The entire ANP territory belongs to the montane – subalpine zone, and the species that compose the vegetation are characteristic to the mountain habitat.

The vegetation is structured by altitude as follows: mountain meadows, spruce forests (Picea abies) and deciduous forests, where one can encounter species such as: beech (Fagus silvatica), hornbeam (Carpinus betulus), Sycamore maple (Acer pseudoplatanus), Wych elm (Ulmus montana), ash (Fraxinus excelsior), wild cherry (Cerasus avium), field maple (Acer campestre), White birch (Betula verrucosa), rowan (Sorbus aucuparia), goat willow (Salix caprea), black walnut (Juglans regia) etc.

Due to the local conditions of soil, climate and topography, this natural framework includes some changes, perturbations and inversions.

Mountain forests are well developed in the upper part of the valleys, between altitudes of 1,200 and 1,600 m. At this level the most encountered trees are the spruce (Picea abies), silver fir (Abies alba) and, rarely, larch (Larix decidua) and yew (Taxus baccata).

As a feature of the karst plateaus of the Apuseni, resulting from thermal inversions, there are some areas where the coniferous zone had disappeared entire and is replaced by beech (Fagus silvatica) forests, which are next to mountain meadows.

The limit between the deciduous and coniferous forests is situated between altitudes of 600-1,300 m, depending on the relief, substrate and microclimate, which sometimes also lead to vegetation inversions.

Limestone areas represent a special landscape, different from the plateaus and rocky areas. The limestone plateaus of Batrana, Padis, Ocoale, Marsoaia and Ursoaia, are mostly unforested due to the lack of water, which lead to the presence of mountain meadows, whose presence cannot be explained only by the altitude factor. In these mountain meadows some special plant associations can also be found. The mountain meadows of the karst plateaus are more developed in the central depression areas, while the edges of the plateaus are almost always covered by forests. Today they replace the old beech woods cleared in the past and they belong to the fescue (Festuca) formation with different species. Due to the thermal inversions within these closed depressions, the spruce appears in the central part of the depression, while the deciduous forests grow on the nearby peaks, a perfect example being the Padis Basin.

These mountain meadows are characterised by a very high biodiversity, between 1995 and 2000 420 species of plants were identified.

Due to some special microclimate conditions, a type of northland vegetation grows on unusual southern latitudes, together with some alpine species that grow here, also on an unusually low altitude. Inside in the lower part of large dolines, the beginning of the vegetative season is delayed due to the thermic stratification of the air. At the entrances of caves, vegetation typical for shadowed and moist areas is found.

A special type of vegetation is encountered in wetlands areas along rivers. Wood species characteristic to riparian areas are: willows (Salix alba, Salix purpurea, Salix triandra), black poplar (Populus nigra), alder (Alnus glutinosa), and, of the herbs, sedges (Carex sp.), iris (Iris pseudaccorus), etc. This riparian vegetation is found mostly along Aries Mare river.

Depending also on the presence of water there are peat bogs at high altitudes, especially in spruce forests. These bogs are formed either on a siliceous substrate in almost horizontal areas (Molhasurile de la Izbuce), or in karst areas where the bottom of the dolines got an silt waterproof coat (Padis, Barsa, Onceasa).  

The flora of these peatbogs is composed of oligotrophic plants with a slow growth, but especially with moss species of Sphagnum, which by its way of life influences the reaction, chemistry, feature and generally the life conditions of oligotrophic peatbogs. The moss that constitutes the base of the entire flora is quickly growing in small pillows, and mainly composed of Sphagnum species. These small pillows are overgrown by Vaccinum microcarpum, Drosera rotundifolia, Andromeda polifolia, Carex pauciflora, Eriophorum vaginatum, Scheuchzeria palustris, Carex limosa, Carex rostrata etc. On the surface of these petbogs very interesting plant associations were described. The plant formations analysed in 1987 by Pop and his co-workers were placed in the following plant associations: Eriophoro vaginato-Sphagnetum (which generated especially by their agents the largest amount of peat), Caricetum limosae, Rhynchosporetum albae, Vaccinio – Pinetum mugi, Carici rostratae – Sphagnetum and Carici stellulatae – Sphagnetum (transitional plant associations to mesotrophic marshes developed at the edge of the petbogs).

