Centranthus ruber (L.) DC., Red Valerian

Account Summary

Growth form and preferred habitats

An established garden escape, native of rocky ground in Portugal and the Mediterranean basin, this colourful perennial has been present and grown in B & I gardens since around the latter half of the 16th century, when it was first mentioned by Gerard (1597) in his herbal. He mentioned it was growing in his garden, and that it was, "not common in England". This comment holds out the possibility that Red Valerian might at that point have been around in gardens for some period of time, and could perhaps already, on account of its wind-borne achenes, have escaped into the wild and have become part of our neophyte alien flora (Gwynn Ellis 1993). In England, it was first recorded beyond garden confines in Cambridgeshire in 1763 (P.J. Wilson, in: Preston et al. 2002).

C. ruber is a vigorous, rhizomatous, perennial with a branched rootstock that becomes rather large, thickened and woody after a few season's growth. This woody base, when rooted in lime mortar on old walls, can prove destructive by loosening stones or bricks. The plant produces numerous, erect, densely-arranged, glabrous, somewhat grey-green, hollow stems up to 80 cm tall, which branch rather feebly above. The stems have thickened nodes that bear thick-textured, fleshy, opposite leaves, up to 8 × 6 cm, that are both glaucous and glabrous, vary from ovate to lanceolate in shape and have mainly entire margins. The lower leaves narrow a little at their base to resemble a petiole, but the remainder of the leaves are completely sessile (Hutchinson 1972).

Individual flowers are very small, but they are extremely numerous and are borne in a terminal inflorescence described as, "an oblong panicle of cymes" (Hutchinson 1972).

After fruiting, in the autumn, the aerial branches die off gradually, although some usually survive and bear a few green leaves into late winter or early spring. The plant overwinters by means of a tuft of leafy, short green shoots up to around 15 cm tall on the woody base. These provide the growth points in the spring that develop into the summer flowering stems (Melderis & Bangerter 1955; Sell & Murrrell 2006).

In Britain and Ireland, C. ruber is more usually found in warmer, coastal or southern sites, on dry, disturbed or unstable, low-nutrient, calcareous habitats of high pH, such as maritime cliffs and shingle, other rocky and stony places, plus in more man-made environments, especially those in or near habitation, including mortar in stone and brick walls, in quarries and on waste ground, particularly in the latter two habitats if there is some degree of fly tipping from gardens (Perring & Walters 1962, 1976; Clement & Foster 1994; Stace & Crawley 2015).

The flowers vary in colour from the normal soft pink, to a stronger crimson or a warm white, occasionally cream. Locally, in Fermanagh, the flowers in the Brookeborough quarry are white, while those around Enniskillen town are the more typical shades of pink and red. The old, disused quarry is a place where people have a habit of fly tipping garden and other rubbish.

Genetic control of variation in flower colour

In a brief but absolutely fascinating conference address entitled 'The continuing evolution of weeds', Baker (1991), the elder statesman of weed ecology at the time, summarized the behaviour of weeds in general and gave detailed accounts of some significant examples found in California, including previously unpublished work on the colour forms of C. ruber. Baker described how the three colour forms or morphs differ fundamentally in their reproduction. The white form produces fewer inflorescences, each one with fewer flowers in comparison with the pink and red forms. The white flowers are ignored by the butterflies that visit and pollinate the coloured forms. In California, hummingbirds also ignore the white flowers and Baker says he has never seen moths on them either.

Baker interprets this pattern of flower form and potential pollinator behaviour as being the result of the white form being genetically dominant, capable of actively suppressing the gene for anthocyanin pigmentation. Thus gene A produces white flowers and is dominant (epistatic) over gene B which codes for pink or red flowers. The red flower form is homozygous recessive for each allele.

Plants of C. ruber in California (as in B & I) escaped from cultivation after their garden introduction and the white-flowered form has been found to be intrinsically less productive of flowers in a mixed population of the three colour forms. The white flowers produce fewer and lighter achenes, and Baker notes that the plants with white flowers may also be less drought tolerant than the other two colour morphs.

Local populations arising from one or just a few seeds may consist of only pink or red flowered forms, with no white despite the genetic dominance of the gene for white. White plants arise only from a white parent, so if these are absent, there will be no expression of the white gene, unless there is an appropriate mutation from within the coloured population. Thus as the weedy population beyond the garden wall develops and ages, there will be a progressive loss of the white flowered form, which will only be maintained if gardeners continually reproduce it in cultivation (Baker 1991).

