Angiosperms (angiosperms)

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) Use real flowers

A typical angiosperm flower consists of four parts: flower statue, 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) having pistils

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.

Double fertilization, that is, after two sperm cells enter the embryo sac, 1 combines with the egg cell to form a zygote, and the other 1 combines 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.

Sporophyte is highly developed

The sporophyte of angiosperms is more perfect and diverse 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 degenerates further (simplified)

The microspores (mononuclear pollen grains) of angiosperms develop Cheng Xiong gametophytes. Most mature male gametophytes have only two cells (2-nucleated pollen grains), of which 1 is vegetative cell and I is germ cell. A few plants divide 1 time to produce two sperm before pollination, so the male gametophyte of such plants is 3-nucleated pollen grains, such as Dianthus. The mature female gametophyte of angiosperms 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.

Characteristics of angiosperms

Angiosperms are the most advanced, diverse and widely distributed group in the plant kingdom. There are more than 1 10,000 genera and 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, which is the largest group of medicinal plants. The variety and wide adaptability of angiosperms are inseparable from the complexity and perfection of their structures, especially the characteristics of reproductive organs and reproductive processes, which endow them with internal conditions to adapt to and resist various adverse environments, so that they constantly produce new variations and new species in the contradictory struggle between survival competition and natural selection, and occupy an absolute advantage on the earth. Compared with gymnosperms, angiosperms have real flowers, so they are also called flowering plants; The ovule is wrapped in the ovary and is well protected. The fruit formed after fertilization of the ovary not only protects the seeds, but also helps them spread in various ways. The endosperm of double fertilization triploid is not a simple female gametophyte, but has the characteristics of parents, which makes the new plant have stronger vitality; Sporophytes are highly developed and further differentiated, and besides trees and shrubs, more are herbs; Anatomically, xylem has ducts, phloem has sieve tubes and companion cells, which makes the structure and physiological function of the conducting tissue more perfect. At the same time, in terms of chemical composition, angiosperms have been developing and complicated with the evolution of angiosperms, containing various natural compounds and having various physiological activities.

Classification of angiosperms

Angiosperms are divided into dicotyledonous and monocotyledonous, and their basic differences are as follows:

magnoliopsida

Root, taproot, fibrous root system

Stem vascular bundles are arranged in a ring, cambium vascular bundles are scattered, and cambium is absent.

Leaves with reticulate veins, veins flat or curved.

The radix of each part of the flower is 4 or 5, and the radix of each part is 3.

Pollen grains have three germination holes, and pollen grains have only one germination hole.

Embryo has 2 leaflets, 1 leaflet.

The above differences are not absolute, but actually overlap, such as hairy root plants such as Ranunculaceae, Plantago asiatica and Compositae in dicotyledonous plants; Plants with dispersed vascular bundles such as Zanthoxylum, Nymphaeaceae, Ranunculaceae and Dianthus; Flowers of Lauraceae, Magnoliaceae, Berberidaceae and Ranunculaceae have three cardinal numbers; Nymphaeaceae, Ranunculaceae, Polygonaceae, Papaveraceae and Umbelliferae all have L-shaped leaves. Among monocotyledonous plants, Araceae, Liliaceae, Dioscoreaceae and so on. There are reticular veins; 4 cardinal flowers such as POTAMOGETON, Liliaceae and Stemonaceae.

Magnolia

(1) Corbicula subfamily, Corbicula subfamily

Apocalyciflorus subclass is also called Archichlamydeae. Including tepals, simple tepals or types with calyx and corolla, petals are usually separated. Stamens and corollas are free. Embryo usually has a layer of integument.

A taxonomic catalogue of the engler system of Cleopatra.

(2) Cladosporium, a subclass of Taxodiaceae.

This subclass is also called Metachlamydeae, which mainly shows how many petals are connected to form a closed corolla. Corolla from radial symmetry to bilateral symmetry, forming various shapes, such as funnel-shaped, bell-shaped, lip-shaped, tubular, tongue-shaped and so on. The combination of various corollas increases the adaptability to insect pollination and the protection of stamens and pistils. Therefore, the sympodial flower groups have evolved more than the ectoplasmic flower groups.

Hua Lun number tends to decrease, from 5 rounds (calyx L, petal L, stamen 2 rounds, pistil carpel, such as Ericaceae, Persimmon, etc. ) to 4 rounds (calyx L, petals L, stamens L, carpels, such as Oleaceae, Caprifoliaceae, etc. ), and the number of whorls is gradually decreasing, for example, the number of stamens is the same as that of corolla lobes, such as

Usually there is no stipule, and the ovule has only one embryo cover.

A taxonomic catalogue of Schizophyllinae in Britain.

Monocotyledon class

Classification system of angiosperms

Since19th century, many plant taxonomists have made great efforts to establish a "natural" classification system. According to their respective phylogenetic theories, they put forward dozens of classification systems. However, due to the lack of understanding of the origin and evolution of angiosperms, especially the lack of fossil evidence, there is no relatively perfect classification system until now. At present, engler system and john hutchinson system are still widely used in the world. Cronquist system and Takhtar system are considered to be more reasonable in the arrangement of classification systems at all levels.

