Flower of the Yellow Day-lily (Hemerocallis lilioasphodelus). In the background behind the flower are a couple of flower buds that have yet to open.
From Wikipedia (http://en.wikipedia.org/wiki/Hemerocallis_lilioasphodelus):
Hemerocallis lilioasphodelus, (syn. Hemerocallis flava, Lemon Day-lily Lemon Lily, Yellow Day-lily) is a plant of the genus Hemerocallis. It is found across China, in Europe in N.E. Italy and Slovenia and is one of the first daylilies used for breeding.
Hemerocallis lilioasphodelus grows in big spreading clumps and its leaves grow to 75 cm (30 in) long. It has lemon-yellow flowers with a sweet scent in a cluster of 3 to 9 flowers.
The flowers of some daylillies, including Hemerocallis lilioasphodelus are edible and are used in Chinese cuisine and Japanese cuisine.