Weed identification please

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Any ideas?

Can you get a view from the top of the plant? Possibly euphoria?

Euphorbia.

Euphorbia peplus, petty spurge. Less exciting relative of Poinsettia (Euphorbia pulcherrima = "most beautiful")

When you are pulling it up, wear gloves as euphorbia sap is nasty stuff and can damage your skin.

Euphorbia sap can cause photosensitivity - a rash that re-occurs every time that patch of skin is affected by bright sunlight. In my experience it's more of a problem with the larger Euphorbias, the ones that a grown in gardens as ornamentals. Pulling up the tiny ones like E peplus doesn't usually break the stem to release the sap, so, obviously take care, wash sap off immediately should you get some on you, but don't be afraid that some scary out-of-control monster of a plant has invaded your garden.

Agreed. Euphorbia. Became a rampant pest in my garden withing weeks and was seemingly indestructible. My neigbpurs all seem to have the cultivated variety so I dont know if my weedling types are spreading from them. It's a pain.

My neigbpurs all seem to have the cultivated variety so I dont know if my weedling types are spreading from them. No. The garden varieties are different species (E characias, E mellifera, E myrsinites etc), so can no more give rise to seedlings of E peplus than a Siamese cat could give birth to a pure tiger.

E. peplus isn't indestructible. It's a prolific seeder, so will germinate any time you disturb the soil and give it some bare ground to grow into. But it's an annual, so it'll die after flowering, and doesn't put down a big root system, so is quite easy to pull up.

E robbiae and E cyparissias, which spread by runners, are more difficult to control. But they self seed a lot less readily.