Identify a euphorbia from a photo
Photograph the plant and find out which euphorbia it is, whether it is a garden plant or a weed, and how to handle the sap.
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The sap, first
Euphorbia sap is a milky white latex, and it is present in the stems, leaves and roots of almost every species. It is not poisonous in the sense that a berry is poisonous. It is caustic, which is a different and in some ways more immediate danger.
On skin it causes contact dermatitis, blistering and a rash that can last days. In the eye it causes severe pain and can cause permanent damage, and there are documented cases of vision loss. The sap of some species is under pressure and squirts when a stem is cut.
Pruning is therefore the dangerous activity, not walking past the plant. Wear gloves and glasses, cut on a cool day when the sap is less mobile, and wash any skin contact immediately with plenty of water. If it gets in an eye, irrigate and get medical help.
The other thing worth knowing: do not burn euphorbia prunings. The smoke carries the irritant compounds and can cause serious respiratory injury.
The cyathium, which confirms the genus
Euphorbia flowers are not flowers in the ordinary sense. What looks like a single flower is a cyathium: a small cup of fused bracts containing one female flower reduced to an ovary and several male flowers reduced to single stamens.
In many of the common euphorbias, the bracts are a bright acid yellow-green, and that is what people mistake for petals. It is why the euphorbias were once called spurge — the colour and shape look like a flower but are structurally something else.
Once you have seen a cyathium under a hand lens or in a close photo, you can identify the genus with confidence even when the species is unclear. Nothing else in a garden has that structure.
For practical identification without a lens, the combination of milky sap, insignificant or acid-yellow flowers and often a head of bracts is enough.
The common euphorbias
| Plant | Type | Look | Where you meet it |
|---|---|---|---|
| Euphorbia characias subsp. wulfenii | Shrubby | Blue-green leaves, huge chartreuse bract heads | Garden borders, very common |
| Euphorbia myrsinites | Ground cover | Sprawling stems, fleshy blue leaves | Rock gardens and gravel |
| Euphorbia pulcherrima (poinsettia) | Poinsettia type | Red bracts, soft green leaves | Indoors at Christmas |
| Euphorbia peplus (petty spurge) | Weed | Small, pale green, tiny rounded leaves | Garden beds, cracks, pots |
| Euphorbia helioscopia (sun spurge) | Weed | Broader leaves in a whorl under the head | Arable land and disturbed ground |
| Euphorbia lathyris (caper spurge) | Weed | Tall, narrow opposite leaves in a cross | Gardens, often self-seeded |
| Euphorbia tirucalli (pencil cactus) | Succulent | Leafless green cylindrical stems | Houseplant and warm climates |
Garden plant or weed
The distinction matters because the advice is opposite. Garden euphorbias are grown deliberately and are worth keeping, with care. Weed spurges come up everywhere and should be pulled young.
Petty spurge is the one most people meet without realising. It is a small, pale, upright annual with tiny rounded leaves and minute green flowers, and it turns up in bare soil, in pots and in cracks. It is genuinely a weed, and it produces seed fast.
Sun spurge and caper spurge are larger and showier. Caper spurge is sometimes grown deliberately as a curiosity, and there is an old story that it repels moles, which has no basis I have ever found.
For weed spurges, pull them before they set seed. Wear gloves. Do not strim them, because the sap sprays. And do not put them in the compost if you have a hot compost system that will not kill the seed — they will be back.
Reading the plant in a photo
- The sap. If there is a white mark where a leaf has been broken, that is the confirmation. It is the fastest test and the one that requires gloves.
- The bracts. Acid yellow-green, forming a cup or a rounded head at the top of the stem.
- The leaf arrangement. Many euphorbias hold their leaves in a whorl just below the flower head, which is a recognisable pattern.
- The leaf shape. Petty spurge has tiny rounded leaves; characias has long narrow blue-green ones; poinsettia has soft scalloped green ones.
- The stem. Euphorbia stems are often thick, fleshy and pale, and some succulent species are entirely leafless and cylindrical.
- What it is not. The main confusion is with yellow-flowered sedums, which have ordinary five-petalled flowers and no milky sap at all.
I pruned a Euphorbia characias without gloves on a hot afternoon, and by evening I had a line of small blisters up my forearm where the sap had run. It took a fortnight to heal and it left a mark for months.
That is the thing about euphorbias that catches people out. They are ordinary garden plants, sold in every nursery, and they look harmless. The sap is a caustic latex, and it does not need much contact to do damage.
This page covers both halves of the problem: which euphorbia you have, and how to handle it without getting burned.
Frequently Asked Questions
Break a leaf stalk and look for milky white sap, which confirms the genus. Then look at the flower structure: what appears to be a single flower is a cyathium, a cup of fused bracts with acid yellow-green colour and no true petals.