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Succulents - from the Latin succulentus - juicy. This is a group of drought-resistant plants capable of accumulating moisture in their organs (stems, roots, or leaves) and storing it for a long time, thus safely surviving the dry season. All succulents are xerophytes.
Xerophytes are plants in dry habitats that can withstand prolonged drought. All of them have their own adaptations to adapt to extreme conditions (prolonged heat and drought).
But not all xerophytes are succulents, for example, wormwood is a xerophyte, but not a succulent. Its method of adaptation is leaves and stems covered with small, dense hairs, which protect the leaves from excessive evaporation of water. Or camel thorn - an inhabitant of the deserts, it is not a succulent, but a xerophyte, its way of adapting to drought is a powerful root system, lying at a depth of several meters, to groundwater, and hard leathery integumentary tissues that reduce the evaporation of moisture.
In succulents, the root system, in contrast to sclerophytes (camel thorn), is relatively small and is located in the upper layers of the soil. Moreover, it does not depend on the size of the plant, for example, when transplanting a large specimen of the tree-like jellyfish, you can make sure that its roots are surprisingly small, thin, and fragile.
Classification of succulents
Leaf succulents leaf succulents are plants with succulent fleshy leaves (zamioculcas, aloe, haworthia, peperomia, bastard).
Stem succulents Stem succulents are practically all cacti, and euphorbia, in most of them the leaves are reduced to spines or completely absent.
Caudiciform caudiciforms are succulents with a thickened stem and hypothetical, in these plants the aerial part (stems and leaves) is thin, and the roots are thickened, usually located underground or partially above the ground (nolina, jatropha, morning glory, dioscorea, cacti are also found, for example, pterocactus tuberosus Pterocactus tuberosus). In these plants, the thickened part, as a rule, is all lignified, can be in the form of a ball or turnip.
Pachycal pachicauls are succulents with thickened hypocotyl and epicotyl, they have partially thickened roots, and the trunk is thickened only in the lower part, these are the so-called bottle trees (bursera, adenium, pachypodiums), they usually have a smooth transition of the trunk from the thin part to expanded, and lignification is observed only in the root zone.
The hypocotyl is the section of the seedling stem below the cotyledon node. The hypotic goes down into the root and often has an anatomical structure with features of both the stem and the root.
An epicotyl is a section of the stem of a seedling (or embryonic bud) of a plant between the cotyledon node and the node of the first true leaf, i.e. first internode.
Caudiciform and pachycal plants are usually considered in the same collection group because visually, the difference is difficult to detect at first glance.
As you can see, succulents do not include bulbous (for example, amaryllids), as well as plants with root tubers (for example, tuberous begonias). The fact is that the presence of any water-storing organ in a plant is not the only necessary criterion for classifying it as succulents. And even the ability to survive a prolonged drought in a "dormant" state is also not the basis for classifying a plant as a succulent.
Succulents include plants with a special physiology, and above all, photosynthetic features, the so-called CAM-type of photosynthesis. The name is an abbreviation for Crassulacean Acid Metabolism - acid metabolism of fatty plants.
Without going deep into chemical processes: during CAM photosynthesis, the stomata of plants that absorb carbon dioxide during the day, when transpiration is maximum, are closed, but open towards the night when transpiration is minimal. We remember from a biology course at school that photosynthesis occurs in the light, the process is impossible without the participation of solar energy, but succulents have adapted to this: carbon dioxide obtained at night is stored in the vacuoles of cells, where CO2 is preliminarily included in the composition of other compounds. During the day, they are included in the process of photosynthesis. At the same time, in non-succulents, carbon dioxide is absorbed during the day, and is immediately included directly in the Calvin cycle (C3 type of metabolism).
This mechanism is key to differentiating succulents from other types of plants. Moreover, the ability of some plants to undergo the CAM-type of photosynthesis makes it possible to classify some plants as succulents, although they are not commonly considered as such in wide circles.
We are talking in particular about orchids. Indeed, scientists have proven that almost all orchids that are epiphytes have the CAM-type of photosynthesis. It is paradoxical at first glance, because they often grow in tropical forests, under the crown of trees, and not under the scorching sun of the desert. However, this is the case. High humidity in the tropics, during the rainy season, is replaced by periods when the amount of precipitation is minimal, and the air humidity is very low at high daytime temperatures, which with the usual type of photosynthesis (with the daytime absorption of carbon dioxide) would be detrimental to orchids. In addition, the leaves of most orchids are succulent and thickened, capable of storing water.
The CAM type of photosynthesis was found in the following plant families (the list is not complete):
- Pepper Piperaceae, genus Peperomia - in some species of peperomia (Peperomia camptotricha), young leaves have the CAM-type of photosynthesis, mature leaves have a transitional metabolism, assimilate carbon dioxide, both day and night. You can call them semi-succulent plants.
- Cactaceae Cactaceae are almost all genera, only a few genera have a C3 metabolism, and in addition, seedlings of many cactaceae also have a C3 metabolism. This explains why the conditions for growing seedlings are significantly different from the needs of adult plants.
- Crassulaceae Crassulaceae, Purslane Portulacaceae, Aizoon Aizoaceae - most genera have a CAM-type carbon assimilation mode.
- Euphorbiaceae - genus Euphorbia Euphorbia, some species.
- Asteraceae - genus Senecio, some species.
- Aroid Araceae is the only succulent species. Zamioculcas zamiifolia has a CAM-type metabolism.
- Bromeliad Bromeliaceae - genus Tilandsia Tillandsia, Hechtia Hechtia, Dyckia Dyckia, almost all from the subfamily Bromeliaceae Bromeliaceae.
- Xanthorrhoeaceae Xanthorrhoeaceae - genus Aloe Aloe, Gasteria Gasteria, Haworthia Haworthia.
- Asparagus (asparagus) Asparagaceae are the genus of the subfamily of nolin: Sansevieria Sansevieria and Dracaena Dracaena, as well as the genus of the subfamily agave: Agave Agave and Yucca Yucca.
Succulents in the collections of members of the forum
Reproduction of succulents