Angiosperms are the most advanced, diverse, widely distributed and adaptable groups in the plant kingdom. In different systems, angiosperms have more than 300 to 400 families, 1 10,000 genera and 200,000 to 250,000 species. More than half of the total species in the plant kingdom. They are distributed in different climatic zones. Because of the high temperature and abundant rain, the tropics and subtropics are the most abundant. There are about 40,000 species in the Amazon region of South America. There are 20,000-30,000 species in other tropical regions. In temperate regions, due to low temperature and less rainfall, species are gradually decreasing. Judging from the situation in China, Yunnan Province has a good climate with more than 10,000 species of plants, while Hebei Province is located between 26 and 43 degrees north latitude. Relative species have decreased a lot, about 2500 species. The arctic has been greatly reduced, and there are almost no angiosperms in many places, and only a few species survive tenaciously in a few places. For example, the distribution latitudes of Salix pubescens and long-rooted opium poppy are all above 80 degrees. Near Jenny Island in Morgit Bay, Antarctic continent in the southern hemisphere, there is a Dianthus species-Dianthus crassifolia. In addition, from the altitude point of view, the higher the terrain, the lower the temperature, about every rise 100 meters, the temperature drops by 0.5℃, and the composition of plant species also changes; In the Everest region, the climate is very cold, and only a few hardy species can survive. There are also Stellaria in the area of 5000-5500 meters. Snow lotus is also distributed in the heights of Tianshan Mountain in Xinjiang.

Extreme natural environment and desert. For example, in the desert area of Xinjiang province, there are Populus euphratica and Haloxylon ammodendron, which can adapt to the arid climate. It seldom rains in the Sahara desert of North Africa, and it doesn't rain in some places for more than ten years. There is a kind of plant called small tooth grass. Because of extreme drought, its life cycle is very short, only a few days, so it is called short-lived plant. With a little rain, it can germinate, grow, blossom and bear fruit, and complete the task of a generation. Flowers will bloom when it is slightly wet at ordinary times. Once dried, the flowers will close, which is very sensitive. In the desert areas of the United States and Mexico, there is a special plant that adapts to drought, that is, succulents, that is, the famous cactus family. The whole body is prickly, the leaves are degraded, and the stems are mostly used for drought resistance. Some of them are shaped like giants. If you cut them open with a knife, they can drink water directly. On saline-alkali land, there are angiosperms with strong salt tolerance, among which Oryzaceae is the most famous. For example, Salicornia is a kind of panicum miliaceum, which has much meat and small leaves. The stems are nodal and can be used for photosynthesis. On the cross section of the stem, there are obvious characteristics: the epidermis is thin and smooth, the palisade tissue has two layers, the internal cells are large and watery, and the vascular tissue is in the center. Hydrophilicity is formed under the influence of sodium ions. More than 92% of the biomass of Salicornia halophila is water. After burning, dried Salicornia angustifolia leaves a lot of ash, accounting for more than 45% of the dry weight. The above stem structure, high water content and high ash content are typical characteristics of halophytes. Salicornia bigelovii Torr was born on the salt marsh, which contains the most salt and can be regarded as its standard representative. The evolution of halophytes in rice family is carried out under the condition of salt evolution.