1, a subclass of gymnosperms. It has an archegonium, which is not only an archegonium plant, but also a seed plant that can produce seeds. They are called gymnosperms because their ovules have no ovary wall and no pericarp, and their seeds are naked. Sporophyte is a plant, extremely developed, mostly trees, a few shrubs or vines (such as tropical vines), usually evergreen, with needle-shaped, linear and scaly leaves, and few flat broad leaves (such as bamboo and cypress). Most secondary xylem only has tracheids, and a few have vessels (such as ephedra). There are only sieve cells in phloem, but no companion cells and sieve tubes. Most female gametophytes have archegonia, and a few kinds of sperm have flagella (such as cycads and ginkgo biloba). Gymnosperms appeared in Paleozoic, flourished in Mesozoic, and gradually declined due to geological and historical changes. There are about 800 species of modern gymnosperms, belonging to 5 classes, 9 orders, 12 families and 7 1 genus. There are 5 classes, 8 orders 1 1 family 4 1 genus 236 species and some varieties and cultivated species in China. Many gymnosperms are important trees, especially in the northern hemisphere. More than 80% of large forests are gymnosperms, such as larch, fir, Pinus armandii, spruce and so on. All kinds of wood are light, strong, inflexible and elastic, and are good materials for buildings, vehicles, ships and paper making. Cycas leaves and seeds, ginkgo seeds, pine pollen, pine needles, pine oil, ephedra and arborvitae seeds can all be used as medicine. Tannin, volatile oil, resin and rosin can be extracted from various barks and trunks such as larch and spruce. The young leaves of Cycas spinosa are edible and the pith can be used to make sago. Seeds of Ginkgo biloba, Pinus armandii, Pinus koraiensis and Torreya grandis are edible dried fruits. Gymnosperms are primitive seed plants with a long history of occurrence and development. The earliest gymnosperms appeared in Paleozoic, and they were the main plants in all continents from Mesozoic to Cenozoic. There are many kinds of gymnosperms in modern times, which appeared in the tertiary period, and then survived the ice age and have been propagated to this day. According to statistics, there are about 850 species of gymnosperms in the world, belonging to 79 genera 15 families. Although the number of species accounts for only 0.36% of angiosperms, they are distributed all over the world, especially in the cold temperate zone of the northern hemisphere and the subtropical Zhongshan-alpine zone, often forming a large area of coniferous forests. (1) Diversity of gymnosperms in China China has a vast territory and complex climate and landform types. From Mesozoic to Cenozoic Tertiary, it has been a warm climate, and the Quaternary Ice Age was not directly damaged by the northern continental ice sheet, which basically maintained a relatively stable climate since Tertiary, resulting in the characteristics of rich species, ancient origins, many ancient remains, many endemic components and diverse types of coniferous forests in China. According to statistics, there are about 250 species of gymnosperms 10 family, 34 genera in China, accounting for 66.6%, 4 1.5% and 29.4% of the total families, genera and species of gymnosperms in the world, respectively, making China the richest country in gymnosperms in the world. Many gymnosperms in China are ancient remnants or relict species that have long been extinct in other parts of the northern hemisphere, and they are often unique monotypic or oligotypic genera. For example, the unique haplotype family-Ginkgo biloba; The endemic monotypic genera are Metasequoia, Metasequoia, Cryptomeria, Dictyophora and Dictyophora. Semi-endemic monotypic and oligotypic genera include Taiwania, Cunninghamia lanceolata, Fokienia, Platycladus orientalis, Taxodium, Taxodium, Cycas and other remaining species. And fir. Although gymnosperms account for only 0.8% of angiosperm species in China, the area of coniferous forest formed by them is slightly higher than that of broad-leaved forest, accounting for about 52% of the total forest area. There are few gymnosperms in coniferous forests in Northeast China, North China and Northwest China, but there are abundant gymnosperms in coniferous forests in Southwest China. In South China, Central China and East China, in addition to primary coniferous forests, large-scale artificial Chinese fir forests, Pinus massoniana forests and cypress forests are more