Ajuntament de Barcelona

The succulent plants

Mossèn Costa i Llobera Garden

    Agave Salmiana

    Succulent plants are able to accumulate water in the tissues, usually the stems and the leaves, giving them a swollen or fleshy appearance. They are also known for changing their leaves into prickles or by being covered by waxes or hairs, obtaining this way reduce the water waste because of the transpiration. Another strategy to survive in very dry environments is having a very extensive root system that allows them to explore and absorb easily the water in the ground, when available.

    Their water storage capacity makes them able to adapt to arid climate conditions or soils and to survive in terrains that are too dry for most of the plants, such as desert and semi desert climates.

    It is estimated that there are more than 60 families and 300 genuses of plants that have developed some type of resort to save water and to adapt to arid environments. You can find succulent plants in 30 botanical families, outstanding the Agavaceae, the Bromeliaceae, the Crassulaceae, the Euphorbiaceae and the most typical and one of the most numerous, the Cactaceae. The Cactaceae stand out because of the variety of shapes of their fleshy stems (rounded, columnar, arborescent...), where the prickles are placed into groups over a “cushion”, and because of very bright and colourful flowers.

    At Mossèn Costa i Llobera Garden you can see more than 150 species of cactuses, coming from America plants, and more than 200 other succulent plants, mainly from South Africa, as well as 12 species of palms. This one is the most relevant collection of cactuses and succulent plants in Catalonia and probably one of the world’s most important.

    Characteristics: 

    The plants adapted to live in drought conditions are called xerophytes and, along the evolution, they have developed strategies in order to survive in arid environments. There are basically two types of strategies: to collect the water from a wide area by a very extensive root system and to avoid wasting it. To achieve this, a series of morphological and physiological changes take place, depending on the type of adaptation to more or less extreme drought conditions. The main changes are having small, leathery and protected leaves with waxes or hairs and depressed and closed stomas, losing the leaves and, finally, the succulence, which is the most specialised and extreme adaptation (besides avoiding the water waste,  the plants store the water).

    Some plants have succulent leaves, made almost completely by water storage cellules that are covered by a thin tissue layer to do the photosynthesis (as the plants from the genuses Aloe, Haworthia, Lithops and Sempervivum).

    In other plants, the succulence affects the stems and the leaves have completely or almost disappeared in order to reduce the water evaporation surface (this is the case of most of the cactuses or of the Euphorbia obesa). In the most specialised cases, the stems are spherical: that reduces the relation between surface and volume and, in consequence, the evaporation surface. They also have folds, called ribs, that go longitudinally across the plant’s body and that allow some expansion and contraction, like an accordion, depending on the water that is stored in the body.

    Other plants have succulent roots: the fleshy and swollen roots store the water underground, far from the heat and the animals, whereas the leaves and the stems can fall during the dry seasons (Calibanus hookeri, Fockea edulis, Pterocactus kunzei, Peniocereus striatus).

    In many cases, the succulence occurs on several parts of the plant, for example on the roots and the stem (Ceraria pygmaea, Tylecodon paniculata, Namibian grape).

    From a physiological point of view, the succulent plants make a special photosynthesis named CAM (crassulacean acid metabolism). Unlike the rest of plants, in drought and high temperatures conditions, they open the stomas during the night and collect the CO2, storing it as an organic acid that is released during the day to be used in the photosynthetic process and to synthesise the food. By having closed the stomas in the maximal evaporation moments, they avoid the water waste to the fullest extent.

    These adaptations to drought, especially in the case of the succulence, make a slow growth.

    History and curiosities: 

    The popularity of the succulent plants as gardening elements has grown up by a bigger conscience of the water as a limited resource. In order to have an optimal growth and a maximal flowering, they have to be cultivated in full sunshine. Although they can resist more or less extended periods in drought conditions, if they have water available, their growth is much faster.

    Almost all the succulent plants reproduce easily in a vegetative way. From a leaf or a fragment of stem, you will have, in more or less time, a new plant that will be identical to the mother plant. Many of them can also reproduce easily via seed. To reproduce them, they have to be put in light and sandy substrate that have to be maintained wet, avoiding pools, because they will favour developing illnesses by funguses. 

    For further information: 
    Allaudia ascendens
    Cereus forbesii
    Silver torch
    Silver torch
    Golden torch
    Indian fig
    Trichocereus candidans
    Allaudia ascendens Cereus forbesii Silver torch Silver torch Golden torch Indian fig Trichocereus candidans