Introduction to Succulent Plant Groups
Succulent plants number around ten thousand species and display an extraordinary variety of growth patterns. They can be divided into
three basic groups based on their water-storing structures: stem succulents, leaf succulents, and caudiciforms. Let us now examine
each of these three groups and some of the larger and more conspicuous succulent plant families.
Stem succulents, as the name implies, are those plants that store water in fleshy stems. The Cactus family is by far the largest group
and includes over one quarter of all succulent plant species. However, many people differentiate the true cactus from other "succulents" because of the
large number of cactus species and the preponderance of spines. The majority of non-cactus succulents do not have the heavy armor of spines or thorns for which
the cactus family is renowned.
One of the more prominent succulent plant families is Euphorbiaceae. This family includes the
genera, Euphorbia, Jatropha,
Monadenium, and Pedilanthus. Euphorbia is an
extremely large genus of around two thousand species, but not all of these are succulents. Just under half the species can be considered "succulents"
or at least "xerophytes". Many are popular houseplants and are the most frequently confused with true cacti by the novice. This mistake is
understandable, however as they are often referred to as "Old World Cacti". Despite these similarities they are have many differences -- break the
stem of a Euphorbia and a potentially irritating white sap will ooze out. The genus Euphorbia occurs in mainly in Africa - especially the most cactus-like
species, but the genus is found in all around the world.
Asclepiadaceae is another sizeable group of stem succulents includes the genera Brachystelma, Carulluma,
Ceropegia, Duvalia, Echidnopsis, Frerea, Hoodia,
Orbea, Piranthus, Pseudolithos,
Stapelia, and Trichocaulon. Many of the genera in this family are prized by collectors for their odd
shapes and flowers. A large number of species have flowers which smell like carrion to attract fly pollinators. Growers often refer to this group in general as "Stapeliads".
Leaf succulents, as might be expected, store water in fleshy leaves. Aizoaceae, formerly known as Mesembryanthemaceae,
or "mesembs" for short, is a large group of plants consisting of around 120 genera that include among others, Aloinopsis,
Argyroderma, Carpobrotus, Cheiridopsis,
Conophytum, Drosanthemum, Faucaria,
Fenestraria, Frithia, Gibbaeum,
Lampranthus, Lithops, Nananthus,
Ruschia, Titanopsis, and Trichodiadema.
Some genera such as Carpobrotus, better known as "Ice Plant", have been used as ground cover in arid areas such as along freeways in California where they
have become a noxious weed. Another more popular group is Lithops, affectionately called "Stone Plants" or "Living Stones", are a perennial favorite
among collectors. Most of these mesembs originate in Africa - particularily Southern Africa and wome have been in cultivation for several hundred years.
Aspodeliceae is a large group of leafy succulents that include genera such as Aloe, Astroloba,
Gasteria, and Haworthia. This group of popular succulents
is grown largely for their beautiful foliage although some have quite colorful inflorescense. Most people are familiar with the popular
Aloe vera, a medicinal plant that is easily grown as a houseplant. However, this genus also includes many large species
that are used in landscaping such as the tree-like Aloe dichotoma or the huge, robust clumps of
Aloe arborescens. Many species of Haworthia and Gasteria are popular windowsill plants
and were first cultivated in Europe over three hundred years ago.
Crassulaceae is another huge family of plant genera including Adromischus,
Aichryson, Aeonium, Cotyledon,
Crassula, Dudleya, Echeveria,
Greenovia, Kalanchoe, Pachyphytum,
Sedum, Sempervivum, and Tylecodon. Many of the genera in this family are
household favorites for their lovely geometric leaf patterns and showy flowers. Many, such as Aeonium, are commonly used in landscaping in warmer climes while the
Sedum and Sempervivum (Hen and Chicks) are among the hardiest of succulent plants.
Caudiciforms are succulents with an enlarged stem base known as a caudex. The term "caudiciform" is less a scientific designation than an aesthetic one.
Asclepiadaceae and Euphorbiaceae include a wide variety of caudiciform species, but caudiciforms range across many plant families. Some popular caudiciform
genera include Adenium, Fouquieria, Dracaena,
and Pelargonum, to name a few.
Author: John Balcom/Daiv Freeman