Distinguishing Feature : The soapy feeling of its sap and leaves.
Not to be confused with: White Soapwort (Gypsophila radix [non-native] or
Baby's Breath Gypsophila paniculata) [found in the UK] which have similar soapy saponins.
Soapwort was once used extensively to make soap especially for use by woollen mills, but the soap so produced is now only used for delicate cleaning operations such as those performed by museum conservationists, such as for cleaning the Turin Shroud. Its leaves have a very soapy feel to them because of the presence of saponins. They also contain a fungicide, which helps preservation. Because of its industrial past, it is found quite extensively now growing wild in grassy places, the banks of streams, near canals, on on hedge banks. Despite its poisonous nature it has in the past been used to make a head on beer.
The stems are thick, hollow and rather brittle. The five petals, although symmetrically arranged around a circle at 72 degree intervals, are usually asymmetric. Sometimes with slight negative curvature at the tips (slightly nicked at the tip). Soapwort spreads rapidly by means of underground rhizomes.
There are about 20 species of Soapworts, only three of which occur in the UK, one of which is
Rock Soapwort. The genus Saponaria is closely related to the genera Lychnis and Silene, but Soapworts have only two styles in the flower rather than the three or five respectively of the others.
Because of the presence of triterpenoid saponins, such as
saponarioside A, B (major) and C, it is, like solanine and digitoxin which are also saponins which are poisonous, destroying red blood cells. Saponins generally are usually highly polar molecules. Soapwort contains triterpenoid saponins called saponariosides (sometimes called Gypsogenin Saponins presumably from their first identification in Gypsophila species?), specifically eleven of them labelled as saponariosides C to M. All act to lower surface tension and will haemolyse blood cells. Unfortunately the author cannot find a single structural formulae for any of these thirteen Saponariosides!
It has been determined that the maximum safe intake of the plant Soapwort is 100mg/day. Saponins are toxic.
The seeds of Soapwort contain Saporin which is a protein called a ribosome inactivating protein (appropriately acronymed to 'RIP'). It inhibits protein synthesis within cells. RIPs are some of the most toxic molecules known and amongst their clan are such notorious molecules as
Abrin, but they do not occur in Soapwort). However, saporin is high in toxicity, amongst the highest of all RIPs, but thankfully is not able to freely enter cells on its own. Saporin should not to be confused with saponins. Saporin has remarkable stability and is able to resist denaturation and proteolysis. It may well have pharmaceutical applications.
Bouncing Bett is a double-flowered version of Soapwort, and is more likely to be found in a garden setting than is Soapwort.
Soapwort usually has its blooms closed in the daytime, opening up only in the evening. Vespertine is the name given to this behaviour.
Comparing the steroidal component (ignoring the four sugar units) with that from Tomatine, there there is an oxygen atom in Saponoside A which substitutes the nitrogen atom in Tomatine (in the six-membered spiro ring [top right]). This makes Saponoside A non-alkaloidal, unlike Tomatine.
Compare Quillaic Acid with Oleanolic Acid, another acidic steroidal molecule. Quillaic Acid is named after a South American tree called Soap Tree (Quillaja saponaria it was first found in. The majority of saponins in Soapwort have Quillaic Acid as the aglycone (steroidal base). Quillaic Acid saponins are generally utilised by the plant as defense cheicals against herbivores, but they are ineffective against those that have developed resistance to them, as some herbivores do.