Yarrow (Achillea millefolium) flowers June – November so its blooms still brighten campus grasslands. 
Typically of the Asteraceae, Yarrow `flowers’ are clusters of tube-florets surrounded by 5 ray-florets masquerading as petals. These capitula gather further into dense heads, or corymbs, resembling the umbels of the Apiaceae (ex-Umbelliferae). Also like several umbellifers (e.g. Angelica, some Hedge Parsleys and Burnet Saxifrages), Yarrow’s flower-colour ranges from white to pink and even purple. Finely divided, bi- or tripinnate leaves (millefolium=`thousand leaves’) complete a superficial resemblance to many Apiaceae. Coincidence or convergent evolution? On campus, Yarrow certainly occupies similar niches to some umbellifers, even mingling with Wild Carrot, Daucus carota (below right: with Ribwort Plantain as well):
What determines Yarrow’s flower-colour?
From white to pink and dark pink
Plants spread by stolons to create same-coloured clonal patches, but neighbouring patches can differ greatly, as if some had been splashed with blood. Perhaps this led -by `sympathy’ – to the old medicinal use of Yarrow to staunch bleeding (alternative names: Staunchwort and Carpenter’s Weed). In `Wild Flowers of Britain’, Phillips explains `Achillea’ by Achilles’ use of Yarrow to treat his warriors’ wounds. Much good did it do him….
(All pictures copyright D. Solomon)