Gnaphalium sylvaticum L., Heath Cudweed

Account Summary

Growth form and preferred habitats

G. sylvaticum is a visually unimpressive, erect or ascending, unbranched, greyish-hairy, calcifuge, rosette-forming, wintergreen perennial arising from a short woody stock. Basal leaves are long and narrow, entire, green above and covered with woolly white hairs (tomentum) below (Hutchinson 1972). Flowering stems are usually less than 30 cm tall but can be twice that height. They are leafy to the top and bear small, tubular to egg-shaped, dark, brownish-black tipped flowerheads, which can either be solitary or held in clusters of two-eight, the whole inflorescence often forming a long, loose, narrow spike, that is usually around half the length of the flowering stem, although it can be short and congested in a form called var. alpestre Brügger (Huxley 1967; Sell & Murrell 2006). It is readily identified from related species by the fact that the leaves are alternate, definitely one-veined, the lower stem leaves stalked, lanceolate and pointed, and they become gradually more narrow, shorter and stalkless (sessile) further up the stem (P. Stroh, in: Stroh et al. 2019). All leaves are ± hairless above and woolly white beneath.

The species it is most likely to be confused with is G. norvegicum (Highland Cudweed), but it is a rare species confined to a few sites in Scotland.

G. sylvaticum is a species of open, generally lowland communities on dry, acidic, bare or thinly-vegetated heathy, moorland and woodland trackside habitats, on infertile, sandy, gravelly or peaty soils, including in old gravel-quarries, sand-pits and on coastal dunes. Such disturbed habitats are often only intermittently available and they need to be either fully-lit or in light-shade only. G. sylvaticum has also been recorded on heavy wet clay soil in Cumbria (Halliday 1997), which appears an unusual substrate for the species.

As indicated by both its scientific name and one of its alternative English common names, 'Wood Cudweed', G. sylvaticum has connections with woodlands, often frequenting open woods, along tracks or roadways in woods, or appearing in woodland clearings or after trees have been felled, including for coppice and in scrub (Garrard & Streeter 1983). It is possible that fires after woods have been cleared or coppice cut, may help provide requisite conditions for colonisation by dormant seeds in the soil (Salisbury 1942).

Populations reported in both B & I in recent years (2008-2013) are small, often comprising less than 20 individuals and they all appear to be declining towards local extinction (Walker et al. 2017). The established strategy of G. sylvaticum is categorised as SR/CSR, meaning it is intermediate between a Stress-tolerant Ruderal and a more balanced mix of all three plant strategies, Competitor, Stress-tolerator and Ruderal (Grime et al. 1988, 2007).

Although it is mainly found in lowland settings in B & I, Heath Cudweed reaches an altitude of 950 m near Inverness (VC 96), and in continental Europe it reaches 2,500 m in the Pyrenees, Alps and Apennines (Huxley 1967).

Flowering reproduction

G. sylvaticum is regarded as a short-lived perennial that relies entirely on its seed production to survive. Being decidedly inconspicuous, the plant is best looked for when it is flowering, which takes place from July to September. The flowerheads are small, 6-7 mm in diameter, and are arranged, almost sessile, amongst slender leaves along much of the upper half of the erect flowering stem. The entirely tubular flowers likewise are very small and insignificant-looking, apparently attracting very few insect visitors. The outer flowers in each flowerhead are female and threadlike, and comparatively few of the tubular innermost ones are bisexual (Sell & Murrrell 2006). Thus the flowerheads are probably either wind-pollinated, or the plants being rare, isolated and often present only in small populations, individuals may self-pollinate, since in every situation they must set seed in order to survive. Very probably for this reason, populations are also known to vary considerably in numbers from year to year (L. Farrell, in: Stewart et al. 1994; P. Stroh, in: Stroh et al. 2019)). To some extent this is probably governed by the necessity for a measure of regular, at least annual disturbance, bringing buried seed to the surface, enabling germination. The species has a reputation of reappearing in old sites where it has not been seen for some time, when they are cleared and the soil surface disturbed, it may re-emerge after about two years or so, eg in Monkwood, Hampshire (Brewis et al. 1996).

