What are succulents or crass?
Evolutionary history, main families and habitats.
Q & A: Questions and answers about succulents and their origins
First things first: "succulent" plants are not a taxon! The term succulent is used to refer to a type of plant that has the ability to store and accumulate water in some of its organs that over time have specialized in it.
Cacti, for example, are succulents although not all succulents are cacti!
1. What does it mean for a plant to be succulent? What is succulence?
According to the Strasburger Treatise on Botany, succulence is when plants "store (water) in special aquifer tissues during short periods of rain and reserve it for times of shortage, often prolonged. Sometimes, it is the epidermis that which develops constituting an aquifer tissue of one or more cell strata [...]; sometimes subepidermal cells; at other times this aquifer tissue is located deeper (internal parenchymal aquifer tissue, for example, in the leaves of Aloes , Mesembryanthemum or Lithops.) When, in this case, it reaches a strong development, the respective organs acquire for this reason a fleshy consistency; such plants are called succulents.
In simple words, they are the plants that have developed the capacity to store and accumulate water, constituting an aquifer tissue inside to support the habitats and climates in which they live.
2. What is the origin of succulents?
Succulent plants grow almost everywhere on the planet! Their original habitats are Mexico, California, Africa (especially South Africa), mountain ranges in Central Europe, America, India and so on ... The important thing is to know that the vast majority of them come from very arid climates with a scarcity of rain. .
3. And then, if they come from different places, why are they so similar?
Suculence is developed by multiple plants of different families and genus, even of different geographical origin! This capacity works as a method of adaptation to very arid climates where rainfall is short-lived and rather scarce. And so how did they all arrive at this evolutionary solution without being related? This is one of the very curious examples of convergent evolution, where different plants that are not related to each other, have developed the same response to a certain condition or circumstance. In this case, it is the arid climate with short and rather scarce rainfall, with long periods of drought and a lot of solar radiation.
4. And if they are not related to each other, what families do they belong to?
The main families that contain succulents are the Aizoceae (Faucarias, Conophytums, Fenestrarias, Lithops), Asparagaceae (Ágaves, Yuccas), Apocynaceae (Adeniums, Ceropegias, Hoyas, Pachypodium, Orbea, etc.), Asphodelaceae (Haworthias, Aloes, Gasterias, Gasterias, etc), Asteraceae (Curios, Senecios, Crassothonas, Kleinias), Cactaceae (Echinopsis, Eulychnias, Mammilarias, Epyphyllum, etc.) Crassulaceae (Echeverias, Crassulas, Pachyphytums, Aeoniums, Sedums, etc), Euphorbiaceae (Euphorbias).
But beware: even if a family of plants contains succulents, it does not mean that all the plants that belong to that family are succulents. For example, the Asparagaceae family contains the genera Agave and Pasithea (to which our beloved Pasithea coerulea, native of Chile, better known as azulillo, belongs). Agaves are succulent plants, but Pasithea is not, as they both belong to the same family.
5. What is CAM metabolism? And why is it so special?
CAM metabolism or Crassulacean acid metabolism, so called because the first time it was discovered was in plants of this family (Crassulacea), is a mechanism through which the stomata that absorb CO2 from the atmosphere, do so at night when the temperatures are lower and not during the day, like the common of the plants that do it via C3 or C4. They reserve this CO2 in a cellular organelle called vacuole, in the form of malic acid and it is fixed during the day in photosynthesis (Calvin cycle). Why do they absorb CO2 at night? Because in this way they lose less water through perspiration, when opening the stomata. It is a tremendous adaptation to the environment where these plants live, where there are immense levels of solar radiation and very limited access to water. How smart, right?
Do you have any more questions? Check out the blog posts here!
Notes:
Here are some pages with more information in case you want to continue studying this wonderful world of plants!
SOURCES OF BOTANY and TAXONOMY
- https://chileanendemics.rbge.org.uk
BOTANICAL GARDENS:
- https://www.kew.org/science/collections-and-resources/data-and-digital