- ubicuista, ubiquist
- umbela, umbel
- umbelado, umbellate
- umbeliforme, umbelliform, umbraculate
- umbélula, umbellule
- umbilicado, umbilicate
- umbón, umbo
- umbonado, umbonate
- umbrófilo, sciophilous, shade-loving
- uña, claw
- uncinado, uncinate, hooked
- uncinulado, barb
- uncínulo, undulate
- unguiculado, unguiculate, clawed
- uni-, uni-
- unido, affixed, joined, united
- uniforme, even, smooth
- uniformemente, uniformly
- unilateral, one-sided, unilateral, secund
- unisexual, unisexual
- untuoso, greasy, unctuous
- urceolado, urceolate
- urticante, stinging, urent
- utrículo, utricle