Trifolium hybridum L., Alsike Clover
Account Summary
Introduction, neophyte, a very rare casual.
1901; Praeger, R.Ll.; Co Fermanagh.
Growth form and preferred habitats
Alsike Clover is a short-lived alien perennial with globular heads of white flowers that turn pink as they age from the bottom of the inflorescence upwards and then go brown as they fade. In other respects, T. hybridum, which is a full species – and is not a hybrid between White Clover (T. repens) and Red Clover (T. pratense) as Carl Linnaeus erroneously thought – resembles T. repens, but it has ± erect stems up to 60 cm that do not root at the nodes. In case you are wondering, the English common name 'Alsike Clover' refers to a small Swedish village where Linnaeus collected the plant he named.
For several centuries, certainly from the 18th century onwards, Alsike Clover was regularly included in clover-grass seed mixtures planted for forage. However, when it was realised that it was far less nutritionally valuable than T. pratense (Red Clover), its use rapidly declined from the 1930s onwards. T. hybridum is scarcely used nowadays in agriculture in B & I, probably only occurring in pastures and meadows as a seed impurity.
Ecologically, Alsike Clover resembles T. pratense (Red Clover) in many respects, but is somewhat more adaptable and better able to tolerate wet, acid, infertile conditions. It is also more resistant to diseases like Clover Rot and Stem Eelworm than is T. pratense; in grass-clover mixtures it is considered non-aggressive, although it produces lower yields than Red Clover (A. Smith, in: Spedding & Diekmahns 1972, p. 419). The established strategy of T. hybridum as measured by the index developed by (Grime 1979) is described as C-S-R, meaning that it demonstrates a balance of the characteristic behaviours of Competitor, Stress-tolerator and Ruderal forms of plant natural selection affecting growth, reproduction and survival (Grime et al. 1988, 2007).
In comparison with most other legumes, T. hybridum does poorly on dry, sandy or gravelly soils, but does very much better than most on heavy silt or clay where there is plenty of moisture. T. hybridum can also survive flooding that would kill most crops and has been known to survive for a year and make extensive growth in water-covered soil (Duke 1981).
Perhaps on account of these tolerant properties, planting of Alsike Clover in Britain and Ireland has revived considerably in the last few decades and it has become a frequent constituent of amenity grass-legume mixtures and wildflower seed mixtures that are widely used for reseeding open habitats, including on roadside banks or for reclaiming less-than-ideal land (Sinker et al. 1985; Reynolds 2002; Crawley 2005). The form used is the hollow-stemmed subsp. hybridum and much of the seed sown in the 20th century and at present is imported from Canada where the plant is still used as a crop (Chater 2010).
Variation
There are two subspecies recorded in B & I, of which subsp. hybridum is the much commoner cultivated from: it has hollow stems, grows erect, is sparingly branched and has the larger inflorescence, over 20 mm in diameter. The other rarer taxon is subsp. elegans (Savi) Asch. & Graebn., which in contrast has solid, decumbent, much branched stems and bears an inflorescence less than 20 mm in diameter (Sell & Murrell 2009).
Flowering reproduction
Since the species has no means of vegetative spread or reproduction, it relies entirely on seed production for its increase, dispersal and survival. T. hybridum flowers from June to September and the flowers, being self-incompatible, require cross-pollination by bees. The legume pods, 3-4 mm long, are ± included within the calyx and they contain 2-4 seeds of varying colour. The pods are indehiscent, eventually falling off the inflorescence head to land at the base of the plant.
Although the individual plant is usually considered casual, failing to generate established populations, any seed that it manages to produce is capable of long-term survival buried in the soil (Thompson et al. 1997). The life-span of the individual Alsike Clover plant, which possesses a short root-crown, is variously quoted as being between three and six years (A. Smith, in: Spedding & Diekmahns 1972, p. 419). In agricultural sowings, however, T. hybridum is generally treated either as a biennial legume (Duke 1981, p. 243), or as an annual. Persistence in any event requires repeated sowing (D.A. Pearman, in: Preston et al. 2002).
Fermanagh occurrence
There are only three records of T. hybridum in the Fermanagh Flora Database. Apart from Praeger's completely site-unspecific record above, the other two were made by Ian and David McNeill in the NE of the county. The record details are: Drumbrick Td, 2 km N of Ederny, 1985, I. McNeill; Glen Lodge, 3 km N of Ederny, 1986, D. McNeill.
Irish occurrence
T. hybridum is still fairly widespread in Ireland, especially in the north on open road- and track-sides and on waste ground and it seems to be reduced to the status of an uncommon casual of such habitats, typically occurring as single plants or small patches (Cat Alien Pl Ir). However, it can also feature (again as a casual), in more damp or wet situations along other linear habitats, including beside rides and paths in conifer plantations and along river banks (Green 2008). In the late 19th and early 20th centuries, however, thanks to repeated agricultural sowings it was a frequent alien escapee in waste places in much of Ireland (Irish Topographical Botany). Occasionally it became established (particularly in the NE) and naturalised itself in open, dry, disturbed, wayside soils (FNEI 2; FNEI 3).
In the 1980s T. hybridum was much more often reported in the S & E of Ireland than elsewhere, while in the north at this period it became reduced to a rare casual, possibly of bird-seed and grain impurity origin, confined to open, sunny, ruderal habitats (FNEI 3).
The botanical survey of urban Belfast recorded it from 18 1-km squares in the city. It was most common in the central area of the city, nearest the docks, where grain and other imported seed was being transported in open-topped lorries (Beesley & Wilde 1997).
British occurrence
Frequent and widespread throughout lowland England and Wales, becoming more thinly scattered, scarce to rare further north, especially in N & W Scotland (New Atlas).
European and world occurrence
T. hybridum is regarded, possibly erroneously, as a native of N Europe, apparently simply on the grounds that Linnaeus (1745) mentions it in his Flora Suecica, as growing abundantly in the parish of Alsike, about ten English miles S of Upsala (Britten & Holland 1886). Whatever the site of origin, which is disputed, the species now occurs throughout Europe, reaching C Asia and Asia Minor. It has been introduced worldwide with agriculture, either deliberately or as a crop seed impurity (Duke 1981; Gillett 1985) so that now it is circumpolar (Hultén & Fries 1986, Map 1236).
Threats
None.