| The Qinghai-Xizang (Tibet) Plateau, with a vast area above 4000m and the areas around drop drastically setting off the tremendous momentum, is one of the most extraordinary topographic and climatic features of the earth, and is often eulogized as the roof of the world and the third polar of the world. Although a fairly good account of the past floristic history of the Plateau is available, yet the knowledge of the flora of aquatic plants and aquatic vegetation is insufficient. During the period of 1999-2002, field expeditions and floristic collections of aquatic plants were carried out throughout the region. The results are mainly as follows:1.133 aquatic plant species and 5 infraspecific taxa (subspecies and variety) of 63 genera and 29 families of seed plants are known in the Qinghai-Xizang (Tibet) Plateau. Of them, 49 species, 1 subspecies and variety belong to 28 genera of 16 dicots families, and 84 species, 1 subspecies and 2 varieties belong to 36 genera of 13 monocots families. 12 species, 8 genera and 2 families are recorded for the first time in the Xizang (Tibet) Plateau.2. The newly recorded species are: Polygonum amphibium L. Myriophyllum sibiricum Kom., Nymphoides peltata (Gmel.) Kuntze, Menyanthes trifoliata L., Dopatrium junceum (Roxb.) Buch.-Ham. ex Benth., Utricularia intermedia Heyne, Sagittaria tengtsungensis H. Li, Potamogeton nodosus Poir., Blyxa echinosperma (Clarke) Hook,f, Monochoria vaginalis (Burm. f.) Presl ex Kunth, Spirodela polyrhiza (L.) Schleid., and Microcarpaea minima (Koen.) Merr.; the newly recorded genera are: Nymphoides (Gentianaceae), Menyanthes (Gentianaceae), Dopatrium (Scrophulariaceae), Microcarpaea (Scrophulariaceae), Sagittaria (Alismataceae), Blyxa (Hydrocharitaceae), Spirodela (Lemnaceae), and Monochoria (Pontederiaceae); and the newly recorded families are Alismataceae and Pontederiaceae.3. Referring to the delimitation of distribution patterns of seed plants in China, and in accordance with the analytic and comparative study of geographical elements, 136 aquatic plant species (excluding 2 cultivated species) occurring in the Qinghai-Xizang (Tibet) Plateau can be generalized as 12 geographical distribution patterns and 9 variants. Of them, 24 species have worldwide distribution pattern, 5 species (amounting to 4.5% of the total number of species, excluding the Cosmopolitan, the following is the same) have Pantropic distribution pattern, 5 species (4.5%) have Old World Tropicdistribution pattern and variant, 5 species (4.5%) have Tropical Asia and Tropical Australasia distribution pattern, 2 species (1.8%) have Tropical Asia to Tropical Africa distribution pattern, 8 species (7.2%) have Tropical Asia (Indo-Malaysia) distribution pattern and variant, 29 species (25.9%) have North Temperate distribution pattern and 2 variants, 17 species (15.2%) have Old World Temperate distribution pattern and variant, 18 species (16.1%) have Temperate Asia distribution pattern, 6 species (5.4%) have Central Asia distribution pattern and 2 variants, 5 species (4.5%) have East Asia distribution pattern and 2 variants, and 11 species (9.8%) are endemic to China.The distribution pattern of 62 genera containing aquatic plants in the Qinghai-Xizang (Tibet) Plateau can be generalized as 10 areal-types and 2 subtypes. Of them, 30 genera belong to Cosmopolitan, 5 genera belong to Pantropic distribution pattern, 3 genera belong to Old World Tropic distribution pattern, 2 genera belong to Tropical Asia and Tropical Australasia distribution pattern, 2 genera belong to Tropical Asia (Indo-Malaysia) distribution pattern, 14 genera belong to North temperate distribution pattern, 2 genera belong to East Asia and North America Disjuncted distribution pattern, 2 genera belong to Old World Temperate distribution pattern, 1 genus is an endemic to East Asia, and 1 genus is an endemic to China.Of the 29 families containing aquatic plants in the Qinghai-Xizang (Tibet) Plat...
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