Through previous field research, a list and mapping of flora has been made, and the existence of 532 taxa (list of flora attached) has been established. According to the analysis of life forms, the flora of the Nature Park belongs to the Mediterranean area with the largest share of terophyta (41%) which survive the unfavorable season in the form of seeds. Evergreen forests of Aleppo pine and holm oak (as. Querco ilicis, Pinetum halepensis) have developed in the climatic conditions prevailing in this area. These communities are present in the area of Grpašćak – Stivanjska Gora – Mrzlovica and a number of other smaller locations. Systematic clearing, burning and grazing, and the use for firewood led to the fact that the holm oak forests have not been preserved, but degraded into maquis and garrigue (as. Cisto – ericetum arboreae). These communities of cistus and heather are most common in the area of Grpašćak, Priseka, and several other smaller locations. Cistus plants (the sticky Cistus monspeliensis, the hairy Cistus villosus, the white Cistus salvifolius) regularly grow in garrigues, and tree heath (Erica arborea) and strawberry tree(Arbutus unedo) are also very common. Shallower soils are covered in Aleppo pine (Pinus alepensis).
Rock land pastures of feather grass and sage (as. Stipo – salvietum officinalis brachypodietosum ramosi) dominated by butcher’s broom grass (Brachypodium ramosum), forming a thick carpet on the ground, are predominant in the southern part of Dugi Otok Island, Katina, Veli and Mali Buč, Gornja Aba, and most of the other islets of the Nature Park.
The abandoning of sheep breeding in recent decades is the cause of rock land pasture fouling by juniper (Juniperus oxycedrus). A mixture of feather grass and sage pastures with elements of pure Adriatic forests and maquis (as.Stipo – salvietum officinalis et Quercetum ilicis adria – provinciale) can be found on Koženjak, Brčasac, V. Dočić, in the Čelo – Ostrvica belt, and on Artak, while a mixture of feather grass and sage pastures with elements of pure Adriatic holm oak forests and maquis, stage mastic tree and myrtle (as.Stipo – salvietum officinalis et Quercetum ilicis adria – provinciale, stage Pistacia lentiscus – Myrtus communis) can be found on Katina Island. The endemic community of phalanga and Centaurea ragusina (as. Phalango – centauretumragusinae) developed on the bare gorge sections of rock along the southern coast to Cape Lopata, and in the canyon bay of Čuška Dumboka, as well as on Sestrice and Garmenjak in the sea splash zone.
The steep slopes of Telašćica are also the northernmost home of the tree spurge Euphorbia dendroides. It can also be found on Sestrica Vela Island in the community of Festuco-Koelerietum splendentis within the stands of feather grass and sage. The community of Statice cancellata (as. Plantagini – staticeum cancellatae) is represented in relatively small localities in the salination and sea splash zone, in a narrow coastal belt.
The flora of the Nature Park is rich in endemic plants. The most prominent of them is a subspecies of Croatian Centaury – Centaury of Dugi Otok (Centaurea ragusina ssp. lungensis) which grows only on Dugi Otok and on Kornati Islands. It is a strictly protected species, but because of the inaccessible rocks it grows on, it is not endangered by human activities.
An endemic species of Mid-Dalmatian woodroof (Asperula staliana) grows on the rocky shores and in garrigues. In late spring and summer, the rocky grasslands are full of Illyrian iris (Iris adriatica), and in August and September that same habitat is home of the endemic Seseli tomentosum. Rocky habitats with scarce soil are home of Dalmatian pyrethrum (Tanacetum cinerariifolium). The Adriatic swallow-wort (Vincetoxicum hirundinaria ssp. Adriaticum).can also be found here. The steep slopes are also home of silverbush (Convolvulus cneorum), a rare and relict species of Croatian flora, whose distribution range is completely overlapped with the distribution range of the Croatian Centaury, and the northernmost habitat of this species is a bushy steep slope inside the Nature Park. Among other endemic species that are Aurinia sinuata, Littoral Corydalis (Corydalis acaulis), Dalmatian clover (Trifolium dalmaticum) and 15 other species. Another significant part of the Nature Park’s flora are ten species of orchids which are strictly protected by law.
The species brought to this area by man include the Aleppo pine (Pinus alepensis), planted after World War II, which started spreading intensively from older plantations near Grpašćak towards Mir Bay and farther to the salt lake, and even to the southern parts of the island with plenty of cypress trees (Cupressus sempervirens) and rare stone pine (Pinus pinea).
Lately some invasive allochthonous species have been observed, and in the area of the Nature Park seven species with the status of invasive species have been recorded. None of the recorded invasive species within the area of the Nature Park has been spotted over larger areas and with a great density, but given their current distribution along frequent traffic roads and places of gathering of larger numbers of people, attention should be paid and the state of their populations should be monitored.