HOGWEED

COW PARSNIP

Heracleum sphondylium

Carrot Family [Apiaceae]  

month8May month8jun month8june month8jul month8july month8Aug month8sep month8sept month8Oct month8Nov

status
statusZnative
 
flower
flower8bicolour
 
flower
flower8white
 
inner
inner8pink
 
morph
morph8actino
 
morph
morph=HemiZygo
 
petals
petalsZ5
 
type
typeZclustered
 
type
typeZumbel
 
stem
stem8round
 
stem
stem8ribbed
ribbed
stem
stem8hollow
hollow
contact
contactZhigh
 

24th Oct 2007, River Dee, North of Farnden, Near Chester. Photo: © RWD
Can grow up to 3m high, but rarely seen over 2m.


25th May 2005, Reddish Vale, Greater Manchester. Photo: © RWD
A youngish plant, without flowers. Stems purplish, with inflated bracts under the branches.


25th May 2005, Reddish Vale, Greater Manchester. Photo: © RWD
An even younger plant, without flowers. Leaves with wide and angular lobes, as if trying to emulate a space-filling Sierpinsky curve. The leaves on Hogweed are a slightly duller green than those of the similar Giant Hogweed.


24th Oct 2007, River Dee, North of Farnden, Near Chester. Photo: © RWD
Both pinkish lilac and white umbels can appear on the same plant in a cluster of clusters.


24th Oct 2007, River Dee, North of Farnden, Near Chester. Photo: © RWD
Both red and white umbels can appear on the same plant.


24th Oct 2007, River Dee, North of Farnden, Near Chester. Date, place, where Photo: © RWD
Many specimens have white flowers.


24th Oct 2007, River Dee, North of Farnden, Near Chester. Photo: © RWD
Flowers are usually white, but sometimes pink or even purple as here. Flowers have five petals, the inner are symmetrical and actinomorphic in form, the outer Zygomorphic with much larger petals on the outer edge of the umbel. The central flowers are yet to open and appear a deeper red.


17th June 2011, Paterdale, Cumbria. Photo: © RWD
The petals are notched; the outer ones especially deeply cleaved.


17th June 2011, Paterdale, Cumbria. Photo: © RWD
A flower near the centre is is hemi-zygomorphic, nearly actinomorphic but not quite. Five stamens, most having lost their grey coloured anthers. A green or white ovary in the centre of each flower with two cylindrical prongs sticking out.


17th June 2011, Paterdale, Cumbria. Photo: © RWD
The petals directed towards the centre of the umbel have opened up in this plant. Outerward petals deeply cleft.


24th Oct 2007, River Dee, North of Farnden, Near Chester. Photo: © RWD
Stem ridged, shortly hairy, sometimes reddish. An inflated bract beneath any branch ending in a trefoil leaf.


5th Aug 2004, Near Cark, Cumbria. Photo: © RWD
Leaf shape highly distinctive of Hogweed, quite different from those of Giant Hogweed. Sometimes the leaves have a speckled appearance.


5th Aug 2004, Near Cark, Cumbria. Photo: © RWD
Sometimes the leaves have a speckled appearance.


24th Oct 2007, River Dee, North of Farnden, Near Chester. Photo: © RWD
Other times not.


24th Oct 2007, River Dee, North of Farnden, Near Chester. Photo: © RWD
What is destined to become the seed pod is just below the petals and is covered in short white hairs.


21st Aug 2004, River Kent, Cumbria. Photo: © RWD
The seed pods are flattened and oval.


27th June 2009, Blackleach Country Pk, Walkden, Gtr M/cr. Photo: © RWD
Un-ripe seed pods.


27th June 2009, Blackleach Country Pk, Walkden, Gtr M/cr. Photo: © RWD
Still hairy.


1st Aug 2007, Anglezark Reservoir, Belmont, Lancashire. Photo: © RWD
The seed pods are oval and flattened, with wings and dark streaks. Two short projections point in opposite directions atop.


31st july 2011, Moses Gate Country Park, Bolton, Lancs. Photo: © RWD
The ripe fruits. Each parallel pair contain one seed, 2 seeds per flower. The long curved brown teardrop shapes are oil ducts, mostly in 4's but some in pairs, they are not seeds.


31st july 2011, Moses Gate Country Park, Bolton, Lancs. Photo: © RWD
Fruits very flat, an identifying feature of Hogweed.


