Uniquely identifiable characteristics
Distinguishing Feature : The black and white markings on the wings (petals), with the black being very rare amongst wild plants.
One of the very few wild flowers with black flowers (or at least black patches with purple splodges, on a white base).
Like all members of the pea family, the Broad Bean plant has the ability to fix nitrogen directly from the air in the soil, a remarkable feat most other plants outside the Pea Family lack. The biological nitrogen fixation is accomplished by symbiotic bacteria living in the nodules on the roots. These bacteria are sensitive to oxygen, requiring the absence of it. Plants in the Pea Family are therefore thus almost self-fertilising, not requiring additional nitrogen fertilisers.
The majority of plants that are not in the Pea Family that have nitrogen fixing bacteria are trees or shrubs, of which Sea-Buckthorn is one. Plants with nitrogen-fixing root nodules are called Actinorhizal.
Broad Bean also has the ability to tolerate normally toxic levels of aluminium in the soil, in fact it not only tolerates it but hyperaccumulates aluminium. It is thus a valuable metallophyte for the phytoremediation of contaminated land, able to mop up aluminium from the soil. Note that to remove the entirely, the plant then has to be harvested and disposed of safely elsewhere. The whole cycle has to be repeated over several seasons to bring heavy metal contamination down to safe levels. By reverse reasoning, it is un-wise to grow Broad Bean for human consumption on soils containing high levels of aluminium, although aluminium as a metal is well tolerated by both plants and animals. However, many species are sensitive to soluble aluminium, which can be highly toxic under certain conditions. The acidification of soil is causing the normally insoluble aluminium in the soil to become soluble, and this can give rise to the death of some trees, especially conifers, and other plants.
Those photos with smaller pods, such as the photos from those in a field near Rufford, are probably Field Beans (which have the same botanical name, Vicia faba). Field Bean is often grown as a farm crop, and depending upon their variety and size, are sold either as food for racing pigeons or for a foodstuff eaten in the Middle East.
The flowers are scented with a smell similar to that of Apple Blossom, and when growing as a large field can be smelled from a distance.
The seeds of Broad beans contain the toxins
convicin (a mixture of glucosides of pyrimidines)
lectins, and Vicioside. To a much lesser extent other parts of the plant also contain these toxins. Agriculturalist try to minimise the amount of toxins within the broad beans themselves by the cross-breeding of different varieties. Note the number of nitrogen atoms is high in relation to the number of carbon atoms for the pyrimidinone base.
Vicioside (or Vicine) is the glycoside of a pyrimidinone. Within the body glycosides can easily lose the sugar molecule leaving the pyrimidinone naked. Vicine is toxic and causes the disease called favism but only in people who lack the enzyme GPDG (glucose-6-phosphate dehydrogenase) [an inherited condition]. Symptoms of favism include headache, dizziness, vomiting, fever and anaemia leading to possible death. The aglycone of Vicine is called
Divicine, which seems to imitate an amino acid, but one that does not code for a protein; it is therefore called a non-proteinogenic amino acid (NPAA). Divicine is found in two tautomeric forms, one based upon pyrimidine, the other based upon pyrimidinone. Divicine is the haemotoxic component of Broad Beans which plays a role in favism.
Both Broad Beans and Common Vetch (Vicia sativa) contain an analogue of Vicine called
Convicine, which is a glucoside of
Isouramil, into which Convicine decays. Isouramil is also a haemotoxin.
Wyerone (and Wyerone Acid) are acetylenic furanoid ketoesters possessing a highly energetic triple bond, unusual but not unique in the plant kingdom. Naturally it is poisonous with anti-fungal properties. Although it is found within the shoots of Broad Beans, it is synthesized in greater concentrations by the plant in response to a fungal infection; it has anti-fungal properties. Wyerone is a phytoalexin (a microbial stress compound - something which is synthesized in response to an external biological attack).