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Conopodium majus (Gouan) Loret, Pignut

Account Summary

Native, common and very widespread. Oceanic temperate and tightly restricted to W Europe.

1881; Stewart, S.A.; Co Fermanagh.

Throughout the year.

Growth form and preferred habitats

This tuberous perennial, up to 8-70 cm tall, has glabrous, stems and leaves and displays a short, vernal season of growth and reproduction (Grime et al. 1988, 2007). The basal leaves of the plant are 2-4 times larger than the stem leaves and are borne on a petiole 4-15 cm long. The leaf blades of the basal leaves are 2-pinnate, but they do not long survive, withering by late spring or early summer, so that they often are completely absent when the plant flowers in May and June. The stem arises from an irregular, dark brown, nut-like subterranean tuber, 8-35 mm in diameter, which is deeply buried. The tubers are edible, raw or cooked, and are described as having a pleasant, nutty flavour (Tutin 1980). Nowadays, for conservation reasons, it is forbidden to dig up wild plants, the only exception being the landowner. The stem bears 2-4 leaves, each with a well developed greenish membranous sheath at its base and a reduced petiole. The ultimate lobes of the stem leaves are elongated and linear and the terminal lobe is much longer than the lateral lobes (Tutin 1980; Jonsell & Karlsson 2010).

C. majus is a very characteristic stress tolerant ruderal (SR) species of damp or shaded ground in woods, scrub, heaths, shaded cliffs and in a wide variety of mesic agricultural grasslands (Grime et al. 1988, 2007). It is particularly frequent in relatively infertile soils derived from limestone, but occurs in both moderately acid and base-rich situations, most frequently in the pH range 4.5-7.0. It also appears under similar growing conditions on relatively undisturbed, unproductive grassy roadsides and in waste ground. It is said to be scarce on chalk in England (Grime et al. 1988, 2007).

Flowering reproduction

Despite the production of vegetative subterranean tubers, reproduction is entirely dependent on seed. The plant flowers early in the season, in May and June. The inflorescence is a compound umbel, 5-8 cm wide, with 6-12 smooth rays, the peduncles longer than the rays. Flowers, 16-24 per 'umbellule' (ie ultimate or secondary simple umbels), with a total flower count of >50 per complete inflorescence; petals white, outer ones not or scarcely radiating. As is normal in the Family Umbelliferae (or Apiaceae), a proportion of the flowers are staminate (ie entirely male). In C. majus, staminate flowers form the majority, only one in five being hermaphrodite (ie bisexual or perfect) (Lloyd 1979 unpublished; quoted in Lovett-Doust 1980). Nectar is well exposed and pollination is by insect visitors including bees and wasps (Proctor & Yeo 1973). The crowded nature of the numerous flowers in umbels favours a mixture of self- and cross-pollination (Lovett-Doust 1980).

The fruit is c 4 mm long, ovate in outline, slightly flattened laterally and dark brown in colour and is formed and ripens in June and July. By the time seed (the twin mericarps) is produced, the aerial stem is already dead and it soon disappears, the plant overwintering as both buried vegetative tubers and seed.

Seed germinates early in the year after its production, between January and March following a dormancy-breaking chilling period (Roberts 1979). In an experimental study of 121 specimens, the mean number of mericarps produced per plant was 215.5 ± 9 with a range of 40-958 (Salisbury 1942). Seed survival in soil is transient or short-term persistent (ie they persist for at least one year, but for less than five) (Thompson et al. 1997).

Fermanagh occurrence

It is very common and widespread in Fermanagh, having been recorded in 326 tetrads, 61.7% of those in the VC. Pignut appears ± everywhere throughout the county, except on strongly acidic peat, regularly wet ground or heavily grazed pastures.

Cotyledons and fundamental biological concepts

C. majus is one of the few dicotyledonous species that actually produces just one embryo seed leaf, the other presumably being suppressed or aborting early in its development (Metcalfe 1936; Grime et al. 1988, 2007; Thompson 1988). It is not unique in this respect: the same is true of the quite closely related species, Bunium bulbocastanum (Great Pignut), plus in other families, Ranunculus ficaria (Lesser Celandine) and some Corydalis spp. (Thompson 1988). This observation should forcefully remind us that even the most fundamental and revered biological concepts, like this example linking us back to the work of the great John Ray (1627-1705), may be somewhat 'leaky' (Morton 1981, p. 203; Raven 1986, p. 189). There are 'natural laws' in physics, but none in biology. Our description of the natural world and the categories we use to subdivide and label organisms and ideas are often a convenient over-simplification of the variation and subtleties that really exist (Proctor et al. 1996, p. 330; Forbes 2000). It is fundamentally important that as scientists we recognise that the plants we study have not read the books, and when we read any material, no matter how much we respect the author, we should never assume that everything printed is infallible 'holy writ'. As the current author's mother (Jean Forbes) occasionally used to remind him, "pen, ink and paper refuse nothing".

