Some similarities to : Many other
Uniquely identifiable characteristics
Distinguishing Feature : The shape of the cyathia and the stance and length of their horns.
Not to be confused with : the almost extinct (in the UK)
Purple Spurge [which has a similar specific epithet in the scientific name (Euphorbia peplis) - being almost the same spelling as Euphorbia peplus].
A small multi-branched mid-green plant which is a ubiquitous garden or arable weed familiar to many gardeners and farmers. Like all Spurges, Petty Spurge has a toxic milky latex or sap which is both toxic to ingest and caustic on the skin, inducing contact dermatitis and skin-reddening. Different spurges possess slightly differing toxins, some much more toxic than others! Those in Petty Spurge are rather mild in comparison to some other Euphorbs, such as the
Pencil Tree, a non-native. A characteristic of Euphorbs are the toxic Phorbol esters. The milky sap of Petty Spurge has long been used to treat warts and freckles (one citation refers to its ability to treat 'sun-spots' although from a distance of 93 million miles this seems highly unlikely :-)).
The sap of Petty Spurge contains mostly di-terpenes of three differing types: the Jatrophane, the Pepluane (which derive their name from Petty Spurge, (Euphorbia peplus and the Ingenane types. The first two types do not induce inflammation, but the third type, the ingenane di-terpenes are responsible for the irritant and carcinogenic properties of the milky sap from Petty Spurge.
The pepluane di-terpenes are represented by both pepluane and one of its esters pepluanone, which displays anti-inflammatory properties. Petty Spurge also contains the non-irritant Jatrophane esters (which are Lathyranes but without a cyclo-propane ring).
ingenanes are diterpenes and include 5-deoxy-ingenol which can cause conjunctivitis if it enters the eye, 20-deoxyingenol 3-O-angelate and ingenol. The most active constituent is the ingenane di-terpene ester Ingenol-3-angelate, an irritant and a co-carcinogen.
Ingenol-3-angelate, an activator of the enzyme Protein kinase C (PKC), has medicinal properties, and is active against a wide variety of cancers including leukaemia, actinic keratoses and basal cell carcinomas (a non-melanoma skin cancer). Petty Spurge is now cultivated commercially in Australia for the extraction of Ingenol-3-angelate (aka Ingenol Mebutate) (better known as PEP005 in pharmacology) for use as a drug against cancer. A gel form of the pharmaceutical has been approved by the FDA and EMA for the treatment of actinic keratosis - brown patches that occur on the skin of mainly fair-skinned people in response to sun-burn from UV radiation. It is fairly effective but can cause side effects such as runny nose, headache or eye irritation in about 2 or 3% of users. Some folk are also allergic to it and can develop shingles. Another property is that it can re-activate any dormant HIV virus hiding away in the body, thus enabling anti-retroviral drugs to see the virus and kill of any remaining traces, thereby hopefully providing a permanent cure for HIV.
The active cyclo-propane ring is shown in red, carbon numbering in blue.
The latex of Petty Spurge contains a plethora of other compounds including the plant steroidal tri-terpenoids cycloartenol, obtusifoliol and their derivatives. Cycoartenol is a ubiquitous plant steroid that is mandatory in plants in order for them to synthesise other steroids, amongst them the toxic Sitosterol although the author can find no reference that this steroid is present in Petty Spurge - it is just shown for comparison. It will be noted that cycloartenol has an energetic strained cyclo-propane ring, depicted in red, which is likely to make it toxic and which the other sterols shown here lack. The angle between carbon atoms in cycloPropane is 60° (which is 49° more than the ideal 109° angle for C-C bonds), so the ring-strain is considerable. But not only does it possess ring-strain, it also has torsional strain because, with only 3 atoms in the ring, it is necessarily planar but does not want to be. Carbon likes to have all 4 bonds directed towards four corners of a tetrahedron, as in
methane, CH4. These strains will be present in all compounds with cyclopropane rings, including the ingenols shown above, and this makes the ring relatively unstable, and likely to break when disturbed releasing a lot of energy.
Obtusifolia is another plant steroid produced by Petty Spurge and which is found in some vegetable oils.
The toxic β-Sitosterol is also produced in Tansy, Cultivated Flax and Stinging Nettle.