乌羽玉（学名：Lophophora williamsii）是一种细小及无刺的仙人掌。 它们原产于美国德克萨斯州西南部至墨西哥，主要在奇瓦瓦沙漠、塔毛利帕斯州及圣路易斯波托西州生长。

乌羽玉含有精神生物碱，如麦司卡林（三甲氧苯乙胺）等，故被用在宗教致幻剂及多种宗教超越上，包括冥想及迷幻药治疗法等。美国原住民很久以前就已经使用乌羽玉作为仪式及医药用途。乌羽玉于3月至5月间开花，有时会开至9月。其花朵是粉红色的，花药有趋触性。

Lophophora williamsii /loʊˈfɒfərə wɪlˈjæmsiaɪ/ or peyote (/pəˈjoʊti/) is a small, spineless cactus with psychoactive alkaloids, particularly mescaline. The English common name peyote comes from the like-spelled Spanish name, which in turn comes from the Nahuatl name peyōtl [ˈpejoːt͡ɬ], said to be derived from a root meaning "glisten" or "glistening". Other sources translate the Nahuatl word as "Divine Messenger". Native North Americans are likely to have used peyote, often for spiritual purposes, for at least 5,500 years.