Euphrasia micrantha Rchb., Slender Eyebright

Account Summary

Growth form and preferred habitats

This annual, up to 60 cm tall, but often shorter than this and with spreading branches and opposite, entire, narrow leaves is a partial- or hemi-parasite on the roots of an accompanying range of plants, including trees, ericaceous sub-shrubs and Myrica gale (Bog-myrtle). It is not absolutely clear if it can use herbaceous plants, especially Deschampsia flexuosa (Wavy Hairgrass), with which it is often associated, as hosts, but in many situations it exclusively parasitizes woody plants (Smith 1963; Masselink 1980). M. pratense is an extremely variable plant, the leaves often bronze-green to chocolate brown and the petal colour varying from pale yellow-white to a rich, bright yellow like a buttercup.

The established strategy of M. pratense is categorised as R/SR, meaning it is intermediate between a straightforward Ruderal and a Stress-tolerant Ruderal (Grime et al. 1988, 2007). The semi-parasitic nature of this annual requires the seedling plant, produced after autumn germination, to send out sufficient roots of its own in order to locate the roots of a suitable host plant, attach and create an effective haustorium linkage. If this aim is achieved, it enables the plant in the spring (around March-time), access to the nutrient support essential to its further growth, development and reproductive survival. Without host plant contact and support, the juvenile M. pratense plant remains undeveloped and it gradually withers away during May and June (Smith 1963). After flowering and fruiting, the plant dies in late summer or autumn (Masselink 1980).

The advantage hemi-parasitism gives M. pratense plants is the ability to grow very rapidly in environments with exceedingly low nutrient soils that severely limit the competitive ability of any other vascular plants present. M. pratense reaches full size and reproductive capability after a few weeks' growth and, in nutrient-deficient habitats, this feat is only possible if a substantial proportion of its nutrients and moisture requirement are obtained from its host plant. M. pratense is a shallow rooted species, but observation in drought conditions shows it is able to obtain a fully adequate water supply from the host plant, making it independent of soil water (Smith 1963).

As is often the case elsewhere in B & I, M. pratense usually occurs in small, isolated populations of around 200 plants (Smith 1963). It is locally frequent, but rarely abundant, in a strikingly wide range of habitats in Fermanagh, encompassing acidic (preferred) and calcareous, nutrient-poor, wet but drained or dry soils in both semi-shaded and more open situations.

The species is clearly bimodal with respect to soil reaction, occurring on both acidic soils of pH down to 5.5 and limestone or chalky ones of pH 6.8 or more (Smith 1963). The habitats colonised include woodland waysides, clearings and margins, lakeshores, peat bogs, upland heath and limestone cliffs. In N Scotland and N England, it also occurs in boggy flushes and waterlogged peat in acid bogs (Smith 1963; Garrard & Streeter 1983). M. pratense does seem to be more frequent today in heathland communities managed using fire to regenerate and keep them from senescing (Ingrouille 1995). Interestingly, in the Netherlands, M. pratense does not occur in heath vegetation (except those with Vaccinium myrtillus (Bilberry) and/or V. vitis-idaea (Cowberry)), or on peatlands or in conifer woods (Masselink 1980).

Flowering reproduction

Flowering takes place from May to October, the inflorescence consisting of a series of single flowers, 15-20 mm long, in the paired axils of the upper opposite, green, leaf-like bracts. However, the nodes are twisted, so the flowers are all turned to the same side to lie alongside one another (ie they are secund). The bi-lipped petal tube is closed or only very slightly open with a large yellow palate; nectar production is high. The four stamens are positioned with their anthers converging under the upper lip of the corolla forming a 'pollen box' into which the anthers shed their contents. Visiting bumble-bees probing past the anthers for nectar invariably unlock this box and get showered with pollen. This is known as the 'loose-pollen mechanism' (Melderis & Bangerter 1955). In addition to the floral nectary, the bracts at the base of the flowers and leaves close to them are provided with nectar-secreting hairs, acting as extra-floral nectaries that attract ants. The extra-floral nectaries are indistinct depressions on the leaves and bracts of M. pratense (Britton 1943; Hutchinson 1972).

If insect visits fail to occur, the flowers are selfed, since they are homogamous and the stigma is positioned close to the anthers (Clapham et al., 1962). Individual flowers may continue to function for up to seven days, which is unusually long in this flower family (Molau 1993).

The fruit capsule is obliquely ovate, compressed and splits along one side to release the maximum of four large, pale- to dark-brown, ellipsoid seeds, 3-5 mm long (Britton 1943; Butcher 1961; Hutchinson 1972).

