Pedicularis sylvatica L., Lousewort

Account Summary

Growth form and preferred habitats

This is a low-growing (almost dwarf), monocarpic perennial with a thick, fleshy taproot and stems reaching a height of only 25 cm or less. It is a very variable plant and dwarf forms, only 6-7 mm tall, have been reported (Blamey & Grey-Wilson (1989). As the technical term indicates, monocarpic perennials fruit only once and they may take two or more years to develop sufficient energy reserves to allow them to trigger flowering behaviour (Grime et al. 1988, 2007). Lousewort produces several ± prostrate, decumbent stems 7-20 cm long and the erect or ascending flowering stem bears mostly alternate leaves 15-20 mm in length, fern-like, deeply divided pinnately and with small, toothed or pinnately lobed segments (Parnell & Curtis 2012). Like other members of the family, it is a hemi-parasite on the roots of its neighbours, principally grasses, but doubtless occasionally on the common nitrogen-fixing legume Lotus corniculatus (Common Bird's-foot-trefoil), with which it frequently associates.

Flowers of P. sylvatica can be easily separated from those of the more scarce or rare P. palustris (Marsh Lousewort) by having only one tooth on each margin of the upper lip of the corolla near the tip of the hood, as compared to the two teeth of the latter.

P. palustris is an abundant and virtually constant species of heathland, moorland and the better drained parts of acidic soils and peat (including that developed directly over limestone rocks). As such, it very regularly frequents blanket bog and heathy upland pastures, marshy lakeshores and the drier parts of raised or valley bogs. It is found at all altitudes, although predominantly in the uplands where it reaches 915 m. Essentially a species of fairly wet acid soils, including flushes, it can, however, tolerate some degree of summer drought (Sinker et al. 1985). In Fermanagh, with a close proximity to the Atlantic Ocean from where most weather arrives, Lousewort is rarely much tested with respect to drought conditions!

The established strategy of P. sylvatica is categorised as SR, meaning it is a Stress-tolerant Ruderal species (Grime et al. 1988, 2007).

Flowering reproduction

P. sylvatica flowers from April to July or August and is mainly pollinated by bumble-bees (Garrard & Streeter 1983). The pollination mechanism is the same as that for P. palustris described in detail in the current author's (RSF's) species account on this website. The flowers, 15-30 mm long, are bright pink or red (rarely white) and 3-10 of them are borne in a short, loose (or lax), terminal spike-like cluster. The calyx is bright green, tubular, angular, inflated when the flower is in fruit, hairless, dividing above into five fimbriate, leafy lobes (ie it is not 2-lipped) (Butcher 1961; Clapham et al. 1987). The corolla tube exceeds the calyx in length and it is 2-lipped: the upper hooded lip and lower lip are of about equal length. As with the taller and more floriferous P. palustris, the flowers produce copious nectar for their size and children, at least in past times, made a habit of sucking the flowers to drink their honey, giving rise to numerous related English common names for the two 'Louseworts' or 'Red Rattles'.

The fruit is a two-valved capsule, 12-15 mm, ovoid, shortly acuminate at apex, shorter than or equal to the calyx tube (Sell & Murrell 2007). The capsule contains a few angular seeds, each 3.0 × 1.6 mm, ovoid, netted, finely striate, brown (Butcher 1961; Melderis & Bangerter 1955).

The seeds are said to possess an elaiosome food body that is designed to attract ants which should help in seed dispersal. The oil-containing food body is unusual in this instance because in P. palustris it is derived from a protruding endosperm-haustorium (Berg 1954). The haustorium is the organ with which the roots of the hemi-parasite species attach to the roots of their host plant(s), and this is a very unusual modification in this species. The seeds are also reported to be usually partially winged (Stace 2019) and, unlike those of P. palustris, seeds of P. sylvatica are transient in the soil seed bank, persisting for less than one year (Thompson et al. 1997). The current author (RSF) has not been able to gather information on the level of seed production for this species from the literature available to him, nor any study of its seed dispersal.

The seeds rattle inside the capsule when the fruit is ripe, giving rise to one of the English common names.

Fermanagh occurrence

P. sylvatica has been recorded in 196 Fermanagh tetrads, 37.1% of those in the VC. It is common and widespread, especially in the more upland western half of the county.

Variation

Two subspecies are recognised in B & I, subsp. sylvatica with a hairless calyx, which is the most common form in Fermanagh, and an endemic Irish variant with a hairy calyx referred to as subsp. hibernica, which so far has only been recorded at four sites in Fermanagh and is doubtless regularly overlooked (Revised Typescript Flora; An Irish Flora 1996). A third subspecies, subsp. lusitanica (Hoffmanns. & Link) Coutinho, is described in Flora Europaea 3 and is endemic to Portugal and SW Spain (E. Mayer, in: Tutin et al. 1972).

British and Irish occurrence

Frequent throughout the whole of B & I in damp heathy places, except for parts of the English Midlands where it is scarce and local. There has been a widespread decline in S & E England due to the loss of heathland and unimproved grassland habitats. Analysis of BSBI databases indicates that most of these losses have taken place since 1950 (F.J. Rumsey, in: Preston et al. 2002).

European and world occurrence

P. sylvatica belongs to the European temperate phytogeographical element and is widespread in W & C Europe, having its greatest frequency in W Europe. It is, however, completely absent from S Europe and the entire Mediterranean region. It extends northwards to C Sweden and eastwards to Lithuania and W Russia (Clapham et al. 1987). Subsp. sylvatica is distributed through the range of the species, except Portugal. Subsp. hibernica occurs across NW Europe, from Ireland to Norway. P. sylvatica has been recorded in SE Newfoundland, but it is not considered native in N America (Hultén & Fries 1986, Map 1697).

Uses

Previously P. sylvatica and Rhinanthus minor (Yellow-rattle), being closely allied to the Euphrasia spp., Eyebrights, were used in herbal medicine, but as remedies they have now fallen into disuse. Old herbalists such as Culpepper considered P. sylvatica, which they referred to as 'Dwarf Red Rattle', a wound herb and styptic (Grieve 1931). Culpepper (1653) says of 'Red Rattle', "accounted profitable to heal up fistulas and hollow ulcers, and to stay the flux of humours in them, as also the abundance of women's courses, or any other fluxes of blood, being boiled in red wine and drunk".

Names

The genus name, 'Pedicularis' is derived from the Latin 'pediculus', 'a louse' (Johnson & Smith 1946) and the species get their 'Lousewort' common name from the old belief (or myth) that, "it filleth sheep and other cattle, that feed in meadows where this groweth, full of lice" (Lyte 1578; Gerard 1597, 1633). Two of the other English common names are 'Dwarf-' or 'Lesser-Red Rattle' which refer to the ripe seed rattling inside the base of the dry capsule and, also, the colour of the flowers (Prior 1879; Grieve 1931). The Latin specific epithet 'sylvatica' is from 'silva' meaning 'woodland' and translates as 'growing in woods', which is completely incorrect, making it a misnomer (Gilbert-Carter 1964).

A total of eight additional English common names are listed by Grigson (1955, 1987), several of which refer to the practice of children sucking the nectar from the flowers, eg 'Bee-sookies', 'Honey sookies', 'Honeysuckle' and 'Sookies'. The other names refer to the rattle of seeds in the ripe capsule, eg 'Rattle baskets', 'Rattle pods' and 'Shackle-boxes'.

Threats

Common and widespread and not under threat.

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