Compositae is a relatively young and highly evolved family. Although it appeared late on the earth, due to its advanced morphological structure and strong adaptability to the environment, this young family jumped to the top of the world's seed plants in a relatively short period of time, both in species number and distribution range. Many experts in plant taxonomy and systematic evolution agree that it has reached the highest stage of systematic evolution of angiosperms (especially dicotyledons).
Most species of Compositae are herbaceous, and a few are woody, accounting for only 1.5% of the total number of undergraduate plants. From the evolutionary point of view, herbaceous plants spend the bad period of environment with seeds or underground organs (roots, rhizomes, tubers, bulbs, etc.). ) is more adaptable than woody plants, so its evolutionary degree is higher than woody plants. Except for a few species of compositae (such as zinnia, Bidens bipinnata), which are opposite leaves, most of them are alternate simple leaves.
1. The reproductive organs of compositae plants are characterized by flower heads.
The flower head consists of many sessile florets (or only one flower) densely growing at the top of the inflorescence axis and gathering into a head shape. It looks like a big flower, but it is actually an inflorescence composed of many flowers (or a flower). Generally, it consists of many flower heads, such as panicles and corymbs. Rhapotheca's head is very small, containing only one flower, and many small heads form a larger compound head.
The outermost flower head is covered with involucre, which is generally green and leaflike. Its function is undoubtedly to protect the flower head before it opens. However, the involucre of many genera and species in undergraduate course is specialized into organs with special purposes, such as the involucre of helichrysum becomes membrane-like and brightly colored to attract insects; The involucre of Arctium lappa, Atractylodes lancea and Xanthium sibiricum. The involucre of sessile chrysanthemum and Smilax China has sticky glandular hairs, which can be used for animals to sow fruits and seeds.
Many small flowers merge into a head shape, which makes every small flower that is not obvious at first gather together, making it bigger and more eye-catching, especially when the tongue-shaped flowers at the edge of inflorescences of some genera and species open, making the inflorescences bigger and more eye-catching, which is beneficial to attracting more insects.
In the flower heads of some genera and species, there is a clear division of labor between florets, such as sunflower. Tongue-shaped flowers at the edge of inflorescence are asexual flowers, which can not bear fruit, while tubular flowers in the middle can produce pollen and bear fruit, which are bisexual flowers. Different from marigold, the tongue-shaped flowers on the edge are female flowers that can bear fruit, while the tubular flowers in the middle are male flowers that can only produce pollen but cannot bear fruit.
2. The structure of each flower on the head inflorescence can be summarized as follows: sepals become crown hairs, five petals are United, stamens are aggregated, and ovary 2 carpels are in the lower position. However, there are great differences between genera and species, and simplification or specialization is common.
Sepals: Sepals are protective organs, especially in bud stage. The flower head of Compositae is protected by involucre, so the sepals have lost their original functions. Some species specialize into prickly, hairy or flaky "crown hairs" at the top of the fruit, which become the sowing organs of fruit seeds, such as dandelion and crow onion, which can make the fruit fly everywhere with the wind. Another example is Bidens bipinnata, whose crown hair becomes prickly, which can make the fruit adhere to the animal's body and spread.
Petals: 5 pieces, connected with each other to form a tube or tongue. From the evolutionary point of view, closed flower is a late-developing trait, which is more evolutionary than open flower. If the base of the petals is connected into a long tube, and the five petals at the top are arranged radially and symmetrically, it is called a tubular flower, such as the small flower in the center of the sunflower inflorescence. If the petals are connected into a short tube at the base, and five petals are connected into a piece, the two sides are symmetrical and extend to one side, it is called a tongue-shaped flower, and there are five teeth at the top of the petals, which means that the tongue-shaped flower is formed by connecting five petals together. Such as dandelion flowers. In some species, the base of petals is connected into a long tube, but five petals form a lip shape, which is divided into upper and lower lips. Sometimes only one lip develops and the other lip degenerates, forming false tongue-shaped flowers, such as small flowers outside the inflorescence of marigold and sunflower. At the base of corolla tube, there are annular nectaries, which can secrete nectar and store it at the base of the tube.
Stamens: 5. Filaments are separated from each other and anther edges are connected with each other to form a hollow tube, that is, a polyandry stamen. Whenever the anther matures, pollen grains are scattered in the "tube" of the stamen of a polyandry, and are "pushed out" of the tube when the pistil style grows. Some kinds of anther bases are specialized in the shape of "tail" to protect nectar and nectar at the base of petal tube from dust or rain. At the top of each anther, there is a prominent "anther septum". When the stamens are immature, the five anthers abut against each other to form a "cover" to seal the mouth of the anther tube and play a protective role.
Pistil: The ovary is in the lower position, consisting of two carpels, one locule and one inverted ovule, and the base is attached. There is a style that extends into the anther tube, and the top stigma is 2-lobed, but the stigma is not open when the pistil is immature. In the upper part of the style, there is often a circle of hair called "sweeping pollen". Whenever the style develops and elongates, this kind of "sweeping powder" can "push out" the pollen grains scattered in the anther tube, which is convenient for flower-visiting insects to carry. Flowers of compositae usually have stamens that mature first. After the pollen grains are pushed out during the style elongation, the top stigma opens again to receive pollen from other flowers. This is an adaptation to avoid self-pollination. However, once the stigma fails to receive pollen from other flowers, that is, cross-pollination fails, the stigma can bend down, touch the "pollination surface" on its own style, and touch the pollen grains produced by the flowers to complete self-pollination, which is not serious.
