萱草（Hemerocallis fulva、Orange Daylily）是萱草科萱草属植物，旧的克朗奎斯特分类法中属于百合科（Liliaceae）。别名众多，有忘忧草、宜男草、疗愁、鹿箭等名。原产于中国、西伯利亚、日本和东南亚，台湾于1661年由华南引入。不可供食用。

黄花菜、金针所指物种为Hemerocallis citrina，与萱草为不同物种。

所属之黄花菜属的拉丁文属名Hemerocallis源于希腊文，表示「一日之美」，以其花一朵多仅开一日为名，从日出开至日落，隔日即换上另一、二朵绽放。多种在盆里用来观赏。

Hemerocallis fulva, the orange day-lily, tawny daylily, tiger daylily, fulvous daylily or ditch lily (also railroad daylily, roadside daylily, outhouse lily, tiger lily, and wash-house lily), is a species of daylily native to Asia. It is very widely grown as an ornamental plant in temperate climates for its showy flowers and ease of cultivation. It is not related to true lilies, but gets its name from the similarity of the flowers and from the fact that each flower lasts only one day.