Rhododendron macgregoriae is a rhododendron species native to Indonesia and Papua New Guinea at altitudes of 500 to 3350 m. It is a shrub or small tree that grows to 15 m in height, with leaves that are ovate-elliptic or obovate-elliptic, 40–140 × 25–50 mm in size. Flowers are light yellow to orange. R. macgregoriae is relatively easy to grow in cultivation and a popular parent for hybrid cultivars. Today, nearly one hundred named cultivars are of "mac" descent.