Jasione montana L., Sheep's-bit

Account Summary

Growth form and preferred habitats

Typically a biennial (but see below), or a short-lived, monocarpic perennial, very rarely an annual, J. montana produces a very distinctive basal rosette of hairy, hispid, bristly, undulate, spoon-shaped leaves, which, like other aerial parts of the plant and other members of the Campanulaceae family, exude white latex when broken and squeezed, and thus the species is recognisable in the non-flowering state throughout the year. The stem leaves are alternate, making a useful distinction from Devil's-bit Scabious, Succisa pratensis, with which the flower heads could readily be confused. The latter species also has much larger, hairless, oppositely arranged leaves so the two are very easily distinguished. The tight packing of the Sheep's-bit basal rosette is such that the leaves shade one another (ie self-shading occurs), reducing the photosynthetic ability and limiting the growth rate and reproductive performance of the plant (Parnell 1985).

J. montana has a strongly marked, but not exclusive western distribution in Britain (BSBI Atlas 2; New Atlas). In Ireland, it is almost entirely restricted to heathy, well-drained or shallow acidic soils at the coast or just inland of it, or on base-poor, freely draining soils in mountainous or at least upland areas. The habitats where it is most frequently found in B & I include sea-cliffs, rock faces, sand dunes, maritime heaths and inland on mountain cliffs, hedge banks and walls, although it has to be said it has a low constancy rating in all of these habitats (Rodwell et al. 2, 1991b, 5, 2000).

J. montana also occurs very rarely as a weed of disturbed soil, burnt ground and waste places adjacent to the other habitats already mentioned (Parnell 1985). Sheep's-bit is only rarely encountered in more central Ireland, but it should be remembered that almost all the higher hills on the island of Ireland are at or close to the coast. 

Variation

There is a great amount of phenotypic plasticity with response to environment and geography present in J. montana, reflected in variation within a large number of morphological characters and performance, leading to recognition of named subspecies and varieties. A total of five varieties and a subspecies are recognised across Europe, two of which occur in B & I, namely var. latifolia Pugs. and var. litoralis Fr.

J. montana var. latifolia grows in hedgerows and on exposed cliffs in SW Britain and E Ireland. It is characterised by its robust stature, involucral bracts that often protrude beyond the flowers, extremely stout peduncle and upper leaves on the peduncle often larger than 20 × 5 mm. J. montana var. litoralis grows exclusively on sand dunes and is characterised by its decumbent, highly branched habit (Parnell 1985).

Fermanagh occurrences

In land-locked Fermanagh, there are only two unconfirmed field records for Sheep's-bit. Both of these are derived from botanical survey work carried out in 1986 by the DOE(NI). Fortunately, the two field recorders involved are experienced and reliable, so that the current author (RSF) and RHN have some degree of confidence in the veracity of their two records. However, in order to be official BSBI First County Records, they require supporting voucher specimens, and since everyone is capable of a slip of the tongue, or momentary mental fumble with pen and paper, both records could simply be rare examples of field errors. The first record is given above and the second station was at Kilnameel Td, 2 km S of the limestone Marlbank area, where Shaun Wolfe-Murphy recorded it in a quadrat sample on 25 June 1986.

It is interesting that the plant has been recorded in the Knockmore and Marlbank calcareous areas of the VC, since normally the species avoids limestone. It is, for example, totally absent from the karst Carboniferous limestones of the Burren, Co Clare (H9), although it is frequent and locally abundant elsewhere in S Clare and in Connemara immediately to the north of the Burren (mainly H16) (Flora of Connemara and the Burren).

The New Atlas hectad map shows the presence of the species in Co Sligo (H28), which shares the same geological limestone structure as Fermanagh, but the type of site and soil needs to be checked to see if a parallel really exists (T.D. Dines, in: Preston et al. 2002).

