Chrysanthemum segetum L., Corn Marigold

Account Summary

Growth form and preferred habitats

A handsome, brightly colourful, yellow-headed, hairless, somewhat glaucous (ie bluish-green), erect or straggling annual of much-branching habit, C. segetum used to be a locally common, naturalised weed of arable crops. Growing from a taproot and well-developed fibrous root system, it produces a furrowed, leafy stem, simple or branched, usually around 20-60 cm tall. Leaves are alternate, all but the basal ones stalkless and clasping the stem, 2-10 cm, oblong-lanceolate in shape, but irregularly lobed or coarsely toothed, aromatic and fleshy (Melderis & Bangerter 1955). The upper leaves on plants are often entire and plants with only ± entire leaves do also occur quite frequently (Howarth & Williams 1972).

Corn Marigold is a lowland plant of acidic arable fields (both root crops and cereals) and ruderal wasteground in B & I, occurring up to 240-335 m at most. It is also found as a casual weed species around field gateways, along roadsides and on field margins usually in open, disturbed, fertile soils, particularly nitrogen-enriched ones. It is absent in the wild from calcareous soils. C. segetum is most frequent on light sandy or loamy acidic soils and is regarded as an indicator of calcium-deficient cultivated soils, so that in the past liming was widely used to check its occurrence. It withstands drought very well on account of its extensive root system, but vegetative plants cannot survive any degree of frost (Howarth & Williams 1972).

Since the 1980s, it is frequently included in so-called 'wild flower seed mixtures', widely sown both by 'Green' gardeners and local councils in urban areas of B & I.

Flowering reproduction

The plant is tolerant of grazing by cattle, horses and fowl, branching vigorously in response to this herbivory. The seed can survive passage through animal guts and are dispersed in their dung. The seeds germinate from March to May and the plants have their main flowering period between June and August, with a small-scale secondary late flowering from September to October. Terminal flowerheads, 3-7 cm in diameter, are produced on long, leafy, hollow peduncles that enlarge upwards. The flowerheads are ± flat and have numerous bright-yellow, spreading female ray-florets and paler, golden-yellow, central bisexual tubular flowers. The involucral bracts are broadly ovate, arranged in three or four rows, each one with wide membranous margins (Melderis & Bangerter 1955; Butcher 1961; Hutchinson 1972). There is a form of the plant that has no ray-florets, forma discoideum. Occasional plants with extra ray-florets, ie double forms, do also occur (forma plenum) (Howarth & Williams 1972).

Pollination is by insects, principally Coleoptera (beetles) and Lepidoptera (butterflies and moths), but also involving various Diptera and Hemiptera (Flies). About one quarter of the plant's photosynthetic resources are devoted to reproduction, a figure similar to that for another more common annual weed, Senecio vulgaris (Groundsel) (Howarth & Williams 1972; Harper & Ogden 1970).

C. segetum is moderately plastic in its response to growing conditions; in open situations with little competition it can grow up to 100 cm tall bearing many branches, such plants can each produce up to 3,000 achenes. The achenes are 1.5 mm long, strongly ribbed and are of two kinds: those of the ray-florets are compressed and have two lateral wings making them triangular in cross-section, while those produced by the tubular-florets are cylindrical and unwinged. Both types of achene lack a feathery pappus to assist their dispersal.

In dense stands and in unfavourable sites, plants may be unbranched and grow only about 10 cm tall, yet they may still manage to produce a flowerhead and yield around 200 achenes per plant. Salisbury (1964) estimated that under these stressful conditions the mean or average number of heads per plant is seven, each head producing 176 ± 10 achenes.

Seed dispersal is probably mainly associated with animal ingestion, although winged achenes produced by the ray-florets can float on water for up to two days and may disperse in this way. Seed can also be dispersed with mud, becoming attached externally to animals and machines. The current author (RSF) noted a solitary small plant that appeared in the gravel around his house, exactly where he habitually parks his car!

Achenes can survive dormant in soil for some years, but the maximum period is certainly less than 15 years (Howarth & Williams 1972).