common. (2) Threats and protection of gymnosperms in China Although there are abundant gymnosperms and forest resources in China, most gymnosperms have straight trunks, excellent materials and high timber output, so the coniferous forests formed by them are often regarded as the priority targets of logging and are being threatened and destroyed by strong human activities. For example, in 1950s, the natural forests in Daxing 'anling, Xiaoxing 'anling and Changbai Mountain, the largest coniferous forest areas in China, were developed and utilized to varying degrees, while in 1960s and 1970s, the natural forests in Hengduan Mountain, another large coniferous forest area, were intensively cut down one after another, leaving only inaccessible mountains, deep slopes of river valleys and natural coniferous forests in nature reserves. In Central China, East China and South China, due to the demand of population density and economic development, all kinds of natural coniferous forests in Zhongshan are mostly cut down and replaced by artificial Pinus massoniana forest, Chinese fir forest and cypress forest. With the cutting and destruction of various natural coniferous forests, the original ecological environment has been changed, and the disappearance and endangerment of undergrowth creatures have been accelerated. At the same time, gymnosperms with important ornamental value and economic value have also been seriously damaged, such as Cycas Panzhihua, Cycas Guizhou, Cycas polymorpha (Cycas multiforme) and Cycas branchii (Cycas Michaelis), which have been seriously damaged after new distribution points have been published or discovered. Cephalotaxus fortunei and Taxus cuspidata were new anticancer medicinal plants discovered in 1960s, 1980s and early 1990s, and then they were cut down on a large scale and their resources were drastically reduced. It is preliminarily found that the gymnosperms in Baisuchuan, Admiralty are extinct gymnosperms in China, which have been rediscovered but not extinct. The wild extinct species with only cultivated plants and no wild plants are Cycas, Cycas Taiwan and Cycas Sichuan. The extremely endangered species with very narrow distribution area and few plants are: Cycas multifida, Cycas tomentosa, Cycas Changbai, Cycas hainanensis, Abies baishanzu, Picea yuanbaoshanensis, Picea albiflora, Sequoia Taibai, Tsuga brevifolia, Pinus Long Lin, Cephalotaxus gongshanensis, Cephalotaxus Taiwan Province and Cunninghamia yunnanensis. There are about 63 endangered and threatened gymnosperms, accounting for about 28% of the species, among which Abies baishanzu and Abies formosana are listed as the most endangered plants in the world (table 1). 2. Angiosperms Angiosperms are a kind of seed plants. Angiosperms or flowering plants are the last plant species to appear in the evolutionary stage. They first appeared in the early Cretaceous and occupied most of the world's plant kingdom in the late Cretaceous. The seeds of angiosperms are hidden in nutritious fruits, which provides a good environment for life development. Fertilization can be carried out by wind, mostly by insects or other animals, so that flowering plants can spread widely. Angiosperms are the highest class in the plant kingdom, and have occupied an absolute advantage on the earth since Cenozoic. At present, there are more than 200,000 species of angiosperms, accounting for half of the plant kingdom. There are more than 2,700 genera and about 30,000 species in China. There are so many kinds of angiosperms and so wide adaptability, which are inseparable from their complex structure and perfection. In particular, the structure of reproductive organs and the characteristics of reproductive process provide it with internal conditions to adapt to and resist various environments, so that it constantly produces new mutations and new species in the process of contradictory struggle between survival competition and natural selection. The following five evolutionary characteristics of angiosperms are compared with gymnosperms. As for the characteristics of seed plants that can produce seeds, transport sperm by pollen tubes and have endosperm, I won't go into details here. (1) A typical angiosperm flower with true flowers consists of four parts: calyx, corolla, stamen group and pistil group, and each part is called flower part. There are extremely diverse changes in the number and morphology of each part of angiosperm flowers, which are produced by natural