Although perfectly familiar with the species from its common occurrences in coastal sites, none of the authors of the two Fermanagh Floras, Meikle and co-workers or and RSF and RHN, have ever seen the species growing in Fermanagh, so it certainly must be extremely rare in the VC.

British and Irish occurrence

As already mentioned, J. montana has a predominantly western and coastal distribution in B & I, although the western emphasis is less marked in Ireland. The distribution in Scotland is rather odd, the species being almost confined to the W coast, petering out just north of Oban, absent from the NW isles, but then reappearing and becoming widespread in Orkney and Shetland. Populations in Scotland and inland throughout B & I tend to be small and the number of populations appears to be declining. However, elsewhere in these islands, for instance in S England, and in coastal areas of Wales, Ireland and the Isle of Man, the species can still be abundant (Parnell 1985).

It is not easy to identify the factors producing the observed B & I distribution of Sheep's-bit. Temperature and rainfall can both be correlated with the pattern. In B & I, the species is mainly confined to areas which receive over 1500 mm annual precipitation, and where the average annual minimum is usually above minus 6^oC, and, in Britain, where the February minimum temperature is 1.5-2.5^oC (Parnell 1985). In addition, Kolstrup (1980) found that J. montana serves as an indicator of a minimum July temperature of 11-12^oC. The northern limit in Scandinavia is found in coastal areas which experience at least 100 days without coherent snow cover, thus exposing the plants to conditions of severe frost (Parnell 1985).

Flowering reproduction and the biennial lifestyle

J. montana reproduces entirely by seed, the plant flowering from late May to August. The disc-like inflorescence contains a tight, domed cluster of around 40 pale blue florets, the plant generally producing five long-stalked flower-heads per plant. As with other so-called 'biennials', plants of J. montana appear to have a minimum rosette size as a requirement for flower initiation. The current author (RSF) believes the concept of a 'biennial' reproductive strategy is a horticultural construct, which when applied to wild populations often leads to an inaccurate and misleading picture of what really happens in 'wild nature', ie in semi-natural vegetation beyond the garden wall. Harper (1977) commented, "It is a serious error to regard the biennial habit as anything but an ideal horticultural practice.".

Under cultivated conditions, biennials are essentially monocarpic species (ie they fruit just once). Plants with this strategy germinate and in their first growing season develop a vegetative leaf rosette which accumulates surplus energy as starch in a substantial underground storage organ. As anyone who has ever gardened knows, this plant individual then perennates, becomes dormant and rests overwinter. In its second spring or summer, it has sufficient stored energy resources to enable successful flower, fruit and seed production and this proceeds and generates garden colour. Individuals of monocarpic species, however, carry their biological parenting (especially the male sexual selection element of it) and their genetic responsibilities to future generations to the absolute extreme. In the same way as annual plants do in just one season or in a part thereof, monocarpic plants which have successfully overwintered proceed to expend so much of their accumulated energy resources on the production of flowers and seed, that in completing their first reproductive-cycle they completely exhaust their photosynthetic resources. Thus they are no longer equipped to survive a subsequent overwintering period and equally, and importantly, they forego the chance of producing any vegetative propagules. After fruiting once they simply die off.

Richards (1997) has aptly described the monocarpic reproductive strategy as following a line of directional selection, which he says, "seems to have proceeded to this logical but rather ludicrous extreme". He likens the evolution of monocarpic plant behaviour to the antlers of the extinct Giant Irish Elk, or to the Peacock's tail in the zoological realm (Richards 1997a, pp. 39-40).

In the artificial, managed, cultivated garden setting, where the basic growth requirements of the individual plant are fully met and where competition with neighbours is reduced to a minimum, this type of seed-dominated life-cycle consisting of more than one growing season, normally occupies just two seasons, and hence the species is described as being a biennial. Under the much less ideal habitat conditions of semi-natural vegetation, many such plants require three, four or more year's growth before they accumulate sufficient stored energy resources to reach a threshold which allows other influences such as day-length and temperature to trigger flower initiation and sexual reproduction. Thus so-called 'biennials' growing beyond the garden wall, as J. montana generally does, are often best considered, short-lived monocarpic perennials. Other common examples of biennials that require more than two years to flower in the wild include Dipsacus fullonum (Wild Teasel), Pastinaca sativa (Wild Parsnip), Senecio jacobaea (Common Ragwort) and Verbascum thapsus (Great Mullein).