Mugo pine (Pinus mugo) is present (in a few patches) in the peatbogs of Izbuce; this location is considered as the lowest altitude within the Apuseni mountains (Pop 1939). By their floral composition the pine patches from the south-eastern part of larger peatbog resemble a lot with those of the Tatra mountains (Hadac1969, ap. Pop et. al, 1987), from which they differer by the abundance/dominance of Sphagnum species and by their more hydrophilous character (37.5%), and the strong infiltration of acidophile species (25%). Due to the above-mentioned ideas, Pop and his co-workers (1987) placed these pines into a new category –sphagnetosum of the Vaccinio -Pinetum mugi association.

The following lines briefly present from an ecologic and floral point of view the main plant associations that define the territory of ANP (***, 1992):

Sedo hispanici – Poetum nemoralis: It is encountered on shadowed limestone rocks, from the nemoral forest level on Sighistel, Boga and Galbena valleys, and Ordancusa gorge.

Thymetum comosi: This pioneer endemic cenosis identified by Thymus comosus is growing on fine and coarse screes at the base of limestone rocks of Ordancusa gorge.

Parietarietum offcinalis: It is growing on shadowed or semi-shadowed screes at the base of limestone rocks in the park (ex: Galbena gorge).

Scorzonero roseae-Festucetum nigricantis: These meadows are frequently encountered on the upper mountaineous and sub-alpine levels (Micau, Piatra Graitoare, Carligate).

Violo declinate – Nardetum: This association is frequently found on the mountain and sub-alpine level where the soil is poorer than in the above-mentioned case.

Seslerietum rigidae: This association is frequently encountered in ANP on shadowed or semi-shadowed rocks from the mountain level (Somesul Cald gorge, Piatra Bulzului, Boga valley, Ordancusa gorge).

Epilobio – Juncetum effusi: These hygrophileous plant formations identified by Juncus effusus, grow on riparian areas and valleys (Calineasa valley, Poiana Horea), on alluvial soils with a poor mineral content.

Festuco-Agrostetum capilaris: These mesophillic meadows are extended throughout the entire park, up to upper limit of the beech forest (Sighistelul and Bulz valleys, Micau, Ordancusa gorge, Galbenei valley).

Caricetum limosae: This rare association which presents a special phytogeographic interest has been described for oligotrophic mountains bogs in the park. Along with it, we can also find the Sphagno-Rhyncosporetum albae association.

Junco – Caricetum fuscae, Sphagnetum magellanici and Carici flavae - Eriophoretum latifolii are found in eumesotrophic mountain bogs from Calineasa valley, Padis Plateau, Molhasurile de la Izbuce and Sighistel valley.

Calamagrosti – Digitalietum: They are found on deforested lands at the beech level and in mixed forests of beech and spruce of Sighistel and Galbenei valleys, and on Garligati Mountain.

Carpino fagetum: These forests are sporadically spread on Sighistel, Galbenei and Albacul valleys. They verge at the base of shadowed and semi-shadowed mountain sides at the lower mountain level.

Symphyto-Fagetum: These pure beech woods are frequently encountered all over Apunseni Nature Park between 600 and 1,100 m (Boga, Galbenei and Garda valleys, Somesul Cald gorge).

Leucanthemo waldsteinii –Fagetum (Ordancusa gorge, Alcaului and Garda valleys).

Hieracio rotundati – Piceetum: These widely extended forests (Calineasa, Padis, Micau, Ordancusa and Somesul Cald gorges) form the spruce zone.

Campanulo-Juniperetum: These sub-alpine shrubs of small juniper are sporadically met on the entire northern crest of the park between Poienii and Dealul Paltinisului Peaks, being quartered in glades and clearings of the upper spruce zone (1,400-1,600m).

Out of the taxa given in the National Red List (Oltean et al. 1994), examples identified in peatbogs of ANP are: Andromeda polifolia, Campanula patula ssp. abietina, Carex limosa, Carex strigosa, Dactylorhiza maculata s. l., Drosera rotundifolia, Empetrum nigrum ssp. nigrum, Leucanthemum waldsteinii, Listera cordata, Menyanthes trifoliata, Pedicularis limnogena, Rhynchospora alba, Scheuchzeria palustris, Swertia perennis, Vaccinium microcarpum, Vaccinium oxycoccos, Valeriana dioica subsp. simplicifolia.

Due to the specific conditions within different ANP ecosystems, a number of endemic species has been identified, such as: Transylvanian lilac (Syringa josikaea) (Stefan (1971), sconite (Aconitum calibrotryon ssp. skarisorensis), pink (Dianthus julii wolfii), violet (Viola josi), many types of the hawkweed (Hieracium bifidum ssp. biharicum, H. sparsum ssp. prophirictum, H. kotschyanum etc.), Edraianthus kitaibelii, a plant found here for the first time, and Melampyrum bihariense.