There are a surprising number of plants still in flower though they tend to be occasional and not always in the best condition. This is Yarrow Achillea millefolium, a common plant of roadsides and rough grasslands. It has very fine feathery leaves and heads of dirty white flowers that could be mistaken for a member of the Umbelliferae family, but it is in fact one of the Asteraceae (formerly Compositae).
What appears to be an individual flower in the Asteraceae, is actually a dense collection of small flowers or disc florets. What appear to be the petals around the disc florets are called ray florets.
In this photo the large white ray florets are clearly visible but the disc florets are crammed in the centre of the flower head. The large scales that contain the flower head are called involucre-bracts.
Here is an individual disc floret, on the right is the shape of what will be the fruit or achene. This disc floret is tubular and it did have a small scale attached to it at the base which has been removed for the photograph.