Easily semantically confused with : the Genus
Senna [which although belonging to the same Pea (Fabaceae) family, are not Senna plants but look fairly similar and the flowers, although yellow, are a totally different shape]
Not to be semantically confused with : the Genus
Cotula [plants belonging to the Buttonweeds Genus (in the Asteraceae family)]. Nor with Bladder Campion (Silene vulgaris) which belongs to another differing family, the Pink & Carnation Family (Caryophyllaceae)
Easily mistaken for :
Orange-bladder Senna (Colutea × media) [being the hybrid between Bladder Senna and the non-native Colutea orientalis].
Orange-bladder Senna differs from Bladder Senna in that the flowers are an orange-bronze colour with a beaked keel and the pods which split open at the apex.
Uniquely identifiable characteristics
Distinguishing Feature : The inflated seed pods are a feature of all Bladder-sennas, of which there are about 25 species worldwide. However, only the two mentioned above escape into the wild in the UK. But beware Petty Whin (Genista anglica), which although much lower at just over a foot high, also has inflated seed pods, but they are much smaller at only 12 - 20mm long.
Like many plants from the Pea family Bladder Senna contains some quinolizidine alkaloids such as Cysteine, which is poisonous if consumed. It also contains the poisonous Canavanine, a
non-proteinogenic amino acid (NPAA) which is similar to the amino acid L-Arginine.
The shrub is popular in gardens as an ornamental due in part to the unusual and eye-catching highly-inflated seed pods which are filled with a gas. Others say they are filled with a liquid.
Some sources claim that the gas within the seed pods is air, but this seems unlikely seeing as it seems to be pumped inside by the plant, and would probably have an excess or a deficiency in some gas compared with the relative concentrations of the gases which constitute air. Your Author would imaging that carbon dioxide concentrations were anomalous compared to those of air and it might even have some ethylene gas as well, a well known plant hormone produced by some plants. Of course, these gases would eventually diffuse out until it did have the same proportions of gases to those constituting air. If they were initially filled with a liquid, it could be that as the liquid evaporated within the pod, this inflated the pod because gases occupy about 2000-times the volume of liquids, which would neatly explain how the pod becomes so bloated, which is otherwise hard to explain.
The shrubs escape in the UK and are to be found naturalised in waste or grassy places, on railway embankments and beside roads mainly in the home counties but elsewhere scattered about in the UK south of Newcastle.