Real Dictionary

umbel in American English
a cluster of flowers with stalks of nearly equal length which spring from about the same point, like the ribs of an umbrella
noun: an inflorescence in which a number of flower stalks or pedicels, nearly equal in length, spread from a common center

umbel in British English
noun: an inflorescence, characteristic of umbelliferous plants, in which the flowers arise from the same point in the main stem and have stalks of the same length, to give a cluster with the youngest flowers at the centre