They are the ones that make our garden beautiful, that make it happy, especially in spring, with the bright colors and delicate scents; but in fact the flowers, what function do they play for the plants?
Almost all plants produce flowers, although angiosperms actually produce "real" flowers, while ferns and gymnosperms (conifers) produce other structures to perform the function of flowers.
The flowers are the reproductive organs of flowers, within which the female and male gametophytes meet, through a process called pollination, carried out by insects, animals or by the wind.
The inside of the flower is divided into several zones, almost concentric, each of which has different functions:
- The outer part is called Calice, and consists of the sepals;
- Inside the sepals is contained the corolla, often the most colorful part of the flower, consisting of the petals.
- Among the petals we find a swollen, drop-shaped structure called gynaeceum; it is the feminine part of the flower, where the eggs to be fertilized are produced and released. The lower and elongated part of the gynaeceum is called the ovary and the upper part, often in the form of a filament, is called stigma, the set of ovary and stigma is called pistil.
- inside the flower is also present the androcean, or the male part of the flower, which produces and frees the pollen to fertilize the eggs; it is often drawn with more filaments, called stamens; the part similar to a petiole is called filament, while the upper part, where the pollen is contained, is called anther.
Obviously these parts so divided and clear can easily be seen only in some flowers, since each individual plant species has evolved differently, and therefore can present a corolla with petals joined to form a long tube, colored or shaped sepals of scales, a very enlarged or very small ovary, a single stamen or many. In addition, many plants produce inflorescences instead of flowers, or groups of flowers, such as the calla lilies or daisies, which bring together hundreds of flowers, the ones on a long stem, the others in a flattened disk.
Often the shape of the flower, its color, its perfume, is due to the way in which the plant is fertilized:
- Plants that transfer pollen through bees and hornets, or small birds, often have fairly simple, colorful and fragrant flowers.
- Plants that transfer pollen through other insects, such as flies, have flowers with bizarre shapes and a bad smell.
- Plants that transfer pollen by wind or rain tend to have unobtrusive and interesting looking flowers.
Moreover only the perfect flowers contain all the parts we have mentioned, in fact the plants can be divided into two groups, the monoecious plants, which have flowers consisting of attached androcean and gynaeceum, or even flowers with gynaeceum and flowers with only androcea on the same plant; and dioecious plants, which present flowers with the sole gynaeceum and flowers with the sole androceo; a typical example we all know is the actinidia, or kiwi, which has male flowers on some specimens and female flowers on other specimens: obviously these flowers differ greatly in shape.
Flowers and taxonomy
Botanists have been observing plants for centuries, using flowers and leaves as dichotomous keys to attribute a plant to a taxonomic genus; nowadays genetics is used, which in fact often confirms the taxonomy attributed through the observation of floral forms. Most floral forms are common and particular to every single species; for example, all asteraceae (or compositae) produce flower heads, flattened inflorescences, consisting of dozens of small flowers; all the orchidaceae produce flowers with very particular corolla, often with the two lower petals joined together to form an enlarged and elongated petal, called labellum; all the araceae produce inflorescences constituted by a species of panicle of small flowers without petals, subtended by a large bract, such as the calla lilies or the anthurium; and so on.
These characteristics also allow a simple gardening enthusiast to recognize an unknown plant he sees in the nursery, and in this way to be able to treat it with the right precautions.
Each plant then develops a flower that is a sort of modification of the shape of the perfect flower, obviously every floral shape or an inflorescence has a specific name, to be able to indicate them without misunderstanding; in addition to this it is possible to indicate a flower by writing the floral formula, or a simple symbolic phrase that brings together the characteristics of a flower. Generally it is a typical flower of a certain family, rather than a single flower, in the sense that it generally indicates the floral formula of the Liliaceae, not the floral formula of the tulip.
The floral formulas indicate how many petals and sepals form corolla and calyx, how many stamens and pistils contains the flower, the shape, etc., simply through a short string of text like this: Ca5Co5A10 - G1
indicates a flower with 5 sepals, 5 petals, 10 stamens and 1 pistil.
The various names that are attributed to floral forms usually depend on the shape attributable to the chalice or corolla, and they are many, given that there are so many forms of flowers existing in nature; in the same way there are many names that indicate the various existing inflorescences, even if we tend to generalize, and to combine the various inflorescences in a few indicative groups, such as panicle, umbrella, or the like.
So there are adjectives that indicate the shapes of the floral goblets: gamosepalo is the glass in which the sepals are all united until the apex, while the tubular is a chalice with the sepals united to form a thin tube; vesicular is the calyx with an enlarged shape that narrows at the apex, diasepalo is the calyx with the sepals very distant from each other.
Other adjectives indicate the flower in its entirety: apetalo is the flower without petals, which presents only the sepals of the calyx, while asepalus is the flower without sepals, without calyx; omomero is the flower that has an equal number of sepals and petals, on the contrary the flower which has a different number of petals and sepals is heteromeric; epigino is the flower that presents the ovary placed below with respect to the chalice and corolla, while the hypogeum is the flower with an ovary placed higher up than petals and sepals.
The names of the types of corolla often follow the names of the flower families with these forms, this indicates to us how much the shape of the flower is indicative and characteristic of every single family taxonomically indicated; therefore there are papaveraceae corollas, cariofillacee (of the carnation), papilionacee (of the legumes).
This happens because it is difficult to indicate with a single adjective a corolla of very particular shape; to indicate the less complex corollas there are proper adjectives, such as campanulata, or the typical bell-shaped, crown (narcissus), gamopetala when the petals are almost welded together or dialipetala when the petals are very distant.
In addition to this, the floral shapes also indicate how many are the petals that make up the corolla, adjectives that we are used to using, as a simple flower, double or stradoppio.
The Flower: The inflorescences
The inflorescences are groups of several flowers, gathered more or less close to each other; typical inflorescence is the ear, with a thin stem that supports numerous flowers, enlarged at the base; the raceme, or bunch, has flowers with a petiole that fits onto a stem; the umbrella instead has flowers with petiole inserted in the same point, to form a hemispherical inflorescence, when the petioles are of different length they give origin to a corimbo, that constitutes a sort of straight roof. The flower head is the typical inflorescence of the asteraceae, like the daisy, with a flat disk of small flowers, often with the outer crown of flowers having a single petal; the spadix is instead the inflorescence of the aracee, with a fleshy stem that supports dozens of small flowers without petals.
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