selection, preservation and continuous strengthening in the process of evolution, adapting to the conditions of insect-borne, wind-borne, bird-borne or water-borne pollination. (2) Pistil consists of carpels, including ovary, style and stigma. The ovule is enclosed in the ovary and protected by the ovary, thus avoiding insect bites and water loss. After fertilization, the ovary develops and bears fruit. Fruits have different colors, smells and tastes, and there are many ways of cracking. The pericarp often has various hooks, thorns, wings and hairs. All these characteristics of fruit play an important role in protecting seed maturity and helping seed spread, and its evolutionary significance is self-evident. (3) Double fertilization exists, that is, after two sperm cells enter the embryo sac, 1 will combine with the egg to form a zygote, and the other 1 will combine with two polar nuclei to form 3n chromosomes and develop into endosperm. Young embryos feed on the endosperm of 3n chromosome, which increases the contradiction in new plants and thus has stronger vitality. All angiosperms have double fertilization, which is also evidence that they have the same ancestor. (4) The sporophyte of angiosperms is highly developed, which is more perfect and diversified than other plants in morphology, structure and life form. There are the tallest trees in the world, such as eucalyptus almond, which is as high as 156 meters; There are also grasses as thin as sand, such as rootless duckweed. ], each square meter of water surface can accommodate 3 million individuals, the fruit weighs 25 kilograms, and only contains 65,438+0 seeds, such as Royal Palm [Royal Palm (H.B.K.) O.F. Cook]; There are also plants as light as dust, with 50,000 seeds weighing only 0. 1 g, such as some epiphytes in the tropical rain forest; Plants with a life span of 6000 years, such as Dracaena; There are also plants (such as some cruciferous plants growing in the desert) that bloom and bear seeds within 3 weeks to complete their life cycle; There are aquatic, sandy, stony and saline-alkali plants; There are autotrophs, saprophytes and parasitic plants. Anatomically, angiosperms have vessels in the secondary xylem and companion cells in the phloem. Gymnosperms are generally tracheids (except Ephedra and Hemerocallis), and there are no associated cells in phloem. The perfection of transportation organization makes the material transportation in the body smooth and the adaptability enhanced. (5) The gametophyte further degenerates (simplifies) the microspores (mononuclear pollen grains) of angiosperms and develops into male gametophytes. Most mature male gametophytes have only two cells (two nuclear pollen grains), of which 65,438+0 are vegetative cells and I is germ cells. A few plants divide 65,438+0 times before pollination to produce two sperm, so the mature female gametophyte of angiosperms of this kind of plants is called embryo sac. Usually, embryo sac has only 8 cells: 3 antipodal cells, 2 polar nuclei, 2 helper cells and 1 egg. Antipodocytes are the remnants of the vegetative part of prothallus. Some plants (such as bamboo) have more than 300 antipodal cells, while others (such as apples and pears) disappear when the embryo sac matures. Helpers and eggs are called oogonia, which are the remnants of the archegonium. It can be seen that the male and female gametophytes of angiosperms have no independent living ability and are parasitic on sporophytes all their lives, which is more simplified in structure than gymnosperms. The simplification of gametophyte is of evolutionary significance in biology. The above characteristics of angiosperms make them superior to other plants in the competition for survival. With the appearance of angiosperms, the scene of bright colors, various kinds and rich flowers and fruits appeared for the first time on earth. With the development of angiosperm flower morphology and the storage of high-energy products in fruits and seeds, the animal kingdom (especially insects, birds and mammals) that directly or indirectly depend on plants for their livelihood has also developed and prospered rapidly. Angiosperms are divided into two categories-dicotyledonous plants (Magnoliaceae) and monocotyledonous plants (Liliaceae). The Latin name of angiosperms comes from Greek compound words. Angio—-coated and-spermseeds, together, the first case of the plural is angiosperm, and the English name is angiospunor. 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.