If you are a gardener you will be very familiar with sun spurge (Euphorbia helioscopia) as it is a common 'weed' of cultivated areas and it spreads willingly growing in the most unlikely places; sometimes where there is hardly any soil, even in cracks by brick walls! Specimens growing in poor or little soil tend to be much smaller than those growing in fertile soil.
It mainly flowers from April to July but it does flower on until November in good years and it can be seen in a 'leafy' state throughout the winter visible in gardens all year round. It is quick growing and soon reappears after you pull a load out! Apparently the seeds are spread by ants.
If you break or cut the stem you will find a white latex fluid seep out and this leads to an old country name of umbrella milkweed. Sun spurge is a highly poisonous plant and some ingredients are extracted for use in the pharmaceutical industry.