31st july 2011, Moses Gate Country Park, Bolton, Lancs. Photo: © RWD
Two stigmas still attached at top and at 6mm long are much shorter than the long ones attached to the fruits of Giant Hogweed. The fruits are heart-shaped, slightly longer than wide with a wide flange around the periphery. The brown curved teardrop shapes within each pair of mericarps are oil ducts, not seeds and are narrower than the corresponding ones in Giant Hogweed. There is only one seed per mericarp, the same as for Giant Hogweed.

(The fruits of Giant Hogweed are larger (10-14mm) and more elliptical)


Hybridises with : Giant Hogweed (Heracleum mantegazzianum) to produce Heracleum sphondylium × mantegazzianum.

Some similarities to : Giant Hogweed but Hogweed is only half as tall at up to 2 or 3 metres, the flower umbels of much smaller diameter, and the fruits are wider. The leaves of Giant Hogweed are not only larger, up to a metre long, but differ in form being more fan-shaped, rather than having great chunks missing from the edges which is what Hogweed looks like.

The flowers of Hogweed, unlike those of Giant Hogweed, can sometimes have a pinkish or purplish colour. Sometimes both white and pink flowers can be on the same plant, but on differing umbels. The straw-coloured seed pods are flattened and oval, with four streaks radiating downwards from the top.

Not to be confused with: Cow Parsley (a member of the same family and similar name) nor with Cowslip [a plant of similar name but which belongs to the Primrose family].

Uniquely identifiable characteristics

Distinguishing Feature : The shape and size of the lower leaves give it away. These leaves are quite distinct from the leaves of Giant Hogweed, which are also very distinguishable.

Hogweed (and Wild Parsnip) has much the same furocoumarins as does Giant Hogweed, and as such any sap on the skin can give rise to the same photodermatitis, where subsequent exposure of the skin to sunlight will lead to an intense itching and burning sensation leading to the formation of wheals which can be slow to heal. See Giant Hogweed for more details and structural chemical formulae. Treatment can be very difficult as skin-contact with furocoumarins often causes necrosis from which a secondary bacterial infection is typical. A strong hyper-pigmentation of the scarred flesh can remain for months or even years afterwards.

Furocoumarins cause effects on DNA similar to those of Yperit, a chlorinated Mustard Gas called Sulfur Mustard with the formula Cl-CH2-CH2-S-CH2-CH2-Cl which was developed by the Germans for use in WWI. Sulfur Mustard, like furocoumarins, alkylates a nucleic-acid in strands of DNA (in this case guanine rather than thymine of furanocoumarins [see below]) leading to cell apoptosis and possibly cancer later on in life. The major adduct in the case of Sulfur Mustard is 7-(2-HydroxyEthyl-ThioEthyl)-Guanine and accounts for about 60% of the total alkylation.

MODUS OPERANDI of FUROCOUMARINS


COUMARINS and FUROCOUMARINS


First of all, a furocoumarin (aka furanocoumarin) is a coumarin, such as Umbelliferone shown, but with the addition of a fused furan ring. This addition makes furocoumarins far more toxic than are coumarins. The furocoumarin shown is that of the simplest, Psoralen. There are many others with side groups attached, or with the furan ring attached at the lower angle as shown for Angelicin which are known as angular furocoumarins (as opposed to linear furocoumarins like Psoralen). With this in mind, the next paragraphs will show (by example with Psoralen, but in reality any furocoumarin will behave similarly) how furocoumarins can interact with DNA and cause havoc in the body.


THE FOUR NUCLEOBASES


Thymine, (not to be confused with Thiamine, the sulfur-containing Vitamin B1) is also known as 5-methyluracil is one of the four Nucleobases found in DNA. The four bases are Guanine, Cytosine, Adenine and Thymine, abbreviated to G, C, A and T in genomic representations of the DNA. Thymine, 5-MethylUracil, is shown below in red. Both Cytosine and Thymine are Pyrimidines with but a 6-membered ring, whilst both Guanine and Adenine are Purines (with fused pyrimidine and imidazole rings). In the coding part of DNA specific Purines pair up with specific Pyrimidines. Thus Cytosine is paired up (by three hydrogen bonds) with Guanine, and Adenine (with but two hydrogen bonds) with Thymine. [In RNA, another pyrimidine, Uracil, takes the place of Thymine, and pairs with Adenine].

THYMINE and THYMINE DIMERS


Of those four, Thymine readily dimerises under the action of ultraviolet light, either with a bridging cyclobutane linkage, or with just a single bond between the two Thymine units. Two molecules of Thymine sited in close proximity on the DNA will even dimerise when in-situ when on the DNA, and when it does so, can cause havoc by preventing the proper reading (when constructing proteins for example) or copying of the DNA.


