Plants: 350 thousand different species
The most widespread plants are part of the Angiosperms, which include about 250 thousand species. The study of species is entrusted to the branch of biology called botany. From a biological point of view, plants are defined as all the species that have certain characteristics. In particular, these are autotrophic organisms (that is to say, they are able to obtain their nourishment from inert substances such as soil, water and air) consisting of eukaryotic cells (that is to say advanced cells constituted by a true nucleus and own) whose walls are characterized by a high quantity of starch and cellulose. In order to survive, they carry out photosynthesis, that is biochemical reactions in sequence that allow to transform the captured solar energy, and in particular to convert carbon dioxide into sugars. The most important source of phytomass (organic matter) and energy for algae and plants of most ecosystems is represented by photosynthesis. The plant species, moreover, in the terrestrial ecosystems are the primary producers in virtue of the autotrophy, which makes them constitute the starting point of the food chain. Not only: they also play an important role in the context of numerous biogeochemical cycles, including the water cycle.
Coevolution with animals and symbiosis with fungi
The coevolution of plants has often been accompanied by a coevolution of numerous animals, thus giving a mutualistic association. The plant species, in essence, offer food to the animals, but also sites for reproduction and dens; animals, on the other hand, can favor the dispersion of seeds or pollination of flowers (in this case we speak of pollinators). To give an example, the evolution of myrmecophytes occurred at the same pace as that of ants, which contribute to defending such plants from plant species that are competitors or herbivores, and also fertilize them with their organic waste. Other types of symbiosis, however, can occur through the roots with some fungal species. In this case, an association called mycorrhiza is created, as a result of which the plant makes the carbohydrates derived from photosynthesis available to mushrooms, while in exchange it receives help in terms of absorption of nutrients and water present in the soil. It can also happen that some plants in their interior receive endophytic fungi, whose task is to protect their "home" from herbivores through the secretion of toxins. Suffice it to say that the orchid family, whose seeds do not have endosperm, can germinate only with the help of a specific fungus.
A particular species: carnivorous plants
A particular type of plant is represented by carnivorous species. These are herbaceous species which, as a result of the absence of nutrients within their habitat, have adapted by choosing to find the nutrients produced through the digestion of animal proteins. In practice, plants capture animals through traps, usually consisting of modified leaves: not just insects, but also other types of small animals or arthropods. Generally, these species live and grow in extreme environments: in acid soils, in peat bogs, in soils without calcium and in any case on substrates that have a very reduced concentration of potassium, phosphorus and nitrogen. Despite their rather impressive size, the roots are very small. The reason is quickly told: the search for nutrients does not take place through the root system in the soil, but through the leaves. For this reason, the plant uses its own resources to synthesize digestive enzymes, instead of trying to develop radical biomass. The leaves, in practice, need to absorb nutrients. The carnivores can be annual or perennial, and some are able to constitute colonies through the formation of stolons. Compared to other species, they prove to be rather weak competitors. In the event that their habitat undergoes drastic changes (for example, a sudden drying), they can be supplanted by non-carnivorous species, which are definitely more efficient in photosynthesis.
Instead, those that are grown at home are called ornamental plants. They, however, can be grown both in the ground and in pots. The general cultivation rules require that the soil be prepared in advance by means of digging, and then proceed with the insertion of the fertilizer. Afterwards it will be the time of weeding, with the removal of weeds, and more or less frequent irrigations depending on the species or the season. It is good to pay attention to plant diseases due to the presence of plant or animal parasites, which in some cases risk damaging the plant definitively. Finally, to favor its growth, it must be subjected to topping, thinning and regular pruning, which favor a better absorption of light, an optimized oxygenation and a more pleasing aesthetic appearance.