Some 3,700 plant species have been identified in the country, from which to date 23 have been declared natural monuments, 74 missing, 39 endangered, 171 vulnerable and 1,253 rare. The three major vegetation areas in Romania are the alpine zone, the forest zone and the steppe zone. The latter can be subdivided (depending on soil, climate, and altitude) into regions dominated by the Norway Spruce, European Beech, and various species of Oak, together with less widespread vegetation types such as the Dinaric calcareous block fir forest. The Danube Delta is the largest continuous marshland in Europe. Vegetation in the marshland is dominated by reeds, with Willow, Poplar, Alder, and Oak on the higher ground. The delta supports 1,688 different plant species.
There are almost 10,000 km2 (3,900 sq mi) (about 5% of the total area) of protected areas in Romania covering 13 national parks and three biosphere reserves: the Danube Delta, Retezat National Park, and Rodna National Park. The Danube Delta Reserve Biosphere is the largest and least damaged wetland complex in Europe, covering a total area of 5,800 km2 (2,200 sq mi). The significance of the biodiversity of the Danube Delta has been internationally recognised. It was declared a Biosphere Reserve in September 1990, a Ramsar site in May 1991, and over 50% of its area was placed on the World Heritage List in December 1991. Within its boundaries lies one of the most extensive reed bed systems in the world.