Flowering reproduction

The main flowering period is from June to August, but at least on the Co Down coast (H38), flowering stretches almost to Christmas. The inflorescence contains a very large number of small, slender flowers borne in a number of terminal and side branch compound cymes that resemble a broadly cylindrical panicle. Like Valeriana officinalis (Common Valerian), the small individual flowers of Red Valerian are bisexual, irregular (ie zygomorphic) and have an insignificant-looking calyx on top of the inferior ovary that appears early on when the flower opens as a ring- or disk-like ribbed structure but consists of numerous linear segments inrolled at flowering, but which later, after the flower ovules are fertilised, unfurl and behave as described below (Webb et al. 1988). The slender corolla tube, 7-11 mm long, has an even more slender nectar spur, 4-8 mm long, attached at its base. The corolla mouth has five lobes, one larger and separate from the other four encloses the latter when the blossom is still in bud (Hutchinson 1972; Hickey & King 1981).

The flower has a solitary stamen and a style with a tiny, button-like stigma, both of which organs are exerted, eventually sticking out well beyond the corolla lobes. The long, slender corolla tube is also unusual in being longitudinally divided into two by a thin septum wall along its length, with the style and stamen positioned together on one side of the divide. The other side of the septum is perfectly clear and unobstructed, and it is down this long extremely slender portion of the corolla tube, lined by downwardly directed hairs, that the insect visitors (Hymenoptera and Lepidoptera, ie bees, butterflies and moths), attracted to the flower by colour and scent, stretch their proboscis or tongue to lap up the nectar that has been secreted into the spur (Hickey & King 1981).

Stace & Crawley 2015) remark that, "Red Valerian is a very good butterfly flower, especially attractive to Brimstones (Gonepteryx rhamni) in late summer, and it is also especially favoured by day-flying immigrant Hummingbird Hawkmoth (Macroglossum stellatarum).".

The flowers are strongly protandrous, the single stamen, inserted near the mouth of the corolla tube on a filament only 3 mm long, at first sticking straight out of the mouth of the corolla. However, after the solitary purple or yellow anther has dehisced, the filament that carries it becomes deflexed (bent down) away from the style, which then elongates to about 12 mm and takes its place at the mouth of the corolla tube, its obscurely bi-lobed stigma now receptive and awaiting an insect carrying the appropriate pollen from another flower or inflorescence. Automatic self-pollination is thus neatly and effectively avoided (Hickey & King 1981; Sell & Murell 2006).

The single-seeded dry fruit (achene or nutlet), 3.5 × 1.5 mm, that each fertilised individual flower ovum produces is crowned with a ring of beautiful, branched, plumed, white hairs, about 4.5 mm long, formed by the unfurled calyx. This plumose pappus acts as a parachute, enabling efficient wind dispersal of the attached brown, narrowly ovoid achene (Sell & Murrell 2006). Having said this, there often are huge numbers of seedlings produced at the base of walls on which Red Valerian is growing. There no estimates of seed longevity in the published soil seed banks of NW Europe (Thompson et al. 1997).

Fermanagh occurrence

There are eleven records from eight sites in separate tetrads in land-locked Fermanagh, all of them post-1980 in date. Three of the sites are fairly remote from habitation. The sites are widely scattered across the VC on calcareous lakeshores, river banks, old walls and in quarries. Their existence suggests this species is still spreading slowly in Ireland since it first escaped from garden cultivation around a century or more ago.

The details of the other seven sites are: Enniskillen town, from below West Bridge to the mouth of the Sillees River, July 1987, RHN; Brookeborough Quarry, 8 August 1995, RHN, still there June 2009; waste ground on N bank of River Erne at Belleek, 8 August 1990, RHN & RSF; Irvinestown, 2002, I. McNeill; Rosskit Island, Lough Melvin, 14 June 2003, RHN & HJN; Lisgoole, River Erne near Enniskillen, 30 May 2004, RHN; and grounds of Carlton Hotel, Erne Bridge, Belleek, 12 July 2006, RHN.

British and Irish occurrence

In NI, it is quite common along the Co Down (H38) and Co Antrim (H39) coasts (eg at Strangford Village and surrounds), but is much more rarely found at inland sites (Flora of Lough Neagh; FNEI 3; Urban Flora of Belfast).

