Psilophytes are one of the first inhabitants of the land on the surface of the ancient Earth. Along with mosses and lichens, they were able to adapt to life outside the seas and ponds. From them began the evolutionary development of all other "land" plants. Due to the fact that rhinophyte petrification occurred under favorable conditions, scientists have the opportunity for a detailed study of the flora of our planet, which existed more than 400 million years ago.
The first plants are psilophytes
Psilophytes are an outdated name for riniophytes, the most ancient and most primitive department of higher plants. The name of this group of representatives of the plant world comes from the Greek word psilos, which means “naked” or “bald”. Their appearance refers to the Devonian period in the geological history of the Earth (419-358 million years ago). Around the same time, mosses and mushrooms arose.
The similarity of psilophytes with algae indicates their evolutionary kinship. Disappearing sections of the seas and other bodies of water forced aquatic plants to adapt to life on land. When drought occurred or water left, those algae whose roots were better developed survived.
Rhinophytes inhabited all continents, but environmental conditions that changed at the end of the Devonian became unfavorable. As a result, these representatives of the ancient flora are completely extinct. From psilophytes, modern plants of the department of the plow-like, horsetail, fern and gymnosperms originated.
Features
Psilophytes are primitive vascular plants. Their feature is that the conducting system consisted of a haplostela, the simplest complex of tissues located inside the cortex. The height of rhinophytes was 40-70 cm (sometimes up to 3 m), and outwardly they looked like algae. Their structure has not yet been divided into organs. The stalk of rhinophytes was uniformly branched. Outgrowths of the epidermis were found in some psilophytic plants, from which leaves later developed during evolution. The process of photosynthesis was carried out in the stems.
The organs producing spores (sporangia) were located on the tops of the plant (less often distributed along the stem). They had a spherical or cylindrical shape, and in size amounted to 1-12 mm. In them, spores matured, which dispersed in the environment. The nature of the propagation of the first psilophyte plants is not reliably known. There is an opinion that sporangia grew on separate diploid shoots that had 2 complete sets of chromosomes, and the rest of the plant body was haploid.
Psilophytes are inhabitants of humid and swampy places, but among them there were completely “land” ancestors of higher plants. Since it was necessary to protect the surface mass of the plant from drying out, gradually the epidermis appeared with stomata that regulate the evaporation of moisture. In the lower part of the rhinophytes there were filiform formations (“rudiments” of roots, rhizoids) from one or several single-row cells. With their help, there was a process of absorption of water and nutrients.
Discovery story
The first discovery of fossil psilophytes was made in 1859 by the geologist D. Dawson on the Gaspe Peninsula in Canada. The scientist gave the plant the name Psilophyton princeps, which is translated into Russian as "primary holos." At that time, this find was not given much importance. Perhaps the main reason was that psilophyte was very different from modern plants and did not fit into the existing botanical classification.
In 1912, W. Mackey discovered strata of siliceous rock near the village of Rainey (Scotland). The soil contained well-preserved plant debris. He transferred these samples to the paleobotanist R. Kidston, whose studies laid the foundation for a systematic study of the oldest representatives of the flora. R. Kidston and W. Lang have established that psilophytes are similar to the genera of rhinium and chorneophyte.
In 1937, Lang found a new genus of plants in the older sandstones of Scotland, which was called kuksonia. In modern paleobotany there is no unequivocal opinion about the belonging of kuxonia to the rhinophyte department, at present it occupies an uncertain position.
Rinium class
In the rinium class, several families are distinguished (Rhyniaceae, Horneophytaceae and others). The most studied psilophytes are rhinium and chorneophyte. The largest was rhinium large, which reached a height of 50 cm. A unique feature of fossil plants is that they are very well preserved, down to the smallest details of the anatomical structure. This happened as a result of favorable factors during their petrification and saturation of tissues with silicon.
Under the epidermis with stomata, rhinia and chorneophyte bark was located, the cells of which carried out the functions of photosynthesis. Root rhizomes consisting of tuberous segments were found in the chorneophyte. With the help of rhizoids, these plants could reproduce vegetatively. Chorneophyte sporangia resemble similar organs in modern sphagnum moss.
Other studied representatives of this class are Yraviya, Hedeya and shadowirada.
Zosterofill class
In primitive plants of the class zosterophyll leaves are also absent. Presumably, they laid the foundation for the development of the department of the plaids. The most prominent representatives are the zosterofillum and glossling, an interesting feature of which is the spiral twist of the upper part of young shoots.
In zosterofillum, sporangia are collected in spike-like formations. The plant was adapted to survive in saline places, as evidenced by the presence of a thick wax-like skin on the stems.