Type of inflorescence in which all pedicles (floral stalks) eradiate from a common point. E.g., geranium, gardenia. One can also say the umbel is a raceme whose axis did not elongate: the younger flowers are in the center and the older gradually distal. (Also see Raceme, Inflorescence).
Undulated
Leaf or petal with wavy margin. The term is not applied to serrated or toothed margins.
Unisexual
Monoecious or Dioecious plants in which the flower are male or female; flower that is not hermaphroditic, but is either male or female. (compare with Hermaphrodite).
Petal: Generally the most showy part of the flower. Petals product the core of the flower and, when colorful, serve to attract pollinating insects towards the stamens and pistils. A flower can present few petals, like the flowers of several dayflowers, with only 3 petals) or several (like roses). The group of petals in a flower is called a corolla. (Also see sepal, stamen, pistil, flower and corolla).