Delayed reproduction is favoured and selected for when seed production increases disproportionately with the length of the delay. In habitats where intermittent disturbance is a feature of the vegetation, short-lived monocarpic perennials are at an advantage over annuals, as the latter require gaps in vegetation every year in order for their seed to germinate, establish, flower and fruit: without annually available space, annuals are unable to produce a new generation every year and thus they lose their advantage over short-lived monocarpic perennials (Silvertown 1984).

Further studies have indicated that a distinction can be made between 'strict biennials' and 'facultative biennials', the former with a definite two-year life-cycle, including Linum catharticum (Fairy Flax) in calcareous grassland in N England, Pedicularis palustris (Marsh Lousewort) and P. sylvaticus (Lousewort) in sand-dune areas in Holland, Melilotus albus (White Melilot) in a limestone quarry in New York, Gentianella germanica (Chiltern Gentian) in a chalk grassland in the Netherlands and G. amarella (Autumn Gentian) near Cambridge, England (Kelly 1985). The 'strict' and 'facultative' biennial labels are useful to distinguish these short-lived perennials from other perennials that may live for hundreds of years. Strict biennials may be rare, but they do exist, perhaps principally in infertile or undisturbed habitats and their flowering is triggered by age rather than by plant size (Kelly 1985).

Flower structure and pollination

The flowers, 8 mm long in their tight inflorescence heads, 7-30 mm diameter have five sepals, small and united, calyx teeth linear and acute. The corolla is of five petals, lilac blue, free and oblong, but united at the base. The four stamens have their filaments and anthers free, but fused together at their bases (Melderis & Bangerter 1955). The ovary is inferior (below the calyx) and the style is slender. In the young stage, while still in bud, the end of the style is covered with closely set erect hairs. In the flowers of J. montana, nectar is secreted from the top of the ovary and this food reward, being openly presented and freely available, it attracts a very wide range of insect visitors, chiefly Hymenoptera (ants, bees and wasps) and Diptera (flies), but also beetles, butterflies and moths.

The five anthers shed their pollen (white, pink or purple in colour) in the flower bud long before the stigma opens (ie the flowers are markedly protandrous) and it is presented on the hairs of the young style, ie the 'stylar brush', typical of the family. [See the current author's Campanula rotundifolia species account on this website for details of this interesting floral mechanism.] The insect visitors, hungry for nectar and pollen, remove the latter efficiently and rapidly, often within one or two days of the flower opening. After the pollen has been delivered, the stigmas open out and become receptive to pollen (Hutchinson 1972).

Unusually for a monocarpic species, a very strong self-incompatibility mechanism exists (Richards 1997a, pp. 358-60) and out-breeding cross-pollination between different plants is greatly favoured, although pollination within the same inflorescence is also possible (Parnell 1982, 1985).

The mean seed number is six per capsule for flowers out-crossed between populations, so that the estimated reproductive potential on this basis is 1,200 seed per plant. As with many other aspects of performance in this species, the actual number is very variable with respect to both genetic variety and individual growing conditions. Parnell (1985) reported mean seed production for four Irish populations of var. montana that ranged from 349-2,367 per plant.

The fruit capsule consists of two valves which split apart at the top to release the seed, the period of fruit and seed ripening after pollination taking anything between two weeks and three months! The seeds are very small, measure 0.8 × 0.3 mm and are ellipsoid, smooth, keeled and shining brown (Butcher 1961; Hutchinson 1972). There is no specialised seed dispersal mechanism and the normal maximum seed travel is only around 1.4 m from the parent plant.

