Succulents - from 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 of dry habitats that can tolerate prolonged drought. All of them have their own adaptations for adaptation in extreme conditions (prolonged heat and drought).
But not all xerophytes are succulents, for example, wormwood is xerophyte, but not succulent. Her method of adaptation is leaves and stems covered with small thick hairs, protecting against excessive evaporation of water by leaves. Or the camel thorn is a desert inhabitant, it is not a succulent, but xerophyte, its way of adapting to drought - a powerful root system, lying at a depth of several meters, to groundwater, and tough leathery cover fabrics that reduce moisture evaporation.
In succulents, the root system, unlike sclerophytes (camel spine), 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 a stout tree, you can make sure that its roots are surprisingly small, thin, and fragile.
Classification of succulents
Leaf succulents leaf succulents - plants with juicy fleshy leaves (zamioculcas, aloe, havortia, peperomia, stoats).
Stem succulents stem succulents are almost all cacti, and euphorbia, in most of them the leaves are reduced to spines or completely absent.
Caudiciforms caudiciforms are succulents with a thickened stem and hypothecus, in these plants the aerial part (stems and leaves) are thin, and the roots are thickened, usually located underground or partially above the ground (nolina, iatropha, hypomea, dioscorea, cacti are also found, for example, pterocactus tuberosus Pterocactus tuberosus). In these extensions, the thickened part, usually all lignified, can have the shape of a ball or turnip .
Pahicual pachicauls are succulents that have a 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 (burser, adenium, pachypodium), they, as a rule, have a smooth transition of the trunk from the thin part to the dilated one, and lignification is observed only in the root zone
For reference:
The hypocotyl is the section of the seedling stem of the seed plant below the cotyledonous node. The hypothetical goes down to the root and often has an anatomical structure with signs of both stem and root.
The epicotyle is the section of the stem of the seedling (or germinal kidney) of the plant between the cotyledonous node and the node of the first present leaf, i.e. the first internode.
Caudiciform and pahicual plants are usually considered in one assembly group, because visually, the difference is difficult to detect at first glance .
As you can see, succulents do not include bulbous (for example, amaryllis), 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 a succulent. And even the ability to survive a long drought in a "dormant" state is also not the basis for classifying a plant as a succulent .
Succulents include plants with special physiology, and above all, the features of photosynthesis, the so-called CAM type of photosynthesis. The name is an abbreviation for Crassulacean Acid Metabolism.
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, and open by night, when transpiration is minimal. We remember from the biology course at school that photosynthesis takes place 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 cell vacuoles, where CO2 is previously included in other compounds. During the day, they are involved 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 (S3 type of metabolism).
This mechanism is key in distinguishing succulents from other types of plants. Moreover, the ability of some plants to CAM-type photosynthesis allows us to classify some plants as succulents, although they are not considered to be such in wide circles.
We are talking in particular about orchids. Indeed, scientists have proven that almost all orchids, which are epiphytes, have CAM-type photosynthesis. Paradoxically, at first glance, they often grow in tropical forests, under the crown of trees, and not under the scorching sun of the desert. Still, it is. High humidity in the tropics, during the rainy season, is replaced by periods when rainfall is minimal, and air humidity is very low at high daytime temperatures, which with the usual type of photosynthesis (with daily absorption of carbon dioxide) would be fatal for orchids. In addition, the leaves of most orchids are juicy and thickened, capable of accumulating water.
CAM-type photosynthesis was found in the following plant families (list not complete):
- Pepper Piperaceae, peperomia genus - in some species of peperomia (Peperomia camptotricha) young leaves have CAM-type photosynthesis, mature leaves have transitional metabolism, absorb carbon dioxide, both day and night . They can be called semi-succulent plants.
- Cactus Cactaceae are almost all genera, only a few genera have S3 metabolism, and in addition, many cactus seedlings also have S3 metabolism. This explains why seedling growing conditions differ substantially from the needs of adult plants.
- Thick Crassulaceae, Portulacaceae , Aizoaceae - most genera have a CAM-type carbon assimilation regime.
- Euphorbiaceae is the Euphorbia genus of Euphorbia, some species.
- Asteraceae is a genus of Senecio the Godson, some species.
- Aroid Araceae is the only succulent species Zamioculcas zamielystic Zamioculcas zamiifolia, has CAM-type metabolism.
- Bromeliaceae - Tilandsia genus Tillandsia, Hechtia Hechtia, Dyckia Dyckia, almost all from Bromeliaceae subfamily.
- Xanthorrhoeaceae - genus Aloe Aloe, Gasteria Gasteria, Haworthia Haworthia.
- Asparagus asparagaceae is a genus of the nolin subfamily: Sansevieria Sansevieria and Dracena Dracaena, as well as the genus of the agave subfamily: Agave Agave and Yucca Yucca.