This must be the most commonly found Euphorbia in most parts of Ireland. It's an upright, hairless, greenish-yellow annual and is found on disturbed ground (and in my garden) and other waste places. Like others in this family, the little flowers lack petals and sepals, instead having a circle of yellowish bracts enclosing a single female ovary which is surrounded by a cluster of male flowers. The leaves are oval, broadest near to the tip. The plant grows to a height of 30-40 cm and usually faces up to the sun, flowering from May to late September. The species name 'helioscopia' is Greek for sun-gazer. The seeds of this plant are 3-lobed capsules which are scattered on the ground when ripe. This plant is highly poisonous, was probably introduced into Ireland and belongs to the family Euphorbiaceae.
I first knew this plant in the 1950's in my parents' garden in Dundrum, Co Dublin. It was photographed in my own garden in Gibletstown, Co Wexford in 2008.
If you are satisfied you have correctly identified this plant, please submit your sighting to the National Biodiversity Data Centre