The soil seed bank has been very little studied, but what evidence there is suggests it is only transient, most seed germinating either one or two weeks after release, or after a six month delay (Parnell 1985; Thompson et al. 1997).

Tolerance of grazing and other pressures

The tight rosette form and bristly hairs on the leaves perhaps offer the plant some physical protection from grazing animals but, in addition, while not described as poisonous, the plant also contains at least two alkaloids which may make it somewhat unpalatable. While the plant contains latex which oozes in a conspicuous manner when the plant is damaged, no evidence of cyanogenic activity has been detected. Parnell (1985) found conflicting evidence and reports on the herbivore pressure from widely dispersed regions of the British Isles and he concluded that the species was, "moderately susceptible to grazing". On the other hand, Sinker et al. (1985), for example, regarded J. montana in the Shropshire area as being tolerant of trampling, grazing and drought, and in addition it was considered a poor competitor with taller plants, though it can tolerate partial shade for a time.

Fossil history: The early fossil record for Jasione montana is decidedly sparse, with just one Hoxnian and one Ipswichian Interglacial record known. Later records are, however, widely spread across the British Isles and indicate prevalence in the Late Weichselian ice age, and possible subsequent persistence (Godwin 1975, p. 334).

European and world occurrence

In Europe, J. montana has extensive populations in most W, C & E countries, becoming less frequent northwards and reaching a limit at 62^oN in Finland, and with an eastern limit in Russia at around 53^oE. In the Mediterranean basin, it is confined to the western end and while present on the larger islands (Corsica, Sardinia & Sicily), it is absent from the Balearic Isles. Beyond Europe, it is known from coastal NW Africa, but not from Libya or Egypt. Sheep's-bit is a common naturalised introduction in NE North America, and has also become established in British Columbia and New Zealand (Parnell 1985; Hultén & Fries 1986, Map 1762).

Names

The genus name 'Jasione' was an ancient Greek name 'iasome'(?), meaning 'healing' or possibly 'healer', used by Theophrastus and applied not to this plant at all, but to Calystegia sepium (Hedge Bindweed) or some other member of that family, or possibly to another unknown medicinal plant (Melderis & Bangerter 1955; Gilbert-Carter 1964; Chicheley-Plowden 1972). The Latin specific epithet 'montana' is obviously, 'of mountains', and thus fails to give the whole habitat picture.

Sheep's-bit Scabious and Devil's-bit Scabious (Succisa pratensis) (both sometimes referred to without the 'scabious', which anyway is erroneous when applied to Jasione, since it belongs to the Campanulaceae), have a passing resemblance, and the two may grow adjacent to one another in coastal sites. J. montana always grows on the drier ground of the two. They also share some alternative local English common names, for instance, 'Blue bonnets' and 'Blue buttons', while J. montana is also referred to as 'Blue Daisy', 'Blue Cap' and 'Iron-flower' in the Cheshire area (Grigson 1955, 1987).

Sheep's-bit is an eighteenth century 'book name' derived from Lyte (1578), who presumably wanted to distinguish the flowering plant from the superficially similar Succisa pratensis and, therefore, called it 'Sheepes Scabious', since it grew on barren hillsides rather than in cornfields and was, therefore, grazed by sheep (Prior 1879; Grigson 1974). It is difficult to see the origin of the name 'Iron-flower', but it might possibly be linked with 'Iron-heads', a name commonly given to Centaurea nigra (Common Knapweed), said to be due to the resemblance of its knob-like inflorescence to a Mediaeval weapon with an iron ball fixed to a long handle, called a 'Loggerhead' (Prior 1879). As a child, RSF recalls playing a conker-like game with Centaurea nigra, trying to knock the head off an opponent's peduncle, and perhaps the same game was played with Jasione stems in other areas of the country.

Threats

None.

References

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