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Flowering plants (Angiospermae) represent one of the largest groups of primary producers. Their contribution to the production of oxygen as well as that to the nutriment of animals and man is consequently very large. All features reviewed in this chapter refer to seed-producing plants, also called spermatophytes.
Typically, flowering plants are organized into an underground root and a shoot above ground that consists itself of a stem and leaves. The organs of a plant that serve sexual reproduction are the flowers. Part of the pollinated flower ripens and becomes the fruit.
In contrast to many other plant groups, flowering plants are striking, numerous and common. They are the most important group of the so-called primary producers that generate the prerequisite for life on earth: oxygen. Green plants have the ability to convert solar energy into chemical energy (photosynthesis) producing the oxygen necessary for all other organisms as a by-product. The useable plants among the flowering plants are - directly or indirectly - the basis of human existence; they are, too, an important economical factor. A basic knowledge of flowering plants should therefore be among everybody's general knowledge.
Much has been written about flowering plants and every reader of this chapter will miss something that he regards worth knowing, while he might find other information trivial. But everybody will understand that it is impossible to review in a few lines a theme about which an extensive, partly popular scientific literature exists. And although this term may sometimes be used in a disparaging way, most of the popular scientific literature is scientifically correct, lucid and, above all, very well illustrated.
To get an idea of the variety of existing plants and to get to know special species, it is necessary to identify them. Many books on classification with different approaches exist. In many popular books, color photos or drawings are used and often is the color of the flower a primary feature of recognition. Most of the so-called scientific books on classification work on dichotomic keys, i.e. the user is asked a lot of questions in succession and has at each one to decide between two answers. This procedure is continued until the plant has been identified. The "scientific nature" is mostly based on the completeness of the varieties present in a book, since almost all of the illustrated books contain only the most common or most striking plants.
Recently, electronic tools have been used to figure out identification keys for plants. An example is the
developed by Ray PHILLIPS, Director of Information Technology Services and Assistant Prof. of Biology, Colby College, Waterville, ME 04901.
The research into the flora of Central Europe has a tradition that goes back for centuries. It is mirrored in the nearly complete modern floras and books on classification. Incomplete, if existing at all, are books on the classification of less well discovered regions, like tropics, subtropics and many mountain areas.
The question of the origin of the wealth of forms (evolution) is discussed elsewhere where it is also shown that mountains with their rather small and isolated areas provide ideal conditions for the coming into being of new species. This is the reason, why even very experienced botanists equipped with renowned books on classification of the Central European flora will sometimes and in some places fail (Alps).
This chapter will deal with the characteristics of flowering plants that produce seed (phanerogames or spermatophytes) only. Many of the structures present in this plant group can be found with other non-flowering plants, too. But mosses, ferns and algae miss some features, like flowers or seeds while others, like roots or leaves exist in an incomplete way or are replaced by other organs.
The body of vegetation of many-celled algae (and mosses) is called thallus, that of flowering plants, ferns and fern-like plants (pteridophytes) is called cormus. The latter are therefore summed up as cormophytes. The special features of the different plant groups will be discussed later.
The body of vegetation of a "typical" flowering plant consists of an underground root and a shoot above ground. The shoot is organized into stem and leaves. Each of these basic organs can exist in many variations and these again can be combined in many different ways. The almost unlimited ability of combination is one of the main reasons of the existence of such a high number of species while at the same time, the identification of the relations of the species is aggravated.
If seemingly different organs with different functions can be traced back to the same basic organ, they are called homologous. It is also spoken of homology. Contrasting is analogy where organs with a similar look and function have descended from different organs.
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