Herbivory

Due to its vernal phenology and short photosynthetic period, C. majus is very susceptible to heavy grazing pressure in the spring. Badgers commonly dig up the globular brown Pignut tubers and in some areas of B & I they are an important part of their diet. Even recently weaned badger pups have been observed digging for them (Neal & Cheesman 1996). In Speyside, in Scotland, the tubers represented 14% of the badger's summer diet; they dig as deep as 40 cm, but no lower. Badgers dig for the tubers when the plants are flowering, probably because they are unable to detect them in winter (Kruuk 1989).

British and Irish occurrence

Common throughout most of Britain, but absent from the English Fens and scarce on chalk soils. It was introduced in Shetland in the 19th century, but its status on Orkney is uncertain. It is less common in Ireland, but especially so in the area of 'the English Pale' around Dublin, where agriculture is most intensive, and in the far west coastal areas where soils are most likely too wet and too acidic (M. Southam, in: Preston et al. 2002).

In Britain, the recent BSBI Local Change survey of 1987-2004 showed that C. majus has suffered a widespread, statistically significant decline in recent years: when the species distribution was examined at the tetrad level the weighted Change Factor calculated was -23. Most probably the decline is due to grassland 'improvement' measures, involving the ploughing up, reseeding and fertiliser and herbicide spraying of old grasslands, plus a widespread move from hay- to silage-making (Braithwaite et al. 2006).

There are no comparable data to suggest that Pignut is suffering any decline in Fermanagh, but since similar agricultural grassland management changes have been applied locally in lowland areas of the county, it is quite likely that some decline in population size and frequency must have occurred.

European and world occurrence

C. majus belongs to the Oceanic Temperate biogeographic element and is confined to W Europe from Norway southwards and eastwards to NW Italy (Sell & Murrell 2009). The map prepared by Hultén & Fries (1986, Map 1392) shows C. majus very much confined to western oceanic parts of Europe, extending from the Faeroes to N Morocco and east as far as Corsica, although absent from Italy. Pignatti (1997) plots the species as present in two districts of NW Italy in or near the Maritime Alps. The text associated with Hultén & Fries map indicates they believe C. majus is introduced in the Faeroes and in Germany, and suggests "probably [introduced in] more places" (Hultén & Fries 1986).

The current author (RSF) suggests the means of introduction is almost certainly seed, transported either as a contaminant in commercial grass seed mixtures, or in hay, a form of fodder that has become much rarer than previously was the case, having been replaced by silage and manufactured 'nuts'.

In parts of Scandinavia (including Denmark), C. majus was introduced either as a minor root vegetable, or later as a grass seed contaminant. The species is often only casual in Scandinavia, although it forms large, dense populations in W Norway in open fields and pastures along the coast (Jonsell & Karlsson 2010).

The current author (RSF) is sceptical about the extent to which the tuber was used as food, since it is generally small in size and would be difficult to gather in sufficient quantity to make a meal for more than one individual. Also, C. majus apparently does not lend itself to garden cultivation and horticultural improvement despite 18th century trials to that end which found, "the Earthnut will not thrive in tilled land" (Bryant 1783).

Names and uses

'Pignut' and 'Earthnut' are only two of 38 English common names and variants listed by Grigson (1955, 1987), both of which refer to the small, but edible underground tuber of the plant. Similarly, Vickery (2019) has a count of at least 50 English common names indicating great familiarity with the species. However, the derogatory connotations of some name elements such as 'pig', 'fare' in 'Farenut' ('fare' is a young pig, from the Old English 'fearh'), 'hog', 'swine', 'scabby', 'lousy', 'hare', 'cat', 'devil' and 'jack', all suggest a degree of contempt or dislike for the plant and its use, similar to that noted for Anthriscus sylvestris (Grigson 1955, 1987) (see that account on this website). The digging and eating of the tubers is described by Vickery (2019) in terms of children's play and he makes no mention of any other associated folklore.

There is very little evidence of use in herbal medicine and it is not mentioned at all in modern herbals by Grieve (1931) and Darwin (1996). It is said to have been employed as a diuretic on the Isle of Man, for cleansing the blood in Co Donegal and as a tea substitute in Co Fermanagh, although it is not known if this was considered medicinal or not (Allen & Hatfield 2006).

Threats

None.