In open situations, in dry or well-drained limestone terrain and, most particularly, in the bare karst landscape of the Burren, Co Clare (H09), C. ruber can invade, naturalise and occupy swathes of hillside, to the extent that when in flower it can be seen from a considerable distance. In the case of the Burren, Red Valerian was not imagined to be a problem species when Webb & Scannell published their Flora of the region in 1983, but the plant has spread and increased dramatically since that time, to the extent that it has become something of a threat to native limestone vegetation. While it certainly is easy to exaggerate the threat from neophyte invaders, C. ruber is so widespread and abundant in a few areas of the Burren, it may be very difficult to bring it under control without loss of indigenous flora, due to the mobility of its lightweight, air-borne seed. As Jarvis (2011) points out, "There was no visible boundary that might check the spread of this species, and, knowing it will grow on any garden wall, makes it hard to imagine how it might be eradicated.".

The New Atlas hectad map shows C. ruber is much more frequent and widespread in the southern half of Britain (including the Channel Isles), becoming very much rarer and mostly confined to the coast further north. It is absent from almost all of the Scottish Isles, including Orkney, Shetland and the Outer Hebrides (VCs 111, 112 & 110). Careful consideration of the New Atlas map indicates a very considerable increase and spread of C. ruber into new inland sites, from both pre-existing inland sites and from its previous predominant coastal occurrence in B & I. It has become abundant and invasive on consolidated maritime shingle and, if it is not already, it probably will become of conservation concern in parts of East Anglia (Stace & Crawley 2015).

The increase that has taken place since the 1962 BSBI Atlas is particularly noticeable in Ireland, where Red Valerian has also spread around much of the N & W coasts to areas where 40 years ago it was rare or absent (P.J. Wilson, in: Preston et al. 2002).

European and world occurrence

C. ruber is a native of the Mediterranean region and of W Asia, but being hardy, stress-tolerant and easy to grow in the garden, it has been very widely cultivated as a garden ornamental worldwide in suitable temperate and Mediterranean-type climatic regions. As a result of this, and of garden escapes, it has become thoroughly naturalised in W Europe outside its native range, and likewise in N America, Australia (http://www.flora.sa.gov.au/cgibin/speciesfacts_display.cgi?form=speciesfacts&name=Centranthus_ruber, accessed 30 January 2023) and New Zealand (Webb et al. 1988). In S Africa, it has been listed as an unwanted, proscribed invasive species, with punishments for its further introduction and spread. It has also been listed as invasive in parts of California and Oregon (https://www.invasiveplantatlas.org/subject.html?sub=13957, accessed 30 January 2023).

Names

The genus name 'Centranthus', often incorrectly spelled 'Kentranthus' is from the Greek 'kentron' meaning 'spur' and 'anthos', 'a flower'. The Latin specific epithet 'ruber' means 'red' (Johnson & Smith 1946; Stearn 1992). Grigson (1955, 1987) lists and mentions no fewer than 39 very varied English common names for this very colourful garden plant which he describes as, "cheerful and blowsy". Although there are so many, varied names, for instance 'Bouncing Bess', 'Drunken Willy', 'Fox's Brush', 'Good Neighbours', 'Lady's Needlework' and 'Sweet Mary', there are no explanations as to how the names arose in different parts of B & I. Grigson does not mention a widely applied name 'Spur Valerian' which previously was in common use, and which obviously is derived from the Latinised scientific binomial name.

Vickery (2019) records 50 English common names, and for some of them he does offer explanation. Vickery also suggests that the large number of local common names for C. ruber might have been on account of the plant spreading quite rapidly, its name did not and people therefore invented their own names for it. One name Vickery lists is 'Bovisand Soldier', "the plant being very abundant in Bovisand, in Devon". The 'soldier' connection is quite obviously the red colour, similar to British army scarlet uniforms of the 18th century and older. Other names listed by Vickery also mention the flower colour and soldiers, eg 'Scarlet Lightening' and 'Soldier Boys'. Six of Vickery's list of names include the word element 'drunken' such as 'Drunkards', 'Drunken Sailor', 'Drunken Willy' and 'Drunkits', said to derive from the way the flower-heads sway about in the wind. Many other names do not appear to have any obvious connection with the plant.

Uses

C. ruber does not share any of the herbal medicinal virtues or reputation of its relative Valeriana officinalis (Common Valerian), its main use being as a garden ornamental herb, although it is sometimes considered woody enough to be regarded as a garden shrub, at least in some countries. Grigson (1955, 1987) reports that very young leaves of Red Valerian are eaten in France and Italy in salads and are, "not at all unpleasant" if they are mixed in with other salad leaves. The leaves can also be treated like spinach, boiled, drained and mixed with butter, although Grigson says boiling does not destroy the bitterness of their taste altogether.

Threats

None.

References

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