Rhododendron macgregoriae is a rhododendron species native to Indonesia and Papua New Guinea at altitudes of . It is an evergreen shrub or tree purportedly growing to in height, with leaves that are ovate-elliptic or obovate-elliptic, 40–140 × 25–50 mm in size. The 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.
References
J. Bot. 29: 177 1891. The Plant List Vireya.net article Hirsutum.com Encyclopedia of Life