Angiosperms

Angiosperms are considered to be the most recent and vigorous group of plants that have occurred on earth. There are more than 260,000 species of angiosperms in the world, belonging to over 400 families and 10,000 genera (such numbers may differ depending on the classification system used). Angiosperms occupy the majority of the terrestrial space on earth, and are the major components of the world's vegetation.

(1) Megadiversity of angiosperms in China

Brazil and Colombia, both located in the tropics, are considered to be countries with the most diverse angiosperms floras and which rank first and second. China, even though the main part of her land is not located in the tropics, the number of her angiosperms still occupies the third place in the world, and has approximately 300 families, 3, 100 genera and 30,000 species, accounting for 75%, 30% and 10%, respectively, of the total number of families, genera and species in the world. Among all the angiosperms in China, there are 60 families that contain 100 or more species (Table 1). The diversity of angiosperms in China is, perhaps, incomparable globally if we take into account not only species richness but also the diversity of ecological type's, species origin's, and their distribution characteristics.

Table 1 China's angiosperm families containing 100 or more species

No. of species	Family name
＞2,000	Compositae
1,500～2,000	Leguminosae
1,0000～1,500	Gramineae, Orchidaceae, Rosaceae
800～1,000	Labiatae, Ranunculaceae
500～800	Cyperaceae, Ericaceae, Scrophulariaceae, Umbelliferae
400～500	Cruciferae, Euphorbiaceae, Gentianaceae, Gesneriaceae, Lauraceae, Primulaceae,
	Rubiaceae, Saxifragaceae
300～400	Boraginaceae, Caryophyllaceae, Liliaceae, Salicaceae, Theaceae
200～300	Araceae, Asclepiadacaeae, Berberidaceae, Caprifoliaceae, Crassulaceae, Fagaceae, Fumariaceae, Polygonaceae, Urticaceae
100～200	Acanthaceae, Aceraceae, Amaryllidaceae, Annonaceae, Apocynaceae, Aquifoliaceae, Araliaceae, Balsaminaceae, Begoniaceae, Campanulaceae, Celastraceae, Chenopodiaceae, Convolvulaceae, Cucurbitaceae, Magnoliaceae, Melastomataceae, Moraceae, Myrsinaceae, Myrtaceae, Oleaceae, Rhamnaceae, Rutaceae, Solanaceae, Verbenaceae, Violaceae, Vitaceae, Zingiberaceae,

The multitude of mountain systems, criss-cross network of rivers, various climatic conditions and long geological history of China, along with the presence of the huge Qinghai-Tibetan Plateau (which has an average altitude of 4,500m), are determining factors responsible for the megadiversity of angiosperms in China. The diversity of angiosperms in China is characterized by three features:

a. The completeness of ecological types

Plants with various life forms, including arboreous trees, semi-arboreous trees (such as Haloxylon), shrubs, semi-shrubs (such as Calligonum), mini-semi-shrubs (such as Artemisia), to perennials and annuals, occur in China. Ecological types range from alpine tundra species (such as Dryas octopetala and Phyllodoce coerulea) to tropical rainforest elements; from super-xerophytic desert plants to mesic and hydrophylic species of moist lowlands; from cushion plants on the Qinghai-Tibetan Plateau, with high and cold, windy, environments; to mangroves along the tropical coastline of southern China. All have various representatives of angiosperms.

In China, different climatic zones are characterized by numerous, different, representative families and genera. For example, the Betulaceae and deciduous species of the genus Quercus (Fagaceae), the Salicaceae, Caprifoliaceae and Berberidaceae are representative of the temperate zone, while the Lauraceae, Magnoliaceae, Theaceae, Hamamelidaceae, Aquifoliaceae, Araliaceae, Nyssaceae and the evergreens trees of the Fagaceae, as well as monotypic Cercidiphylaceae and Tetracentraceae are typical of the subtropics. The most common angiosperm families in the tropics are the Dipterocarpaceae, Annonaceae, Burseraceae, Sapotaceae, Meliaceae, Guttiferae, Combretaceae, Samydaceae, Euphorbiaceae and Datiscaceae.

b. Abundant primitive and ancient elements

Many groups of angiosperms that are considered to be either primitive or of early genesis, occur in China, and some of them are only found here. Some species of Magnoliaceae, Ranuculaceae, Tetrecentraceae, Cercidiphyllaceae, Saururaceae, Chloranthaceae, Hamamelidaceae and Lardizabalaceae, have been the focus of world attention for their importance in studying the origin and phylogenetic development of angiosperms. In recent years, there have also been great accomplishments in paleobotanical research due, in part, to new discoveries of fossilized plants. These studies and findings are of theoretical importance for revealing the species diversity and the phylogenetic development of the angiosperms.

c. Richness of endemic taxa

The Chinese angiosperms have very diverse areal types among these, a large number are endemic. China has 246 endemic genera, and over 17,000 endemic species. Many of them are ancient relic and remnant types: Bretschneidera sinensis, Cercidiphyllum japonicum, Euptelea pleiospermum, Trochodendron aralioides, Shaniodendron subaequalum, Tetracentron sinensis, Helianthemum songoricum, Tetracena mongolica, Liriodendron chinensis and Davidia involucrata are examples of Chinese endemics. The researches made on these plants are of particular importance for understanding the phylogeny and historical processes of species formation of angiosperms in China as well as the world.

