Ambrosia artemisiifolia

Daisy & Dandelion Family [Asteraceae]

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Pappus: pappusZpossible (white)
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petalsZ0 petalsZ5

4th Sept 2012, Coalville, Leicestershire. Photo: © Chris Cafferkey
Not entirely dissimilar to Ribbed Melilot (Melilotus officinalis), but that has trefoil leaves and belongs to the Pea Family (Fabaceae). It grows to 1m.

4th Sept 2012, Coalville, Leicestershire. Photo: © Chris Cafferkey
At first the un-opened flower buds might be mistaken for seeds or fruits, since it flowers later in the season.

4th Sept 2012, Coalville, Leicestershire. Photo: © Chris Cafferkey
Flowers are in a spike, which at first has the flower buds clustered closely together.

4th Sept 2012, Coalville, Leicestershire. Photo: © Chris Cafferkey
 But as the flower spike grows the flowers get more spaced out. Unusually, the flowers are all clustered underneath a cap-shaped bract which acts like a mini umbrella. The flowers themselves consist of closely-packed disc florets, from which a yellow tubular skirt descends which perhaps five thin filaments are suspended. The stem has long yellowish un-straight hairs, as do the bracts. All the flowers here are male. The female flowers (not shown) are in the leaf axils and are not recognisable as flowers in the generally accepted parlance.

4th Sept 2012, Coalville, Leicestershire. Photo: © Chris Cafferkey
The leaves are bi-pinnate with blunt lobes similar to many Wormwoods and Mugworts which belong to the same Artemisia species.

Not to be semantically confused with : Common Ragwort (Senecio jacobaea) or Oxford Ragwort (Senecio squalidus) [a plant of similar name which is in the same Daisy & Dandelion Family (Asteraceae) which have similar, but not identical, leaves]

Some similarities to : Ribbed Melilot (Melilotus officinalis) (jiz) and to Vervain (Verbena officinalis), but mostly to Mugworts or Wormwoods such as Norwegian Mugwort (Artemesia norvegica) or Wormwood (Artemesia absinthium), Field Wormwood (Artemesia campestris) and Sea Wormwood (Artemesia maritimum) (both leaves and flowers).

Slight resemblance to : Monk's-hood (Aconitum napellus) (leaves only).

Ragweed has separate male and female flowers; the male flowers are much more prominent than the female ones which are tucked in the leaf axil, whereas the male flowers are clustered underneath a bract which acts as an umbrella.

Unusually, the flowers are held upside down within a cap-shaped bract. There are no ray florets, only disc florets, but unusually the disc florets have a yellow tubular skirt which hangs down, the skirt having five narrow yellow filaments dangling from the periphery. In some ways the stringy filaments might resemble Fringe Cups (Tellima grandiflora) which belongs to the Rose Family (Rosaceae), but there the filaments are multiply bifurcated. Norwegian Mugwort also has disc florets held upside down, but otherwise the two are quite dissimilar. Nodding Bur-Marigold is another with only disc florets held upside down, but in each case the florets are held within a cap consisting of many sepals, rather than the monocoque cap of Ragweed.

Ragweed differs from Perennial Ragweed where the flowers are held facing sideways rather than downwards. They too are held within sepals rather than a monocoque cap. The flowers of Ragweed most resemble those of other Mugworts and Wormwoods.

Ragweed is an annual and is wind pollinated, the pollen being a potent allergen to those who suffer from hay fever.

As a Metallophyte which is capable of absorbing and hyperaccumulating certain metals from the soil, Ragweed can be employed as a phytoremediator to decontaminate soils, providing that, once it has grown, it is cropped and disposed of safely! This procedure will have to be repeated over a number of growing seasons for it to have any noticeable effect on the contamination. Unless, of course, the only reason for growing something which will tolerate the lead contamination is to cover the otherwise bare ground where few other plants will grow. The latter has the benefit of stabilising the soil against being wind-blown elsewhere. In the case of Ragweed, it is capable of hyperaccumulating the metal lead. Your Author does not know if Ragweed is employed for its metallophyte properties in the UK, but it might be elsewhere in the World where it is more rampant. It is relatively scarce in the UK perhaps because our climate is not inducive to it becoming a rampant weed like it is in some European countries or the Northern Territories of the USA.

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Ambrosia artemisiifolia

Daisy & Dandelion Family [Asteraceae]