What are Succulents?

What Is a Succulent?

A succulent (from the Latin word 'succos', meaning juice) is a plant that has evolved various ways to survive its hostile environment.  These plants are able to store moisture in succulent tissue that either occurs in their leaves (Lithops, Haworthia), stems (Huernia, most cacti) or rootstock (Brachystelma, Ceropegia).  One of these features is prominent in all succulents.

Leaf Succulents

In species that are classified as leaf succulents, nearly the whole leaf is composed of water storage tissue.  Leaf succulents have extremely short stems which may appear to be non-existent.  The entire leaf is covered in a thin layer of assimilating tissue that absorbs water and carbon dioxide and converts them to food.  

Different species have evolved different methods to prevent water loss.  crassulas have a wax-like skin to prevent water loss, lithops and conophytum have a small evaporative areas while other species form rosettes (aloes, haworthias, etc) with compacted leaves which gives the plants protection from the sun, these rosettes also prevent moisture loss from the plant as well as the underlying soil.  In times of extreme drought leaf succulents will shed their leaves.

Examples of leaf succulents, Lithops dorothea and Haworthia retusa

Stem Succulents

Stem succulents are plants that have few or no leaves, the leaves that do appear tend to be short-lived before they shrivel up and fall off.  The absence of leaves aid in the prevention of loss of water through evaporation.  

The task of assimilation and transpiration becomes the responsibility of the fleshy green stems, shoots and temporary leaves (if they develop).  Many species have angled stems, wax-like skin or a fine coating of small hairs (Huernia pillansii) to prevent water loss.

Examples of stem succulents (Huernia pillansii, Euphorbia esculenta).

Root Succulents

Root succulents survive long periods of dry-conditions or drought by storing nutrients and water below the surface of the ground in tuberous or swollen roots.  The tubers being below the soil further decrease moisture loss.  There are additional benefits to having an underground water storage system; the tuberous or swollen roots are protected from damage by veldt fires and grazing animals.

Many of these succulents leaves and stems are deciduous, the leaves and stems are shed during the species dry season  (Brachystelma meyerianum, Ceropegia konrathii).  These leaves and stems in some species are thick and succulent which increases the plants water-storage capacity.

The task of assimilation and transpiration become the responsibility of the deciduous leaves and stems that appear during the growth season.

Ceropegia konrathii - Root Succulent

Caudiciform succulents or Cryptic succulents

Some succulents store water in both their roots and stems, these succulents are known as caudiciforms.  The leaves and/or stems of most caudiciforms are deciduous and will be shed during the dry season.  

Caudiciforms survive long dry periods on their large reservoirs of moisture stored in their roots and stems.

Caudiciform succulents (Pachypodium saundersii and Cyphostemma juttae)

Roots

The root systems of many succulents that grow in arid areas are shallow but highly spread out under the soil, this allows the plant to collect moisture from quite a large area.  The roots must be able to collect moisture quickly from sporadic rains and dew; producing new root hairs quickly to collect the moisture before it evaporates does this.

Epiphytes produce aerial roots in dry conditions to collect moisture from the air.

Protection Against Predators:

Succulents employ many ingenious methods to protect themselves from predators;

Poison/Chemical;

Succulents like Adeniums and Euphorbias have a poisonous sap that deters predators.

Taste;

Plants like asclepiads have a foul taste that makes them unpalatable to many predators.

Thorns;

Cacti, Pachypodiums, cartain Euphorbias and many more have thorns to protect themselves from grazing predators.

Camouflage;

Lithops are famous for their mimicry abilities.  These plants imitate the rocks they live amongst, "Living Stones" is an apt name for them.

Underground;

The main part of geophytic succulents occur beneath, this not only protects them from the harsh sun but also hides them away from predators.