Endemic angiosperm genera and species in China are mainly distributed in the southeastern part of China, extending to the south of the Qinling-Dabie Shan Mountain line and to the east of Hengduan Shan Mountain. There are three centres of endemism with relatively concentrated distributions of endemic genera and species in this area. (1) East Sichuan-West Hubei-Northwest Hunan Centre. Almost all the woody genera of endemic angiosperms in this area are deciduous, arboraceous, trees and shrubs, and show evident signs of temperate elements. (2) West Sichuan-Northwest Yannan Centre, i. e., the southern section of Hengduan Shan Mountain. Herbaceous genera of this centre constitute a high proportion of the total genera in this region. Almost all of the woody genera of angiosperms here are deciduous arboraceous trees and shrubs. The striking and rapid uplifting of the Qinghai-Tibetan Plateau aided the formation of new endemic species, greatly enriching the diversity of angiosperms in China. (3) Southeast Yunnan-West Guangxi Centre. Because this centre is geographically located around the Tropic of Cancer, and in the transition zone between the Pan-Arctic and Neotropical Floristic Realms, most of its constituent families are tropical. About half of the endemic woody genera are evergreens, and all the endemic liana genera are woody plants.

(2) Threats to China's angiosperm diversity

China is the most populated country in the world, and has a long history of exploitation. The angiosperms are a prime target for exploitation and destruction mainly due to the ever-increasing human demand for timber, herbal medicines and cash. The distribution ranges of some species have been drastically reduced. and their wild resources greatly diminished. Examples include in the Orchidaceae, Cinnamomum spp., Phoebe spp., Paeonia, Coptis spp., Ferula spp., Fritillaria spp., Ormosia howii, Juglans mandshurica, Phellodendron amurense, Fraxinus mandshurica, Erythrophleum fordii, Burretiodendron hsienmu, Dalbergia odorifera, Madhuca pasquieri, Zelkova Schneideriana, Alseodaphne hainanensis, Hydnocarpa hainanensis, Garcinia paucinenvis, Panax ginseng, P. zingiberensis, P. stipuleanatus, Glycyrrhiza uralersis, Astragalus membranaceus, Dracaena cochinchinensis, Cistanche deserticola, Boschniakia rossica, Morinda officinalis, Oplopanax elatus, Acanthopanax senticosus and Rhodiola sacchalinensis. A preliminary estimate has revealed that 4,000 species of angiosperms suffer various kinds of threats. Among these, about 1,000 species have been listed as rare and endangered. The most extremely endangered species that have very narrow areals include Ormosia howii, Gleditsia japonica var. velutina, Acer yangjuechi, Betula halophila, Carpinus putoensis, Ostrya rehderana, Bhesa sinensis, Lumnitzera littorea, Hopea mollissima, Vatica guangxiensis, Tetrathyrium subcordatus, Manglietia decidua, Manglietiastrum sinicum, Parakmera omeiensis, Heteroplexis vernonioides, Populus pamirica, Nyssa yunnanensis, Archineottia gaudissartii, Diplandrochis sinica, Tangtsinia nanchuanica, Porolabium biporosum, Mussaenda anomala, Sonneratia hainanensis, Camellia granthamiana, Euryodendron excelsum, Apterosperma oblata, Eleutharrhena macrocarpa, Firmiana hainanensis and Otophora unilocularis and others. The angiosperm species that are either extinct or on the verge of extinction include Ombrocharis dulcis, Machilus minutiloba, Primula filchnerae, Ranalisma rostratum, Dracocephalum rigidulum, Craigia kwangsiensis and Epimedium simplicifolium.

(3) Strengthening the protection of angiosperms in China

Angiosperms are the most numerous macrophytes on earth, and are closely involved in the clothing, food, medicine and other raw materials of industries. The extinction of large numbers of angiosperms will undoubtedly threaten the survival of Man. We must, therefore, pay special attention to the conservation of angiosperms. In order to effectively preserve them, we must study the factors that have caused the species to become extinct, the degree of endangerment and the extinction processes, so as to work out appropriate preservation strategies. In this respect, the population viability analysis (PVA) and the determination of the minimum viable population size (MVP) are core research areas.

It is necessary that the presently protected areas be larger than those actually needed to sustain minimum viable populations because we are at present unable to conduct PVA’s on every species in any area. Once a species is lost, it will disappear forever!

Meanwhile, more attention should be paid to minimizing anthropogenic disturbances that can potentially drive species to become endangered and result in species extinctions. For example, preventing deforestation and the over-collecting of economically valuable species, establishing as more as possible protected areas and enhancing their management, preserving endangered species ex situ (change from wild to cultivated), are all effective in species conservation. All these methods should be guaranteed through legislative and policy measures. Only by doing so can the rich angiosperm resources of China be protected effectively. These not only contribute to the well being of the Chinese people, but also to the whole of mankind.