, it is classified as an adventive, ie introduced but imperfectly naturalised (Turkington & Franko 1980). It is introduced in E Africa (eg Ethiopia and Kenya), very widely in N America and to a much lesser extent in S America, plus in S Australia and New Zealand (Turkington & Franko 1980; Hultén & Fries 1986, Map 1249).

Names and folklore

Although there is very little folklore associated with Common Bird's-foot-trefoil (Vickery 1995) and it does not appear to have much in the way of herbal uses either (Allen & Hatfield 2004), it does have a huge number of folk names attached to it. Grigson (1955, 1987) list over 70 names and even he finds it difficult to explain this fact. In ancient herbal use, it was considered another vulnernary wound-healing herb, but the only more modern use traced by Allen & Hatfield (2004) was as an eyewash on South Uist in the Outer Hebrides. It does not feature at all in Grieve's (1931) comprehensive herbal. In Irish folklore, in the south of the country, children called it 'No blame' and regarded it as worth collecting and bringing to school as a protection from the teacher's cane (Vickery 1995).

Threats

None.

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