Introduction
In simple terms a "succulent" is a plant that has the ability to store water in specialized tissue for use if water becomes scarce at a later time.
For most people this immediately conjures up thoughts of a dusty, dry desert environment. While this is not out of line as many succulent species are found in
just such an environment, it is not always the case. Succulent plants can be found in just about every environment on the planet, including cold regions, wet environs,
and high altitude. However, plants with at least some degree of succulence are much more common in hot, arid regions, whereas they are typically the exception in other environs.
It is worth noting that there are many other plants that associate with succulent plants in these harsh environments which are not themselves succulents. These plants
have other characteristics which enable them to cope with the extremes of the desert environment. The term used for this type of plant is "xerophyte" - from
the biological term xeric which relates to growing in a dry environment. Note that this term has to do with the environment and not the structure of the plants
to which it is applied. Therefore a "xerophyte" may or may not be a succulent plant. This website, despite the name, is inclusive of these non-succulent xerophytes
for a couple of reasons. One of these reasons is due to the lack of a clear line between succulence and non-succulence. Since all living plants contain some degree of moisture
in their tissues, one must draw a "line in the sand" at some point - artificially designating a given plant as succulent or not. The other primary reason
we include non-succulent xerophytes is a social rather than scientific one. Since this website is built for interests of humans, it caters to the whims of the enthusiast.
Many of these enthusiasts either grow or study xerophytic plants in general, rather than limiting themselves strictly to those with strong succulence. The genus Yucca is an excellent example of a xerophytic plant group that has little actual succulence, but is widely grown by succulent enthusiasts.
As a result, this site contains species that are true succulents, but are not xerophytes. At the same time, there are plants that are xerophytes, but not succulents.
Therefore, a name such as "XerophyteGuide" would be no more fitting than "SucculentGuide" for our purposes. Given that most people are more
familiar with the term succulent vs. xerophyte, the more user-friendly name choice is the former.
Where are the Cacti?
As with the distinction between succulents and xerophytes, we make a separation between cacti and other succulents. It is true that all cacti are succulents and
could therefore be included on a succulent plant website. However, in popular culture, we find most hobbyists, growers, nurserymen, researchers, etc. reference the
cactus family apart from other succulents. For example, the "Cactus and Succulent Society of America" which could just as properly be called the
"Succulent Society of America". As mentioned, the distinctions we make here are strongly influenced by the whims of people, yet there is some
basis for treating the cactus family apart from other succulent plants. Although these reasons are not well-defined and the following is largely my own speculation.
Out of necessity, human populations are small and sparse in arid regions where most succulents grow. In particular, Africa is home to the greater majority of succulent
plant species other than cacti. Conversely, the Southwestern United States has a relatively large population of people living in conjunction with cacti and these plants
are also found commonly throughout Mexico and South America. The "Wild West" stories and movies of these areas have lasting world-wide appeal and often
feature the iconic Saguaro cactus along with other types. This has created an awareness of cactus plants that other succulents did not receive. For political, economic,
and other reasons, there are few movies about South Africa with the great tree Aloes or Euphorbias gracing the silver screen. Very often, if there is a story or
movie based on Africa, the emphasis is on the unique fauna rather than the flora that is found there.
Another reason for the preeminence of cacti among succulent plants is due to the size of the plant family as well as the exclusively succulent nature of the family.
In contrast, other plant families contain far fewer species or may consist of both succulent and non-succulent members. Additionally, the vast majority of cactus
species do have prominent spines, whereas there are many succulents that are spineless or have less dramatic spine coverage. As a result, many hobbyists will
strictly grow the less spiny plants for obvious reasons - thus excluding most cacti. On that same point, there are certainly those who grow cacti for the flowers
and put up with the spines for that reason alone. Cactus flowers certainly stand out among all flowering plants of the world as perhaps the most impressive flowers
of all - if not sharing first place with the Orchids at least. Obviously, that is a matter of opinion.
So it is for these reasons, that the cactus family is treated in it's own right on CactiGuide.com, while all other
succulent and xerophytic plants share a place on SucculentGuide.com
Succulent Types
In general, plants have up to three major components that are easily identified: roots, stems, and leaves. With succulent plants, the structure that contains
the water-storing tissue can be any or all of these components. Root succulence, however is seldom distinguished from stem succulence in this type of discussion and
so these will be treated together herein -leaving us with two major types: stem succulents and leaf succulents.
Stem Succulents
Stem succulents are those plants where the stem of the plant is enlarged to contain the water-storing tissues. These plants may have leaves that are also succulent,
but these are still considered stem succulents, since the stems are the more prominent feature. Other stem succulents may have non-succulent leaves, deciduous leaves,
or no leaves at all.
Within the stem succulents, are those plants that have stems which contain chlorophyll. These typically green stems either take the place of leaves or share with the leaves,
the food-making process necessary in all non-parasitic plants. Non-cactus families that have many examples of stem succulent species are
those of Apocynaceae and Euphorbiaceae.
Other stem succulents do not have chlorophyll in the stems, but depend on leaves to make food. These plants typically have a gray or brown enlarged stem (or tuberous root),
which is a non-woody succulent structure. These plants are commonly referred to as caudiciforms and the enlarged stem or root is called a caudex. Some growers
focus on this specific type of succulent exclusively. They are often grown like a bonsai plant and potted in ways that emphasize or exaggerate the caudex. Plants with
tuberous roots, but otherwise "normal" stems can be deliberately raised above the soil line to show off the large fleshy tuber.
Leaf Succulents
Leaf succulents are plants which typically have small or no stems and enlarged leaves which store water. Plant families such as Agavaceae, Aizoaceae, Aloaceae, and Crassulaceae are predominantly leaf-succulents. Looking through those
examples reveals that a common arrangement of these leaves is that of a a rosette. In the Aizoaceae in particular, however, many species consist of a single pair
of leaves, with no stems. In general, the leaf-succulent plants have no spines or sharp structures, however, as in the Agavaceae, the leaves themselves
terminate in a sharp point. Likewise some Aloe species contain raised points or sharp leaf-tips.
Summary
It is not practical in one page to address the entirety of this subject or consider every exception. Therefore, it is important that the reader keep in mind that
this page is intended as an introduction and not hold to any of the discussion above as a hard and fast rule. As with any science - particularly biological
science, there are always new things to be discovered and unexpected surprises abound. Be sure to visit the Places page for
information about the worldwide distribution of succulent plants. For cultivation and care, the Growing Tips and
Pests and Disease pages are particularly helpful. Even more information of various succulent-related topics can be
found under the Articles section. This is not to mention the further resources under each family, genus, and species
listing along with the Sources, Terminology, and
Discussion forum - we doubt you will exhaust this resource quickly!
Some Succulent Plant Families and their Common Names:
- Agavaceae -Agave
- Aizoaceae -Mesembs/Ice Plant
- Aloaceae -Aloe
- Apocynaceae -Periwinkle
- Cactaceae -Cactus
- Euphorbiaceae
- Fouquieriaceae -Ocotilo
- Piperaceae -Peperomia
- Crassulaceae - Stonecrop
- Welwitschiaceae -Welwitschia
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