It is believed that plants are derived from some ancestral structures that were located in the banks of some lagoons. From there, they began to develop specialized structures that anchored them to the ground. A few simple underground extensions originated roots, allowing the absorption of water and nutrients dissolved in the ground. After this evolutionary achievement, plants acquired stems and leaves that enabled them to efficiently gather solar energy and carbon dioxide, necessary for photosynthesis. Later, a new component would appear on the stems of ancestral stems, known as lignin, which granted rigidity and possibilities for stem growth and bifurcation. This way, little by little, plants increased in size and the stems began to develop ramifications (branches), favoring the capture of light on the part of leaves. Another milestone was the irruption of conductive systems for water and solutes, called vascular systems.
The evolution of plants lasted for a period of over 600 million years. The first were unicellular algae that originated the first plants. The origin of the superior groups is not yet well defined, as few fossils have been found that can explain the evolutionary situation experienced by these organisms millions of years ago.
What there is certainty of is that the appearance and colonization of the Earth’s surface by plants directly influenced the reduction of carbon dioxide present in the atmosphere and consequently eased the drop of the Earth’s average temperature, also allowing the development of new living organisms.
Main groups
Three great groups are recognized in the Kingdom Plantae: non-vascular plants, non-seed bearing vascular plants and seed bearing vascular plants.
Non-vascular plants are also known as Bryophytes. This group is made up of mosses, hepatics and anthoceros. They are considered the closest record there is of the first plants that populated our planet to this day. Generally, they are perfectly adapted to survive in permanently or seasonally humid habitats, being able to absorb water through their entire body surface. Their size is rather limited, the conductive tissues are frequently totally absent or not well differentiated when they are; there are no roots, leaves or real stems.
Vascular plants are those that do count with a system for transporting substances. Two large groups can be distinguished, told apart by their method of reproduction: the ones that lack seeds and those that have seeds. The first ones originated during the Devonian (416 million years ago) and today, they are commonly represented by ferns. They are characterized for having rather simple tissue (compared to seed bearing plants) and green stems that have a large surface, granting it a great ability for performing photosynthesis.
Non-seed bearing vascular plants reproduce through spores. The latter are formed in special organs known as sporangia, which are found in modified leaves called sporophylls.
Seed bearing vascular plants comprise the most complex evolutionary group of their kingdom. Their form of reproduction is considered the most successful, because, by having a specialized and safe structure for perpetuating their species, the seed has more advantages compared to the other groups of the kingdom, being the dominant plants in most of our planet’s habitats. At the same time, within this group it is possible to identify two subgroups: gymnosperms and angiosperms or plants and flowers, both differentiated by the presence or absence of a protective coating for the seed.
Importance for life
In terms of conservation, for many the protection of animal species is more relevant than that of plants. However this is a very erroneous view, because plants constitute the base of life on our planet, and the survival of any organism, including ours, depends on their existence.
Plants not only intervene is some of the most important ecosystemic processes, like the transference of carbon, oxygen and nitrogen, but are also present at the front line of nutrition for living organisms.
All green plants perform an important process called photosynthesis, which consists on transforming solar energy into chemical energy. This process is performed within the vegetable cells inside the chloroplasts, and , in general terms, occurs in the following way: the leaves of the plants have pores called stomas, the atmospheric gasses penetrate through here. One of these gasses is carbon dioxide (CO), which combines with water (H2O) inside the plant cells, forming carbohydrates and releasing oxygen (O2), which all human beings need. A chain reaction that enables the existence of the great majority of the living beings on the planet.
Human beings also use plants in thousands of ways. They are an important source of food, because leaves, stems, fruits, seed-casings, roots and branches are a part of our diet. Estimates say that approximately 7 thousand species have been used by Man as a source of nutrition.
Another of their traditional uses is medicine. Nearly one fourth of drugs currently in production worldwide contain active ingredients that come from plants, and another tidy percentage has compounds that imitate some found naturally in other organisms. So far, important drugs for diseases like cancer or leukemia are derived from plants, and only nearly 15% of the known species has had research conducted upon them, which grants potential opportunities for current medicine.
Plants also constitute an important source of fiber and fuel. Paper, ropes and many of the fabrics we use everyday come from them, while as fuel, wood or timber coal represents an important material used in some countries.