Seed is shed from July to early September. The seed bears an oil-body (elaiosome) attachment derived from the funicle or stalk of the ovule. This, and the extra-floral nectaries that secrete a watery saccharine fluid, provides an attractive food-source that encourages ants and voles to visit and collect the seeds, helping to effect their dispersal (Ridley 1930; Molau 1993). The role of ants must not be exaggerated, however, as in a northern Netherlands study, seeds were not moved more than a few tens of cm, or not at all – small ants merely sucked on the elaiosome and presumably on the extra-floral nectaries too. The small distances the seeds were transported was thought to be due to the ants being hindered by the vegetation density and probably also because the elaiosomes soon lost their attraction by drying up (Masselink 1980).

In a study in the northern Netherlands, the mean number of seeds per flower ranged from 2.2 to 3.1. One plant may produce 40-50 flowers throughout the summer and therefore about 100-150 seeds. Counts revealed, however, that in most populations the number of seeds per plant was much lower, viz. 40-75 seeds, of which 20-60 may germinate, the others being viable but dormant. Hence the reproductive capacity is low. Many seeds fall victim to invertebrate and fungal attack and others are eaten by mice and other small animals. Normally only the most sheltered seeds survive predation after hibernation. Naturally, seeds in open sites will be more easily found by seed eating animals than those in sites with more dense grassy vegetation (Masselink 1980).

Germination takes place from late September until November (Masselink 1980).

Variation

Two subspecies, subsp. pratense and subsp. commutatum, are now recognised in Britain, but only subsp. pratense occurs in Ireland. Again, two varieties of subsp. pratense are distinguished on corolla colour, var. pratense and var. hians, the latter having the whole corolla a deep golden yellow (Smith 1963; Rich & Jermy 1998). In Fermanagh, the species has not been examined in sufficient detail to comment on these forms. As straightforward M. pratense, the species has been recorded in every Irish VC except Meath (H22) (Cen Cat Fl Ir 2).

Fermanagh occurrence

M. pratense has been recorded in 74 Fermanagh tetrads (14%), 66 of which have post-1975 records. As the distribution map indicates, it is widely scattered in the N and W of the VC, but only rare or absent from considerable areas of the more intensively farmed east of the county.

British and Irish occurrence

While it is well distributed across the whole of B & I from south to north, although absent from the Channel Isles, M. pratense becomes scarce and local in E Anglia, the east Midlands, SE Scotland and South Central Ireland. From the lowlands it ascends to 960 m in S Kerry (H1). M. pratense has been in steady decline in both B & I since before the 1930s, but the decline has accelerated since then. This is due to a combination of habitat loss and changes in land use involving the felling of woods and weedy overgrowth caused by woodland management neglect (F.J. Rumsey, in: Preston et al. 2002). In N Scotland, M. pratense appears to be limited to areas of peatland that are too wet to burn, as heaths and bogs are managed by periodic firing to reinvigorate sub-shrub grazing.

European and world occurrence

It belongs to the Eurosiberian boreo-temperate phytogeographical element and is present in most of Europe except the south, where it is absent from most of the Mediterranean. It is also in W Asia, east to the Yenisei region in Russian Siberia (Clapham et al. 1987; Hultén & Fries 1986, Map 1670).

Toxicity

Cow-wheat, like other members of the Scrophulariaceae, does contain poisonous glycosides which could cause illness and death in the unlikely event of animals eating a large quantity of them (Cooper & Johnson 1998).

Names

The genus name appears in Theophrastus, referring to a plant growing among wheat, 'Melampyrum' means 'black wheat' ('melas'= black; 'pyros'= wheat), the seeds being considered to resemble black grains of wheat (Gilbert-Carter 1964). The Latin specific epithet 'pratense' means 'growing in meadows' (Gilbert-Carter 1964), which is not quite what we observe today, since the species is much more of a wood and heathland species. This objection also applies to the seed colour referred to in the meaning of the genus name, which is brown, not black. The current author concludes that both of this species' names refer to a black-seeded plant (almost certainly M. cristatum (Crested Cow-wheat)) that grew amongst and probably parasitized cereal grasses. The seeds of M. cristatum are black and those of M. arvense are brown but go black (Britton 1943; Butcher 1961).

Prior (1879) suggests the common name, 'Cow-wheat' derives from the seed resembling wheat, the 'cow' element indicating their worthless nature as human food.

Grieve (1931) recounts some curious medieval folk-lore which may relate to the prevalence of the species in cornfields on land recently cleared of wood, presumably using fire.

Threats

None.

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