3. The fruit of Compositae is a dry fruit without cracking, with a dense peel and only one seed, which is generally considered as achene. However, it originated from carpels and formed in the lower position of ovary, which is different from the upper achenes of ovary formed by carpels. Strictly speaking, it should be called "Chrysanthemum Fruit" or "Cypsela".
Most of the inflorescences of Compositae plants are large and bright, suitable for insect pollination, but some genera and species have dull flowers, such as Artemisia, Xanthium and Ambrosia, and their inflorescences are small, yellow-green, and very bright. These plants are specialized types from insect vectors to wind vectors. Xanthium plants are monoecious, with different flowers and small male inflorescences. They still have flat flower heads, and the flowering period is very short. After the flowers wither, they fall off, which is often overlooked. The inflorescence axis (receptacle) of female inflorescence (so-called "Cangzi") is lignified, and there are many barbs outside, including two female flowers, each of which has only one ovary and two styles, and the whole inflorescence falls off when it matures.
Sunflowers are widely planted in all parts of China, with easy materials, large inflorescences and flowers, and easy observation. Here is a brief description of its various organs for teaching reference.
Sunflower is a large annual herbaceous oil crop originating in North America, and its seed oil content is 43.9 ~ 52%. 2 ~ 4 meters high, big heart-shaped leaves, alternate. The head is solitary at the top of the stem, generally 30 cm in diameter and up to 60 cm in size. The axis (receptacle) of the head is flat and filled with white spongy fillers (parenchyma cells). Inflorescence is surrounded by 3 ~ 4 layers of green involucre. The outermost flower is a bright yellow "tongue-shaped flower" (edge flower), and the center is a yellow-brown tubular flower (disc flower). Tongue-shaped flowers (see Figure C) are sterile and asexual flowers, whose function is to attract insects to visit and help pollinate. The base of the petals is connected into a short tube, and the upper part of the petals is flat and stretched, consisting of three petals, and the other two petals are degraded, so some people call it a "false tongue-shaped flower". Ovary triangular, ovule-free, style and stamens degenerate and no longer exist. Sepals degenerate into membranous "crown hairs", usually three, attached to the top of the three corners of the ovary. There are no obvious bracts at the base of ovary. Five petals of a tubular flower (disc flower) (see Figure B) are connected at the base to form a tubular shape with five teeth at the upper part, which are radially symmetrical. The lower part of the petal tube expands into a ball with cilia on it, which has two functions: 1. The enlarged cavity stores nectar for visiting insects. 2. The swollen parts are close to each other, filling the gap between corolla tubes to prevent rain, dust or long-nosed insects from damaging the ovary below. Sepals degenerated into membrane-like triangular sheets, attached to the two upper corners of the flat ovary, and had no obvious effect, and the fruit fell off when it matured. The anthers of stamens are dark brown, connected with the synthetic tube, and the connective is triangular and yellowish brown. The pistil ovary is inferior, white when immature, thin and soft, and the pericarp becomes hard and black when mature. Each ovary has a membranous bract at the base, which is white and has three teeth at the top. When the fruit ripens and falls off, this bract remains on the flat inflorescence axis.
Compositae plants are divided into two subfamilies, 12, according to the morphology of flowers in flower heads and the presence or absence of milk. The division criteria are:
Compositae plants do not contain milk, and the flower heads are all tubular flowers or at least the disk flowers in the inflorescence are tubular flowers. Including 1 1 family, most compositae plants belong to this subfamily. It should be noted that the daily cultivated chrysanthemum (Dendranthema morifolium) is the result of long-term artificial selection, although the disc flower in the middle of the inflorescence is like a tongue without milk, which belongs to this subfamily. Artemisia argyi, sunflower, etc. Also belong to this subfamily.
Chicory plants contain milk, and all flower heads are tongue-shaped. Contains only one series. Dandelion, lettuce and chicory all belong to this subfamily.
Compositae plants are closely related to human life. Among them, there are many famous ornamental flowers such as chrysanthemum, dahlia, marigold, marigold, chrysanthemum, wax chrysanthemum, cosmos (autumn English), chrysanthemum and daisy. Vegetables for daily consumption include lettuce, chrysanthemum (called Artemisia stem in Beijing), Jerusalem artichoke (ginger is not spicy), lettuce and so on. There are many kinds of medicinal materials, such as pyrethrum, safflower, burdock, Artemisia capillaris (the effective component of expelling ascaris in inflorescence-Shandaonian), Atractylodes lancea, Eupatorium adenophorum, Cirsium japonicum and so on. The plant that can extract aromatic oil is blumea balsamifera, the volatile substance extracted after distillation is borneol, and the whole Artemisia annua can extract aromatic oil. Dandelion is a kind of rubber resource plant in the cold region of northern China, which was cultivated in large quantities in the Soviet Union. Plants harmful to human life, such as some kinds of Artemisia, only grow in farmland and are the enemy of crops. The pollen of some ragweed plants is prone to allergic reactions to some people.