DNA ADDUCTS WITH FUROCOUMARINS

Furocoumarins have highly reactive double bonds on both the Furan ring and the Lactone ring which are excited by UV light. When furocoumarins enter skin cells (such as may occur when touching Hogweed or Giant Hogweed) those furanocoumarins are then activated by UV light in sunlight and they will form similar links with Thymine in DNA. The furocoumarins can bond a thymine molecule in one of two differing positions. Mono-Adduct A shows the thymine bonding to the coumarin part, whilst Mono-Adduct B shows it bonding to the furan ring of the furocoumarin. The R- shows where the Thymine bonds to the DNA molecule.


Three DNA Adducts are shown here. The Bi-Adduct shows it forming a bridging link between two Thymine molecules on the DNA, completely fouling the DNA tying the two strands (or two parts of the same strand) together. Naturally, this is not good news for the well being of the person exposed to furocoumarins in the environment.

Not only can furancoumarins bind to DNA through alkylation which leads to mutations, but they can also bind to proteins resulting in allergies. Both processes lead to apoptotic cell death, cause skin cancer and tumour of the kidneys in animals. In the liver Furocoumarins are metabolised to highly reactive intermediates called epoxides which can also bind to both DNA and to proteins. High doses of furocoumarins are therefore also toxic to the inner organs as well as to skin.

FuroCoumarins can also intercalate between the strands of DNA, meaning that they do not chemically bind to it (except perhaps by very weak hydrogen bonds) but rather they remain intact, where nevertheless they are still capable of causing so-called 'frame-shift' mutations. Other alkaloids which can intercalate between the strands of DNA include Emetine, Sanguinine, Berberine, Quinine, β-Carboline and FuranoQuinoline alkaloids.


PHARMACEUTICAL USES OF FUROCOUMARINS

Furocoumarins, for example 8-Methoxypsoralen, were used medicinally to treat psoriasis. In applying it to the skin they exploit that very same ability of furocoumarins to kill the proliferating keratocytes present in psoriasis sufferers when irradiating by UV light. However, furanocoumarins can also induce cancer, so this treatment has been superseded by safer alternative therapies.


ERRORS IN DNA and RNA CODING

Thymine seems to be the achilles heel of DNA, its propensity to glue strands of DNA together can lead to both mis-constructed proteins and to mutations. How it ever came to have such an important role taking a part in the coded of our genes is astonishing for a molecule that is apt to put a spanner in the works when the genes require decoding. The Author thinks it possible that it is at least partly instrumental in the evolution of species and without it evolution may not have proceeded so fast. However, it turns out that much of human evolution is due to mutations in the genome that do not occur in those regions coding for the genes themselves, but rather occur in those much shorter regions encoding for promoters and enhancers of those genes. There are about 44,000 enhancers and 180,000 promoters, short regions in the genome that interact and control gene expression within particular cells the human body. Some of these promoters and enhancers control what type of cell that the cell will become. Mutations in the genetic composition of these small promoters and enhancers is responsible for most human diseases that have a genetic origin, including many cancers.

However, Thymine is not the only nucleobase with a personality disorder. Cytosine itself (which pairs with Guanine in DNA - both drawn above) is apt to lose an amine group in exchange for an oxygen atom when it then becomes Uracil, the pyrimidine used in RNA but not DNA. This accident is not uncommon - occurring at a frequency of about 1%. If this occurs in DNA, then the presence of an errant Uracil nucleobase will probably be recognised by an automated repair mechanism effected by the enzyme Uracil Glycolase and corrected back to the appropriate Cytosine. If not repaired, the errant Uracil leads to a point mutation. If, however, Cytosine becomes Uracil in RNA (rather than in DNA as above), then this error cannot be corrected (since Uracil is allowed, being one of the four coding nucleobases in RNA) but it will not matter as much: RNA is comparatively short-lived and doesn't store the genome, it is the blueprint for constructing proteins.

Cytosine within DNA can also be methylated by the enzyme DNA Methyltransferase, when it then becomes 5-methylcytosine. Adenine within DNA can also be methylated (to 6-methyladenine). These methylations (and acetylations which are implemented by other mechanisms) are instrumental in epigenetic changes to the genome, affecting evolution (they can be inherited by cell division). However, most of those effects have nothing to do with furocoumarins or Hogweed.


  Heracleum sphondylium  ⇐ Global Aspect ⇒ Apiaceae  

Distribution
family8carrot family8Umbelliferae  family8Apiaceae

 BSBI maps
genus8heracleum
Heracleum
(Hogweeds)

HOGWEED

COW PARSNIP

Heracleum sphondylium

Carrot Family [Apiaceae]  

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