The achene fruits are 1.5 mm long, cylindrical and textured with papillae and short, stiff hairs. The pappus hairs are sometimes described as 'barbellate' (Hutchinson 1972). The attached pappus is 3.5 mm long, reddish in colour and composed of a single row of simple hairs. Despite being wind-dispersed, distance travelled by most seed is likely to be very short due to the usually low height of release from the plant.

Flower production statistics are provided by Salisbury (1942), who must have been able to work with much bigger populations of better grown plants than most of us encounter today. The number of fruiting flowerheads or capitula from 41 sample plants he describes ranged from 23 to 571 per plant, giving a total of 5,465 and an average of 132.3 ± 11.4 per plant. A mean figure for the number of achene fruits per flowerhead was calculated from a sample of 36, and was an average of 68. Thus the calculated mean seed output was 9,042 ± 991, or approximately between 8,050 and 10,000 achenes per plant per annum.

Seed of G. sylvaticum has the reputation of being long-lived and the survey of soil seed banks in NW Europe contains just three estimates, two of which regard it as short-term persistent, ie, seed surviving more than one year but less than five. The third study recognised that there was seed in the soil, but could not allocate the survivability to any of the three categories involved, so it was indeterminate (Thompson et al. 1997).

The genus is one with so-called 'everlasting flowers' since the stiff, dry scales of the involucral bracts remain on the plant long after the flower is dead and the achenes have been dispersed (Melderis & Bangerter 1955).

British and Irish occurrence

As the hectad maps in both the New Atlas and the Atlas 2020 prove, the distribution of Heath Cudweed was once frequent and widespread throughout B & I. However, despite the relatively wide range of possible habitats open to this species, both inland and coastal, it declined surprisingly quickly from being widespread and locally abundant in the 1950s, to distinctly local, isolated and of increasing rarity. The intensification of agriculture and especially the widespread and frequent use of artificial fertilisers has led to nutrient enrichment of the whole environment, which has encouraged the growth of taller, more aggressive, shading plant species including Pteridium aquilinum (Bracken) and Urtica dioica (Stinging Nettle), to name just two vigorous invasive species that very easily outcompete and quickly and permanently oust the likes of G. sylvaticum. In addition, it is very susceptible to commonly applied herbicides, and this too must have gradually depleted the soil seed bank persistence (which is not like Papaver rhoeas (Corn Poppy), but merely of short-term duration), and thus it is rather quickly and efficiently exterminated from many local populations over the past 60 years of BSBI survey monitoring (Walker et al. 2017).

Over the last 60 years, G. sylvaticum has declined to reach a remarkable degree of rarity in both islands, becoming labelled 'endangered' for conservation reasons. This is especially the case in Ireland, where population fragmentation and subsequent isolation has resulted in major losses in the Republic of Ireland, so that most of the remaining Irish sites are situated in the northern counties of Ulster (Rich & Woodruff 1990; L. Farrell, in: Stewart et al. 1994; An Irish Flora 1996; Forbes 2007). In Co Tyrone (H36), McNeill (2010) described G. sylvaticum presence as, "rather rare". Twelve post-1980 records were then listed in Tyrone, most of them by Ian McNeill. In the RoI, seven populations, varying in size from five to 35 plants (hiding under the revised name Omalotheca sylvatica (L.) Sch. Bip. & F'W. Schultz), were managing to persist in Co Wexford (H12) until 2019, when searches failed to find any plants (Green 2022).

