Quercus protoroburoides

Quercus protoroburoides, the Rila oak (Bulgarian: рилски дъб), is a deciduous species of oak endemic to the Rila Mountains of southwestern Bulgaria. Within Rila, the species is distributed only in five localities on steep, rocky south-facing slopes of the Rilska River valley, at the tree line between 1,500 to 1,750 metres (4,920 to 5,740 feet) above sea level. The Rila oak was first discovered in 1968 and officially accepted as a distinct species in 2017.

Quercus protoroburoides grows scattered or in small groups, higher than the local sessile oak (Quercus petraea) or fir-beech forests. In terms of morphology, it most closely resembles the Strandzha oak (Quercus hartwissiana) and the sessile oak, but it has a specific leaf epidermis and a very distinct distribution. Trunk diameter ranges from 30 to 100 cm (12 to 39 in) and the tree height reaches over 20 m (66 ft) in favourable locations.

The Rila oak forests are listed in the Red Data Book of the Republic of Bulgaria as a critically endangered habitat. The species is protected as part of the Rila Monastery Nature Park and its subordinate nature reserve Rila Monastery Forest.