Pteridophytes are widely distributed in plains, forests, grasslands, crevices, gullies, swamps, mountains and water, especially in tropical and subtropical regions.
There are about 12000 species of ferns growing on the earth, most of which are herbs. There are more than 2,600 species in China, most of which are distributed in the southwest, the provinces south of the Yangtze River basin and Taiwan Province Province. There are more than 1000 species in Yunnan province alone, which is a veritable "fern kingdom".
Pteridophytes are mostly primary, lithophytic or epiphytic plants, and a few are aquatic or underwater plants, which generally show the characteristics of liking humidity and temperature.
The morphological structure of ferns is more complicated than that of bryophytes. Most sporophytes are perennial herbs, and only a few are annual. Except for a few primitive species with only false roots, they all have adventitious roots with good absorption ability. Stems are usually rhizomes, and a few are upright trunk-like or other forms of aboveground stems. A few primitive species have both aboveground stems and rhizomes, and the vascular system in the stems forms steles. The types of steles in ferns are extremely complex, mainly including primary steles, tubular steles, reticulate steles and multi-ring steles. These different types of steles are related to evolution, which is the trend from solid primary steles to scattered steles.
Vascular system consists of xylem and phloem, which are used to transport water, inorganic nutrients and organic substances respectively. Xylem is mainly composed of tracheids, and the wall thickens in a ring, line, ladder or other shape. Some ferns also have vessels, such as Lycopodium and bracken. However, there is no significant difference in the size of vessels and tracheids in ferns. In addition to tracheids and ducts, xylem also has parenchyma. The main components of phloem are sieve cells, sieve tubes and phloem parenchyma. In modern ferns, except for a few species such as Isoetes and Hedyotis diffusa, there is generally no cambium structure.
There are two kinds of leaves of ferns: lobules, such as Pteris, Lycopodium and so on. The petiole has only one unbranched vein. The source of small leaves comes from the epidermis of stems, which is the primitive type. The big leaves have petioles, the vascular bundles have or have no leaf gaps, and the veins are multi-branched. Its origin is formed by flattening most of the top branches. The leaves of Spodoptera exigua are all big leaves, which are progressive. Among the leaves of ferns, there are leaves that only carry out photosynthesis, which are called vegetative leaves or sterile leaves, and leaves whose main function is to produce sporangia and spores, which are called spore leaves or fertile leaves. The vegetative leaves and spore leaves of some ferns are indistinguishable and have the same shape, which is called isomorphic leaves. There are spore leaves and vegetative leaves with completely different shapes, which are called heteromorphic leaves. In the process of systematic evolution, isomorphic leaves develop towards heteromorphic leaves.
The sporangium of ferns, in pteridophytes, is solitary in the axils or basal parts of paraxial leaves, and leaves usually gather at the top of branches to form a ball or spike, which is called spore spike or spore bulb. In more evolved true ferns, sporangia are usually born on the back, edge or a specialized spore leaf, and are often formed by many sporangia, which are called sporangia groups or sporangia piles. The sporangia of aquatic ferns live in specialized sporangia or pods.
Most ferns produce spores with the same size, which is called spore isomorphism, while Selaginella and a few aquatic ferns produce spores with different sizes, which is called spore allotype. Isospore and heterospore can be divided into two types in morphology. One is a kidney-shaped, single-slit, bilaterally symmetrical dichospore; The other is round or obtuse triangle, three slits, tetragonal spores with radiation symmetry. The outer wall of spores usually has different protrusions and ornamentation. Spores undergo meiosis when they form, so the chromosomes of spores are haploid.
Spores germinate and form gametophytes. Gametophyte, also known as prothallus, is small in size, simple in structure and short in life. The original gametophyte is a block or cylinder with radial symmetry, which is buried in the soil or partially buried in the soil, and obtains nutrition through mycorrhiza, such as psilotum nud nm(l .))Grised. A few kinds of gametophytes are filamentous, such as Schizaea. The gametophytes of most ferns are green leaflike bodies, which have ventral differentiation and can live independently. The ventral surface produces archegonia and spermatogonia, which are similar to bryophytes, but the sperm has flagella. The gametophytes of heterospore species, such as Selaginella and aquatic ferns, develop within spores and tend to lose their independence. Sperm and eggs produced by gametophyte cannot be fertilized without water. The fertilized egg develops into an embryo, and the young embryo is temporarily parasitic on the gametophyte. After growing up, the gametophyte dies and the sporophyte lives independently.
In the life history of ferns, there are two independent plants, namely sporophyte and gametophyte. From the germination of fertilized eggs to the meiosis of spore mother cells, this process is called sporophyte generation, or asexual generation, and its cell chromosomes are doubled (2n). The stage from spore germination to sperm-egg combination is called gametophyte generation, or sexual generation, and its cell chromosome number is haploid (n). In its life, generations alternate obviously, and sporophyte generations occupy a great advantage.
In ferns, there is a phenomenon that sporophytes produce gametophytes without spores, which is called apospory. At the same time, gametophyte can also produce sporophyte directly without gamete combination, which is called apomixis. Agamemt reproduction is quite common in ferns, and sometimes in a plant, both Agamemt reproduction and apospory phenomenon can occur at the same time. Many gametophytes produced in apospory can normally produce sperm cells and archegonia, and the number of chromosomes of this gametophyte is 2n. The gametes produced from it cooperate to form a 4n sporophyte. This tetraploid sporophyte can also be induced to form tetraploid gametophyte of apospory. The diploid gametophyte induced by apospory, a true fern, can also mate with the gametophyte of haploid chromosome, thus producing triploid sporophyte.
In apogamy, sporophyte can be produced by a single vegetative cell of gametophyte, or by cells near or inside the archegonium, or an egg can directly form sporophyte without gamete combination, which is called parthenogenesis.
Botanists have great differences on the classification system of pteridophytes. In the past, pteridophytes were usually regarded as a natural group and classified into pteridophyta, and pteridophyta was divided into pteridosubfamily, lycopodinae, eguisetinas and pteridophyta. Someone added equipotential to these four categories and changed them into five categories. There are still four classes upgraded to four or five. 1978 "Pteridophytes of China" divides pteridophytes into five subfamilies, namely Lycopodium, Isoptera, Pteridoptera, Pteridoptera and Pteridoptera. This book adopts a new system and is divided into five sub-doors.