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Plants in nature tend to adapt to the most disparate conditions; to do this, many plants have taken on very particular forms, which we manage to bring back to the concept of plant. A typical example is represented by the succulents that we commonly call living stones; these plants belong to different genera, but they are all from the same family, the aizoaceae, and live in the arid areas of southern Africa.
The physical conformation of these plants makes them in fact suitable for life in desert or semi-desert areas, with scarce rainfall and a climate characterized by strong temperature changes during the day. All species have a similar conformation, ie each plant produces two broad leaves, generally supported by a short stem that generally develops underground, consisting of the fusion of the first part of the two leaves; during the development of the plant new leaves develop in the area of union between the two old leaves, which dry up while the new ones develop. Plants that grow in nature show only the upper surface of the two leaves in the open air, the underlying part only comes out of the ground in case of poor brightness; among the leaves also the large flowers bloom, often fertile, and often wider than the pair of leaves. From the seeds new plants will originate, therefore it is not uncommon to find real colonies of living stones.
The frithia and fenestraria species are exceptions to this general rule, as they do not produce coupled leaves, but numerous small cylindrical leaves close to each other.
The development of living stones
As we said above, the plants of lithops, pleiospilos, conophitum, develop only a pair of leaves at a time, therefore from the root rises a sort of short stem, on which develop two leaves, very appressate, shaped like an inverted truncated cone , with the base upwards, outwards and in the sun; over the years these plants can develop additional pairs of leaves, to form small colonies. If a plant receives the correct hours of sunshine every day, from the outside we only notice the surface of the two leaves, which come out of the ground for a few millimeters.
The leaves tend to develop in the fresh and humid months, and to enter in vegetative rest in the hottest and dry months; therefore in general the vegetative season of these plants occurs from the end of summer until late spring. During the summer the plants are in complete vegetative rest, when the temperatures are lowered and the climate becomes cool between the leaves the flowers begin to develop: they are large inflorescences similar to daisies, white, yellow or pink, often perfumed.
After flowering, the plant can begin to develop leaves near the pair already present; in winter the leaves produce a pair of new leaves starting from the line that divides them. These new leaves will grow at the expense of the old leaves, absorbing the water supply. Then the old leaves will dissect completely, to leave space for the new ones, which by the end of spring will have reached the size of the previous leaves.
Fenestraria, frithia and faucaria instead develop many neighboring leaves, in compact colonies, in the case of the faucaria they are also mated, but we can see more pairs of leaves that develop from the same short stem, while for the other two plants they are leaves single, which develop close to each other. These three species do not have a development similar to the others, so we will not see the succession of new and old leaves, the one at the expense of the others.
The behavior, the development, the appearance of these plants, clearly denounce the particular conditions of cultivation in which they grow in nature; the fleshy leaves collect large amounts of water, in order to withstand long periods of drought. Some of these plants live in areas of the planet where the rains are sporadic, so to survive they must be able to take advantage of every single drop of water they receive.
The underground development allows the plants to shelter from intense heat, avoiding evaporation from the surface of the stem; in addition to this the plants in this way avoid being eaten by wild animals, which otherwise would take advantage of these small reserves of water, succulent and crunchy.
The upper part of the lithops leaves, fenestraria and frithia, has a particular translucent aspect: these leaves on the upper pages are free of chlorophyll; this particular conformation is called window, as the transparent epidermis allows the sun rays to penetrate the plant, until it reaches the underground areas of the stem, where photosynthesis takes place.
Also the particularity of the new leaves that develop at the expense of the old ones is an expedient to limit the dispersion of water; the precious liquid contained in the dying leaves is in fact used by the new leaves, contrary to what happens in a deciduous tree, which leaves without problems that its leaves fall on the ground.
Living stones: how living stones are cultivated
These plants therefore come from areas of the planet characterized by high daytime temperatures, dry climate, low rainfall, and strong brightness.
To enable them to develop better we will have to try to imitate these conditions.
First of all we start from the soil, which must be very well drained; little universal soil is used, mixed with pumice stone, lapillus or pozzolana, in order to prepare an incoherent and stony substrate, where the water penetrates very quickly, without creating any kind of stagnation.
The plants will then be placed in a very bright place, in winter we can also place them in direct sunlight, while in the remaining months it is preferable to have a bright half-shade; ideal would be a greenhouse, with some glasses painted white, but also a window sill with a light curtain can be perfect.
The climate must be warm, because these plants do not like temperatures below 5-8 ° C, so they can be grown at home throughout the year, provided they are placed in a bright place.
The waterings will be sporadic throughout the year, decreasing them in summer, intensifying them in autumn, when the plants are about to bloom and are preparing for a period of vegetative growth; water the soil only when it is dry, and avoid wetting it in depth; rather one tries to wet only the few superficial centimeters of the substrate. Between one watering and another one always expects the substrate to dry completely; in indecision it is better to water once less rather than once too often.
Generally these plants, despite their bizarre shapes, are not of difficult cultivation, also because in the home they find a warm and dry climate, not completely dissimilar from that of places of natural origin; however, we pay great attention to never damage the leaves in any way, because usually even a small involuntary scratch leads to total and irreversible desiccation.