Wormwoods, Mugworts & Ragweeds
What are they?
This is a group of plants in the daisy family (Asteraceae), although the rather small and underwhelming flowers may not make this immediately apparent. However, a closer inspection of a 'flower' will reveal that it consists of a tight collection of tiny florets, surounded by an outer layer of small, overlapping bracts. Thus, the flowers are very like those of daisies, but without the outer ring of showy petals. There are two main groups here; the wormwoods in the genus Artemisia are mostly herbaceous perennials which often spread over time to form spreading clumps, typically with the woodt remnants of previous years' growth at the base. The ragweeds in the genus Ambrosia are annuals and, though they may get tall by the end of the year, typically die down after setting seed and do not regenerate. Thus, the latter tend to be single-stemmed and not spreading, though individual plants can be quite bushy looking.
Where are they found?
Wormwoods are mostly highly aromatic plants, often with silvery foliage, which has made them popular as garden ornamentals. Most are persistent perennials so such plants are most likely to be found as survivors from dumped garden waste on roadsides and waste ground. We also have three native species with Common Ragwort being abundant in all kinds of grassy places while Sea Wormwood occurs in saltmarsh. The ragweeds are rather scarce and most often turn up where they have germinated from spilt birdseed.
Identification
Members of this group are easily recognisable by their branching heads of many, petalless flowers which appear generally in late summer and held well above the foliage. With the flowers all being rather similar, identification to species mostly rests on details of the hairs (with several species being thickly clothed in white hairs so as to appear silvery from a distance) and the shape of the leaves.
Common Mugwort Artemisia vulgaris
Probably an ancient introduction, now well established. An abundant species that grows in all kinds of grassy places, especially roadsides and field edges. Flowers July to September. A very variable species in the shape of its leaves, which tend to have broader lobes on basal, early-season leaves and narrow, fingered lobes on upper leaves. The leaves are green above and contrastingly whitish below with a strong but not unpleasant aroma. An aggressive perennial that can spread to form large colonies of dense stems, to 150cm in height.
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Chinese Mugwort Artemisia verlotiorum
A rare introduction from Asia, recorded a handful of times in East Anglia but which may become more common in the future. Flowers October to November. Rather similar to Common Mugwort but forms a more open, less upright plant, the deeper green leaves being more finely cut and continuing as leafy bracts well into the flowerhead.
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Common Wormwood Artemisia absinthium
An ancient introduction as a herbal remedy that is uncommon but persists in a few grassy places on roadsides and commons. Flowers July to August. A Silvery-grey species with neatly dissected leaves. Plants may be upright or more open and semi-prostrate in habit.
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Sea Wormwood Artemisia maritimum
A native species of saltmarshes where it can be locally common on slightly drier ground along natural levees beside creeks. More recently starting to appear as a plant of salted roadsides. Flowers August to September. Leaves aromatic and deeply cut almost to the veins into very narrow lobes.
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Field Wormwood Artemisia campestris
A very rare native which in the UK is found only in Breckland. Although once more widespread in very dry, Breckland heaths, this plant is now considered native at just three sites, though it has been recently introduced to a few more, protected sites. Flowers August to September. A graceful species to 75cm in height, usually forming a many-branched clump. Leaves silvery green, very finely cut into linear segments.
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Annual Mugwort Artemisia annua
A rare introduction from eastern Europe and central Asia, recorded in Cambridgeshire. Flowers August to September. Unusual in this group in being an annual, which can be deduced by the lack of old, woody stems bases. Leaves bright green, richly aromatic and in appearance rather like those of Feverfew.
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Western Mugwort Artemisia ludoviciana
Introduced from North America as a garden ornamental, recorded in Cambridgeshire. Flowers July to August. A densely white-hairy plant with deeply toothed or simple leaves.
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Tarragon Artemisia dracunculus
Rare as a garden throw-out in waste places, twice recorded in our region. Flowers July to October. The whole plant has a strong, herby smell and typical wormwood flowers, but differs from other species in its simple leaves.
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Common Ragweed Ambrosia artemisiifolia
Introduced from North America and appearing only rarely as an arable weed or where seed for birds has been spilt. Flowers August to October. An annual which may grow to a metre in height but often much less.
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Great Ragweed Ambrosia trifida
Introduced from North America and appearing only rarely as an arable weed or where seed for birds has been spilt. Flowers August to October. An annual capable of growing to three metres in height but as a birdseed alien, it often only achieves a metre at the most. Leaves mostly three- to five-lobed, with the uppermost unlobed.
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Giant Sumpweed Cyclachaena xanthiifolia
(Marsh Elder) Introduced from North America and formerly recorded near dockland sites in Suffolk. Flowers July to September. An annual capable of growing to two metres in height. Leaves deeply toothed at the margins and typically simple, but sometimes three- to five-lobed. The whole plant has a grey-green coloration and the leaves have a rough, sandpapery texture which distinguishes non-flowering plants from the otherwise rather similar goosefoots.
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