Ulva

Uncommon

(ophioglossales)

Understory

Unfertilized ovules

Unicellular

Composed of only one cell.  Many of the algae, particularly the diatoms are unicellular, or composed of single cell.

Unisexual Flower

Unlike Molecules

Upper Lip

Upright

Urediospores

                    DIAGRAM:  

                          PHOTO:  Puccinia / Puccinia / Puccinia / Puccinia / Puccinia

Urn-shaped