The flora of The Nature Park Rila Monastery is unique and features a multitude of protected relict and endemic species. The biological diversity of this flora is great and expressed by many species of the following floral groups: freshwater aquatics, fungi, lichens, mosses, ferns, gymnospermous and angiospermous plants.
At the high alpine elevations of the park the Icelandic Lichen (a protected species) occupies broad swaths of territory.
There are 162 species of fungi that occur in the park. 16 of these fungal species have some level of conservation status: 9 are included in The European Red List of Rare, Threatened and Endangered Species and 1 in listed in The Bern Convention.
Widely distributed throughout the park are approximately 150 species and subspecies of moss, several of which are protected species.
The park’s character is strongly influenced by the presence of gymnospermous higher plants.
There are impressive stand of the following tree species: Beech (Fagus sylvatica), Winter Oak (Quercus petraea), Spruce (Picea abies), Fir (Abies alba), White Fir (Pinus peuce), Maple (Acer campestre), Sycamore (Acer pseudoplatanus), Birch (Betula pendula), and others.
Especially valuable in terms of biodiversity are several individual specimens of the following woody species: (Taxus baccata), Boris Fir (Abies boris regisi), Rila Oak (Quercus protoruburoides), and (Ostrya carpinifolia).
At elevations few other woody species can tolerate, Dwarf Pine (Pinus mugo) is found in vast stands. The biomass of just this species represents 17% of the total biomass of all coniferous tree species within the park.
The biodiversity of the park’s angiospermous plant species is rich. There are 1,400 such floral species; this figure represents 38% of all angiospermous species in Bulgaria. Among this multitude of species there are a number of especially valuable endemics whose populations are restricted to the park’s territory and are well preserved. The following are the most interesting of these endemics: Primula deorum, Rheum rhaponticum, Anthemis sanctijohannis, Ligularia gluca, Verbascum jankaeanum, and Geum bulgaricum.
Of all floral species within the park, about 100 receive some form of conservation status. The best preserved communities among these 100 protected species are found at the high alpine zone.