Variation

In addition to the already mentioned variation in leaf shape and ray-floret number, several horticultural varieties occur, especially var. album, which is a pale-flowered form, var. pumilum (or cv. 'Little Gem'), which is a dwarf compact and free-flowering variation and var. grandiflorum, with larger flowerheads than normal. Two other cultivars are mentioned in the Royal Horticultural Society's Index of garden plants, 'Eastern Star', which has flowerheads of primrose yellow with a brown disc and 'Evening Star', which has golden flowerheads (Griffiths 1994).

Status and origin

Earliest records of this colourful annual weed in various parts of the British Isles are associated with archaeological sites, in Scotland going back to the Neolithic period and in Dublin to mediaeval times. It is now generally accepted that C. segetum is an introduction associated with early agriculture, ie it is an archaeophyte (Howard & Williams 1972; Godwin 1975; Ellis 1993; Stace 1997). On the other hand, it could also be argued that C. segetum and other previously more familiar arable weeds of corn and potato fields may be natives which could have thrived on the vast expanses of nutrient-poor debris and skeletal boulder clay soils left after the periodic retreat of the glaciers 10,000-12,000 years ago (Godwin 1975; Wilson 1992). These ruderals might thus have persisted in open and disturbed situations (many of them perhaps at the coast), until the introduction of arable farming to Ireland at some time during the Neolithic period around 5,700 years ago (Mitchell 1986). We may never have a definitive answer to the question if this is the case or not.

Changes in agricultural practices over the last 50-70 years, including the huge local decline in arable agriculture, efficient seed cleaning, the introduction of new crop varieties (especially winter-sown ones) and the very extensive use of agro-chemicals, including both fertilisers and herbicides, have forced C. segetum and other arable weeds to occupy marginal and more or less disturbed habitats. The result of such landuse changes has been a greatly reduced occurrence of these once common weeds throughout B & I and, indeed, throughout Europe (Howarth & Williams 1972; Andreasen et al. 1996, Rich & Woodruff 1996).

Fermanagh occurrence

Arable agriculture has declined in Fermanagh to such an extent in the post-war period that C. segetum now only occurs very occasionally on disturbed top-soil after germination of long-dormant seed. It has been recorded in a total of 20 thinly scattered Fermanagh tetrads, although only 14 of these have post-1975 records.

British and Irish occurrence

C. segetum has an Atlantic-Mediterranean or Atlantic-subatlantic distribution, and although it may still appear locally frequent, as it does in parts of N & E Ireland, it has steadily declined for many years due to measures that include improved seed cleaning, herbicide spraying and the move to autumn-sown crops. We have now arrived at the stage where species like this one, that previously were an economic threat, have become a conservation priority, or this possibility is at least a live issue. The BSBI Atlas 2020 hectad map shows that C. segetum remains widespread throughout lowland B & I at that level of discrimination, but it is frequently recorded from ground sown with wild flower seed mixtures and is really only locally frequent and occasionally abundant in light sandy soils near coasts (H.J. Killick & P.A. Stroh, in: Stroh et al. 2023).

European and world occurrence

C. segetum probably originated in the E Mediterranean region, Asia Minor and W Asia, but has spread with arable agriculture, and is, or previously was, well established throughout Europe as far north as 70^oN in Norway, although in more northern areas it has always been regarded as a casual species. It has also been introduced in N & S America, N & S Africa, Australia and New Zealand (Howarth & Williams 1972; Hultén & Fries 1986, Map 1814; Clapham et al. 1987).

Names

The genus name 'Chrysanthemum' is a name dating back to Dioscorides and is a combination of two Greek words, 'chrysos', 'gold' and 'anthemon', 'flower' (Johnson & Smith 1946). The Latin specific epithet 'segetum' means 'of cornfields' (Gilbert-Carter 1964). There are a total of 41 English common names for C. segetum provided from around B & I by Grigson (1955, 1987), many of them referring to the beautiful golden yellow flower colour. The 'gold' word element is also widely reflected in Anglo-Saxon placenames such as 'Goldhanger' in Essex and 'Golding' in Shropshire (Grigson 1955, 1987). Vickery (2019) lists a total of 69 English common names, proving just how well this plant was known across these islands in past times when it was a real nuisance weed of arable agriculture.

Threats

Conservation of plants of disturbed sites has only recently been raised as an issue and it may be difficult for statutory bodies to gain powers and to balance environmental priorities. Weed conservation requires a major shift in thinking, which will also necessitate a major educational effort to convince the inevitable sceptics.

References

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