Origin of ferns
Most scholars believe that ferns originated from naked ferns in the Silurian and Lower Devonian periods 400 million years ago, while naked ferns are believed to have originated from algae plants, especially green algae, for specific reasons, which are specifically introduced in the microheadlines of my algae. Some scholars also believe that ferns originated from mosses, the specific reason is that the sporophyte shape of naked ferns is similar to that of hornwort, but in this generational process, the advantages and disadvantages of sporangia and gametophytes of ferns and bryophytes are so different, or even completely opposite, which cannot be explained. Some scholars believe that both ferns and mosses originated from algae and evolved in parallel.
You may be wondering, how did the early terrestrial plants on Earth adapt to life on land? After all, compared to algae and mosses, ferns have a clear ability to adapt to terrestrial life, and are the first two more advanced species types in the evolution of gymnosperms and angiosperms to terrestrial higher organisms.
At the end of the Silurian period 400 million years ago, the living environment of aquatic floating plants and aquatic plants has undergone great changes, mainly land uplift and water level decline, so that a large number of plants are exposed and directly exposed to the air, because these duckweed-like aquatic plants originally mainly rely on water buoyancy to maintain their body shape, and now they can only be squeezed and overlapped, but part of these plants are upturned upwards, contact with more light and sufficient gas exchange, and the result is vigorous growth, But these parts also need water supply, otherwise it is easy to drought, and without water, it is more difficult to obtain nutrients, so how do these plants with upturned parts solve these difficulties?
Take the naked fern as an example to introduce this process, the lenny fern in the naked fern existed in the early Devonian, is the earliest terrestrial plants, they are only 18-50cm tall and simple structure, there is no differentiation of rhizomes and leaves, but there is already a flat rhizome and aerial stem differentiation, the rhizome has a single-celled pseudoroot, the aerial stem is somewhat bifurcated, and there are stratum corneum and stomata to regulate the transpiration of plants, there is a middle column in the stem, this middle column is composed of wood and mechanical tissue, It not only helps ferns transport water and nutrients, but also increases the fern's support capacity, while pseudoroots absorb water and inorganic matter, and aerial stems help exchange gas, which is the adaptation of primitive ferns to land uplift and water surface decline, and the result of natural selection also makes plants take an important step towards landing.
The sporangia of the leni fern are at the top of the branches, raised high in the air, the sporangia are composed of multiple layers of cells, which has a great effect on the poor water absorption ability of early plants and the protection of excessive evaporation of water, and the sporangia can not spread spores, the outer layer of spores is tough, and plays a protective role in a dry air environment, which shows the evolution of aquatic plants to land-based plants, and the ancestor of ferns, naked ferns, has made great contributions.
Plants can evolve from aquatic to terrestrial, supporting plants, here taking the leni fern as an example, it is very important to support the middle column of the lenny fern standing upright on land, so what is the structure of the central column?
The central column of the lenny fern is a single central column, but the middle column of ferns like pine leaf fern is formed by spinous processes formed by the expansion of the xylem to the periphery, which is the star-shaped middle column; Similar to Stone Pine, because the phloem invades the xylem, causing the xylem to be interrupted continuously, forming a woven central column; These three types of middle columns do not have a pith, so they are called primitive middle columns.
More primitive ferns continued to evolve, evolving more complex vascular tissues, and pulp appeared in plant bodies, such as cypress, and most ferns, such as ferns, appeared reticulated mid-column. The most advanced middle column is divided into two types, the first is the middle column of angiosperms and gymnosperms, which are xylem and phloem parts arranged in two bundles, called true middle columns; The other is the middle column of monocots, which is the scattered middle column formed by the vascular tissue scattered in the cortex.
Naked ferns are divided into three phyla, namely Lenny fern, Gongfern, and Three-branched fern.
At the end of the Devonian, violent crustal movements made the climate more arid, and gymnoferns could not adapt to this arid environment and went extinct; However, plants that evolved on naked ferns with complete vascular systems began to be called land plants dominant.
These ferns that dominate the land, in order to further adapt to land life, organs are constantly evolving, there are many specific evolutionary theories, but the discovery of naked fern fossils provides evidence for the branch top theory.
The branch apex theory believes that the leaves evolved from the apical branches of the primitive vascular bundle ferns, large leaves are flattened by a large number of apical branches, and small leaves are flattened from a single apical branch. The spore leaves evolved from the side of the fertile apical branch, which caused the original top-growing sporangia to grow to the edge of the spore leaves. Among them, the spore leaves and sporangia of the subphylum Pinus lithophylum evolved from the same apical branch; The shield-shaped sporangia of the cuneiphylum evolved from the bending and merging of the apical bundles of the sporangia.
By the time of the Devonian and Carboniferous periods, these ancient ferns flourished, called the large area of forest that covered the earth, which was also the main raw material for the formation of fossil fuels that are now widely used.
#Naked fern##Lenny fern##Lenny fern##Worker fern##Three-branched fern##True middle column##Scattered central column##Devonian##Did the Carboniferous period really have a global rainforest##石炭纪也叫巨虫纪, why is it called Carboniferous?##Aerial roots##Aerial branches##False roots##孢子囊 #
