Ambrosia artemisiifolia

Daisy & Dandelion Family [Asteraceae]

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Pappus: pappusZpossible none, fruit a hard ridged bur 4-5mm, yellow spines
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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. The leaves are mostly opposite each other but are alternate near the top of the plant.

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 with five thin 'filaments' are suspended. [These 'filaments' are not part of the stamens, but rather thin extensions of the disc-floret tube - which, with this plant being monoecious, ] The stem has long yellowish un-straight hairs, as do the bracts. All the flowers here are male.

The female flowers (your Author cannot find any examples in the photographs) occur singly in the axils of leaf-like bracts and are not recognisable as flowers in the generally accepted parlance. They are greenish with a flat receptacle and have scales but no parachuted hairs for the seeds.

Unknown date, Unknown place Photo: Wikipedia
Female flowers inconspicuous? Really? The female flowers, nestling as they do just above a bract beneath the spike of male flowers, are quite conspicuous, particularly with those two very long white styles which emerge from something shaped like a tiny cream-coloured narrow 'flower vase' (with reddish marks).

4th Sept 2012, Coalville, Leicestershire. Photo: © Chris Cafferkey
The leaves are deeply pinnately lobed with blunt lobes similar to many Wormwoods and Mugworts which belong to the same Artemisia species. Larger leaves, like this one, are bipinnately lobed.

4th Sept 2012, Coalville, Leicestershire. Photo: © Chris Cafferkey
Half a leaf. The central white vein widens as it nears the main stem of the plant.

4th Sept 2012, Coalville, Leicestershire. Photo: © Chris Cafferkey
The stems have long hairs curled predominantly upwards, it seems. Shown here are two branches with a leaf stalk peeling off just below them. These leaf stalks are wide and wrap ~halfway around beneath the bottom of the branch.

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 beneath a bract which acts as an umbrella (but protection from sun or rain or both your Author knows not).

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. It is to be found most concentrated around the London area, but occurs as far north as in Scotland. It grows in dockyards, disturbed ground, arable fields, rubbish tips and other sorts of waste ground. Also in places where birds seed is scattered about.

It is monoecious with separate male and female flowers on the same plant. The male flowers are in upside-down heads between 3 and 5mm in diameter in long slender spikes of flowers. The female flowers are far less conspicuous being at the bases of the upper leaves (your Author has looked and cannot see any in these photographs - so he has borrowed a photo from wikipaedia).

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.

Ragweed contains the secondary metabolites called Psilostachyins, namely Psilostachyin A, Psilostachyin B and Psilostachyin C (which are sesquiterpene dilactones - well - two of them may be, the third seems to be a mono-lactone). But your Author gave up trying to draw these three chemical structures when the available drawings on the web contradicted each other, using differing chemical structures! Which is not unusual.

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Ambrosia artemisiifolia

Daisy & Dandelion Family [Asteraceae]