I. engler system

This is the system used by German taxonomists A. Engler and K. Pranti in their magnum opus Flora Naturalis 1897. It is the first complete system in the history of taxonomy, which divides the plant kingdom into 13 phylum, 13 phylum is seed phylum, and then divided into gymnosperms.

Engler's system put monocotyledonous plants before dicotyledonous plants, classified sympodial plants as a group of evolutionary plants, regarded catkin plants as the most primitive group of dicotyledonous plants, and regarded Magnoliaceae and Ranunculaceae as a more evolutionary group. These views are not recognized by many modern taxonomists.

Schigler system has been modified several times. In the twelfth edition of Flora published by 1964, dicotyledonous plants were placed before monocotyledonous plants. * * * 62 orders and 344 families, including 48 orders and 290 families of dicotyledons and 54 families of monocotyledons 14 orders. The revised Siegler system is adopted in the classification of angiosperms in medicinal botany textbooks, but some contents have changed.

Second, the john hutchinson system.

This system was established by British botanist J John J Hutchinson in his Flora I and II1926 and 1934. In the third edition revised by 1973, * * has 1 1 orders, 4 1 1 families, in which dicotyledonous plants belong to 82 orders, 342 families and monocotyledonous plants belong to 29 orders, 69 families.

John hutchinson thinks that Magnoliaceae and Ranunculaceae are the primitive groups of angiosperms, but he overemphasizes the two sources of woody plants and herbs, and thinks that woody plants are all evolved from Magnoliaceae and herbs are all evolved from Ranunculaceae, which makes some closely related families far apart in systematic position, such as Umbelliferae of herbaceous plants, Cornaceae of woody plants and Araliaceae. Herbaceous Labiatae and woody Verbenaceae are also opposed by most modern taxonomists.

Third, Tahiti system.

This is a system published by A. Takhtajan, a botanist in the former Soviet Union, in his book The Origin of Angiosperms 1954. He broke the traditional classification of dicotyledonous plants into two subcategories for the first time, namely, Schizophylla and Schizophylla. At the classification level, a "super-purpose" first-level classification unit is added. He separated Paeonia of Ranunculaceae into Paeoniaceae, which was consistent with the development of plant anatomy, palynology, plant cytotaxonomy and chemical taxonomy, and gained international recognition.

The Tahiti system has been revised many times. In the revised edition 1980, * * has 28 superfamilies, 92 orders and 4 16 families, including 20 superfamilies of dicotyledons (Magnoliaceae), 333 superfamilies of monocotyledons (Liliaceae), 7 1 order and 8 superfamilies.

Four, Cronquist system

This is the system in the book Classification and Evolution of Flowering Plants published by American botanist A. Cronquist in 1968. In the revised edition 198 1, * * has 83 orders and 388 families, including 64 orders of dicotyledons, 3 18 families of monocotyledons and 65 orders of monocotyledons.

Cronquist system is close to Tahiti system, and angiosperms (called Magnoliaceae) are divided into Magnoliaceae and Liliaceae, but the superfamily classification unit is cancelled, and the division of families is less than that of Tahiti system. Now some textbooks in our country adopt this system.

The two schools of systematic evolution have long been the focus of plant taxonomists to study the morphological characteristics of the oldest angiosperms, primitive groups and evolutionary groups, especially on the source of angiosperms' flowers, and they have the greatest disagreement, forming two schools, namely the so-called "fake flower school" and "true flower school", or "soft" school and "soft" school. The former is represented by German botanist engler, while the latter is represented by American botanists Bosch and Khalil and British botanist john hutchinson.

First, artificial flower school

It is considered that the flowers of angiosperms are exactly the same as those of gymnosperms, and each stamen and carpel is equivalent to 1 extremely degraded male flower and female flower respectively. Therefore, it is speculated that angiosperms originated from Ephedra curvata, a branch of Ephedra, as shown in the following figure. In this hypothesis, the bracts of male flowers become perianth and those of female flowers become carpels. After the bracts of each male flower disappear, only one stamen remains. Because gymnosperms, especially ephedra and lianas, are mainly unisexual flowers, it is speculated that primitive angiosperms have unisexual flowers. This theory is called artificial flower theory. Accordingly, the primitive groups of modern angiosperms should have unisexual flowers, flowerless perianth flowers, wind-blown flowers and woody soft flower inflorescences, such as Casuarina equisetifolia, pepper and willow. The view of this school is opposed by most modern systematics. According to the research data of anatomy and palynology, it is proved that catkin should be a secondary group.

Second, the true flower school

It is believed that the flowers of angiosperms evolved from the hermaphroditic bulbs of primitive gymnosperms, so it is speculated that angiosperms came from extinct cycads, especially cycads. In cycads, bracts on spore bulbs evolved into perianth, microspore leaves evolved into stamens, megaspore leaves evolved into pistils (carpels), and the axis of spore bulbs shortened into floral axis. This theory is called true perianth theory. Accordingly, modern angiosperms, especially many carpels of Magnoliaceae, are considered as the primitive groups of angiosperms.

gymnosperm

A lower class of gymnosperms. It has an archegonium, belongs to an archegonium plant, and is a seed plant that can produce seeds. However, their ovules are not covered by the ovary wall and do not bear fruit. Their seeds are naked, so they are called gymnosperms. 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.