Yes, in fact there are many! Usnea (a lichen that looks similar to the moss on live oak trees; Urtica dioica, which is Stinging Nettle; Ulmus Fulva which is also known as Slippery Elm. If you were looking for herbs with common names starting with the letter U, rather than their botanical binomials starting with U, here's a few of those: Umbrella Grass, Umbrella Tree, Unicorn Root, Uva-ursi.
Plants that begin with the letter U:
Ugly fruit (a citrus hybrid)
Ugni molinae (Chilean Guava)
Ulmus (elm)
Umbrella plant (Schefflera arboricola, Darmera peltata, and others)
Umbellularia californica (California Laurel)
Urn plant
Urtica
Uvularia
· Urginea
· Ursinia
uranis
Umbrella plant, urginea and ursinia are flowers. They begin with the letter U.
Urginea and Ursinia are flowering plants. They begin with the letter u.
umbrella plant
urn plant
Umbrella plant
Utopian Irrelevance
'You' is not a letter it is a word.
urad beans
Undhiyu
· ugli fruit, uvilla
Uvilla is a fruit. Ulluco is a vegetable.
No, a car is not a vegetable and you know it.
A vegetable starting with D is dandelion.
Ita palm is a fruit. Iceberg lettuce is a vegetable.
Turnip
quadrifoliate
kangkung
asparagus artichoke
Asparagus
asparagus
· ulluco