The presence and distribution of G. sylvaticum in Britain has definitely been in decline since at least the 1950s, but in parts of south-central England it remains local and occasionally frequent in sites in Hampshire (VCs 11, 12) and Berkshire (VC 22) although, in truth, populations are still on the wane (Brewis et al. 1996; Crawley 2005). The main stronghold of Heath Cudweed in Britain remains in N & NE Scotland, but Walker et al. (2017) have reported significant declines happening even there, "with the species having been lost from more than half of all Scottish sites surveyed (16 of 27)". In the same vein, in Wales, Stroh et al. (2019) states that G. sylvaticum, "had post-1986 records from Caernarvonshire (VC 49), Denbighshire (VC 50), Merionethshire (VC 48) and Monmouthshire (VC 35), although it may now only persist in the latter two counties". It became extinct in Montgomeryshire (VC 47) after 1966, when a single plant was recorded (Trueman et al. 1995).

When a species like Heath Cudweed becomes scarce, it is low reproductive capacity rather than rates of mortality that prevents effective exploitation of suitable habitats on the increasingly rare occasions when these become available under modern conditions. In woodlands where G. sylvaticum was refound in the Walker et al. (2017) five-year survey, the habitat was kept open by disturbances that included vehicle traffic or coppice rotation. On heaths and pastures, grazing by sheep kept the sward sufficiently short for Heath Cudweed to persist to some extent. However, in many known sites which had small populations, there was no conservation management plan in place, so that growing conditions were inevitably less than perfect for G. sylvaticum reproduction and survival (Walker et al. 2007).

Fermanagh occurrence

The situation in Fermanagh reflects this major decline in the species, with just two recent observations recorded, in each instance only a solitary plant being found. G. sylvaticum has been recorded a total of just seven times in Co Fermanagh, occurring in widely scattered sites on damp sand on lakeshores, river banks and in a sand pit. The additional record details are: sandy pastures, Shanco Td, near Lough Eyes, July 1949, MCM & D; on sandy ground by the Kesh River near Water Foot, 1951, MCM & D; abundant in pasture by Many Burns River, N of Many Burns Bridge, 1953, MCM & D; lane west of Spectacle Lough, 1953, MCM & D; Lough Lea, Knocks Td, ENE of Lisnaskea, 10 October 1987, RHN; sand pit at Pubble Bridge, Tempo River, 20 August 1999, RHN & RSF.

British populations are described as varying greatly in numbers from year to year (L. Farrell, in: Stewart et al. 1994), but, as is clear from the above record details, there has been insufficient experience of the plant in Fermanagh to confirm or deny this effect locally.

The plant is described as regularly occurring along forestry tracks in Britain, growing in peaty sand and gravel (Stewart et al. 1994; Brewis et al. 1996; Halliday 1997), but in Fermanagh it has not yet been observed in this type of rather frequently occurring, disturbed habitat.

European and world occurrence

The world distribution of G. sylvaticum is categorised as 'Amphi-Atlantic', meaning it spans the ocean from Europe to N America. Its phytogeographic distribution is also listed as Eurosiberian boreo-temperate, in Europe stretching across most of the continent from NE Spain to N Norway, although it is much less prevalent towards the south and, indeed, it is absent from all the Mediterranean islands. G. sylvaticum is also well represented in adjacent parts of W & C Asia, from the Caucasus and Iran to Siberia. It is also considered native in eastern N America (where populations are also in decline) and has been introduced into New Zealand (Hultén & Fries 1986, Map 1787; P. Stroh, in: Stroh et al. 2019).

Names

The genus name 'Gnaphalium' is from the Greek 'gnaphalion' meaning 'wooly' or 'soft down' and is an obvious reference to the felted leaves of the plant (Johnson & Smith 1946; Gilbert-Carter 1964; Gledhill 1985). The Latin specific epithet 'sylvaticum' is from 'silva', 'woodland' and means 'growing in woods' (Gilbert-Carter 1964).

Threats

Changing agricultural practices, and especially the decline of arable agriculture in Ireland, the move to winter-sown crops and the use of herbicides and agrochemicals have together depleted the soil-borne seed bank of this species to near zero, forcing it towards smaller, more marginal, less regularly disturbed ground. In addition, fertilizer run-off and other forms of soil nutrient enrichment, for instance, nitrogen from car exhausts, encourages vigorous competitors to outgrow it, while herbicide drift kills off this species entirely.

References

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