Succulents A new book covers everything gardeners would want to know about these water-wise plants

Once the family to which a plant belongs has been identified, the search for the names of the genus and species becomes much easier. We share a few of our old favourites.

We live in a country where water will only become scarcer and more expensive due to climate change. That is why it makes sense to plant water-wise succulents in your garden. You’ll find everything you need to know in Gideon F Smith and Ben-Erik van Wyk’s new book Garden Succulents.

About 4% of the flowering plants of the world – an estimated 12 500 species – are succulents that use their fleshy leaves, stems and/or roots as an adaptive strategy to overcome brief or prolonged periods of drought.

More than a third of these plants – well over 4 500 species – come from Southern Africa, where it forms about 25% of its flora. This succulent wealth of all shapes, sizes and descriptions is distributed over more than 80 different families and nearly 700 genera, but with a significant concentration in about 15 families.

Other regions with high concentrations of succulents include parts of South America, Mexico and the southern US in the New World, and the Canary Islands and Mediterranean Europe in the Old World.

But what is a succulent?

Defining succulence can be more complicated than it appears to be at first. One definition states, “A succulent is a plant that stores water in its tissues as a mechanism to survive periods of drought in the growing phase (this therefore excludes tuberous and bulbous plants that usually survive drought in the dormant phase)”.

Other scientists prefer the following: “Succulence equates to the storage of usable water in living tissues in one or several plant parts in such a way to allow the plant to be temporarily independent from external water supply but to retain at least some physiological activity.”

Writing an identification guide to all the succulents of the world would be a difficult task, but it does become much easier if we restrict ourselves to succulents commonly grown in gardens. Fortunately, most succulent plant families are so distinctive that they are easily recognised – one need not be a trained botanist or horticulturalist to tell a cactus from a carrion flower or an aloe from an agave. Once you know the differences between the main groups (families and genera), it becomes much easier to identify the plant to species level.

For the layperson, perhaps the most useful subdivision of succulence is according to the plant organ (leaves, stems, roots) that is fleshy. Therefore, reference is typically made to leaf succulents, stem succulents or caudiciform succulents, where the waterstoring tissue is in the stemroot continuum. But other, less conventional plant parts can also be succulent, such as the wiry but fleshy twining inflorescences of the climbing onion

(Bowiea volubilis). Different types of succulence are not mutually exclusive, and plants that combine leaf and stem succulence, for example, are a natural occurrence.

For this purpose, the plants in Gideon F Smith and BenErik van Wyk’s book

Garden Succulents are divided into 10 main plant groups (see page 96).

The eight main families account for more than 80% of succulents, so the ability to recognise these families is a useful first step to identifying species. The reader is encouraged to focus on the critical characteristic of each of the main families. The last two groups – unusual stem succulents and unusual leaf succulents – were created artificially to give wider coverage to plant families that include only one or two succulent members.

1 Sisal family or century plant family (Agavaceae)*

Typical characteristics Leaf succulents; aloe-like plants; fibrous, persistent leaves; flowers usually white or greenish.

* Including Dracaenaceae (dragon tree family) and Nolinaceae (beargrass family)

2 Carrion flower family (Apocynaceae)

Typical characteristics Stem succulents (often lacking leaves); often with milky sap; waxy flowers (often with a strong smell); flowers often adorned with small hairs; seeds with silky seed hairs.

3 Aloe family (Asphodelaceae)

Typical characteristics Leaf succulents; leaves relatively soft, dying back; often with a bitter yellow sap; flowers often red and showy, and borne in a candelabra-shaped inflorescence.

4 Daisy family (Asteraceae)

Typical characteristics Stem or leaf succulents; tiny flowers in dense groups (heads); flowers usually yellow, white or red, and showy; small fruits (achenes) with hairy plumes.

5 Cactus family and prickly pear family (Cactaceae)

Typical characteristics Stem succulents; leaves absent (modified into spines); spines borne in star-shaped groups on felty cushions (areoles); stems without milky sap; flowers large, showy and short-lived.

6 Stone crop family and plakkie family (Crassulaceae)

Typical characteristics Leaf and stem succulents; leaves in symmetrical arrangements; flowers star-shaped or tubular, with prominent nectar glands and four or five petals

(or multiples).

7 Spurge family and milkweed family (Euphorbiaceae)

Typical characteristics Stem succulents; stems with milky sap; flowers usually small and inconspicuous; fruit a small, threevalved capsule. >