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learning about biodiversity Veld & Flora FACTSHEET SUCCULENTS

Liliput and Goliath:Temperature

Read moreDiscover more

about succulents

in these articles

in back issues of

Veld & Flora.

Charting uncertainty: Global climate

change and its implications for our flora

by Guy Midgley et al, vol. 88(2) June 2002

on page 70.

Cliff hangers: What defines a cliff

dwelling succulent plant? by Ernst van

Jaarsveld, vol. 88(4) Dec. 2002 on page 154.

Desert grapes: An epeditition to the remote

reaches of the southern Namib by Ernst van

Jaarsveld, vol. 94(2) June 2008 on p. 82.

Fanfare in the fynbos:Aloe plicatilis, a

unique Western Cape tree aloeby Stephen

Why are so many of the dwarf succulents confined to the winter

rainfall areas and the arborescent (tree-like) species to the

eastern and northern parts of South Africa? Here climate

dictates: a short, cool, moist winter with long, dry,

hot summers often results in dwarfism, whilst warm,

subtropical, moist summers encourage plants to grow

gigantic. Low temperatures during winter demand a

dwarf growth, close to the ground, where they can make

use of the warmth of the soil. During summers they go

into their resting phase. The dwarf mesembs such as

Conophytum , recycle their moisture from the old leaf pair

to the younger leaf pair while retaining the old, dry leaf pair

as a protective covering for the young leaves. Their highly

advanced local seed dispersal ensures they remain within their

habitat which is often on quartz gravel hills.

At the other extreme, high temperatures often result in large barrel-

shaped succulent stemmed plants, such as the Bottle Tree (Pachypodium lealii), Baobab (Adansonia)

and many of the taller Euphorbia species. Growth is cylindrical and tall, getting away from the very

hot ground. The Richtersveld with its winter rainfall, covers a much smaller area (almost four times

smaller) than the Kaokoveld of Namibia with its subtropical summer rain, but the latter is much

poorer in species. Dwarfism allows for specialist adaptation, and the Land of Liliput can thus fit in

many more species than the giants in the Land of Goliath. The dwarf succulents are very popular in

succulent collections as they take up less space, and many of them can be grown indoors.

Succulents can grow in shallow soils, even on bedrock, where there is

little competition from other plants. Most plants simply cannot survive

when the top layer of the soil dries out but succulents, by virtue of

their succulent nature which allows them to survive until the next rain

falls, can. In the Karoo with its low rainfall, many of the shrubs have

deep roots which draw up moisture, whilst the succulents survive

alongside them with their shallow roots and fleshy, moisture storing

nature. Many succulents grow in clayey soil too, as their shallow roots

enable them to cope with the low oxygen content of clay.

Ingenious ways of storing

moisture:WaterWhy are succulents leaves and stems often cylindrical or

round in shape? This is the best surface to volume water

storage ratio! We make use of water tanks which are

cylindrical in shape for storing water. Apart from succ-

ulence many have features for coping with seasonally dry

conditions. Botterboom (Tylecodon) forsake their leaves for

the long dry summers, relying on their green photosynthetic-

active succulent stems. Kobas (Cyphostemma) illustrated in

the centre of this poster, follows the same strategy but loses its

leaves during the winter. (A good example of convergence where

two different plants from different families follow a similar strategy.)

Most mesembs have terete leaves (cylindrical or slightly tapering, without

ridges) orientated towards the sun, thus avoiding the full blast of the suns rays.

All plants transpire to keep cool through their small breathing pores (stomata). How do

succulents avoid too much water loss which could result in desiccation? Some succulents have a

grey or whitish colour which reflects sun light, others have a dense, whitish, hairy skin (epidermis)

such as Senecio haworthii. The Giant Iceplant (Mesembryanthemum barklyi) illustrated on the left

is covered with reflective glittering bladder cells.

An ecosystem is made up of

living organisms that interact

with each other and their

environment. The biotic

components are the living

organisms such as plants,

animals and micro-organisms.

ABOVE:

Xing

Quan from

the Beijing

University

Botanical

Gardens up a Kobas

(Cyphostemmacurrorii)

growing in Omavanda in Namibia.

Coping with adversity Red and green: Light

Cousins, vol. 96(4) Dec. 2010 on p. 164.

Fog and dew in the Succulent Karoo: An

indispensible source of water for arid

Succulent Karoo shrubs by Ignatious

Matimati et al, vol. 96(3) Sept. 2010 on p. 140.

Kleinduimpie Grass: the only succulent

grass in the world by Ernst van Jaarsveld, vol.

95(1) March 2009 on page 19.

The quarzite ridges of Gauteng by Michle

Pfab, vol. 88(2) June 2002 on p. 56.

The remarkable Kaoko Klipblom by Ernst

van Jaarsveld, vol. 93(1) March 2007 on p. 42.

Text and photographs

by Ernst van Jaarsveld

and Caroline Voget.

Download these articles

at http://LABpages.

blogspot.com.

Avoiding predation: Animals

Like all green plants succulents have to trap carbon from

the atmosphere for their normal food production and

growth. Many succulents turn a reddish colour during

dry conditions. This is the result of a pigment, antho-

cyanin, which is the plants solution to slowing down

photosynthesis and thus dimming the suns bright

rays. Succulents thus put their foot on the brakes

when moisture becomes scarce. This reddish colour

is not confined to succulents, and you can often see it

in young leaves (for protecting the young, vulnerable

tissue) or in deciduous trees and fruit which ripens (a

sign that the fruits are ripe).

Many succulents keep their breathing pores closed during

dry, sunny conditions, only opening them during the night. How

do they manage to photosynthesize, which requires CO2? During the

night, the plants accumulate organic acids to which carbon is bound, which during the day, are

broken down again and the CO2 released making it available without having to loose moisture via

their breathing pores. This is known as Crassulacean Acid Metabolism (CAM).

Not all succulents grow in full sun. Most of the smaller species grow on south-facing slopes or

below Karoo shrubs that provide protection from the sun.

Putting down roots: Soil

The high water content of succulent plants makes them vulnerable

to herbivores, particularly the larger mammals. There are various

ways they avoid predation. The big and bold succulent plants

such as Aloe feroxand most euphorbias are spiny, and any

animal would think twice before taking them on. They also

have another trick up their sleeve chemicals. Aloes are

extremely bitter, and euphorbias have a with milky latex

that can damage eyes or burn skin.

Another clever strategy some follow is to blend in with

their background (camouflage). This group is usually small

and humble; some resemble stones (stone plants such as

Lithops and Pleiospilos), others simply have mottled green

leaves (Gasteria and Senecio articulatus) which grow below

shrubs and are thus difficult to see. There is also a large group of

dwarf succulents that rely on other plants for their defence. They hide

below spiny shrubs (nurse plants) and are thus well adapted to grow in shade

which is why they make such good indoor plants.

Some, like the large and very palatable Spekboom ( Portulacaria afra) however, are quite without any

defence. They make use of a different strategy altogether passive resistance! Any bit of vegetative

material that falls to the ground when broken off the parent plant, immediately roots and forms a new

plant. Karkei (Crassula ovata), Klein-karkai (C. tetragona), Ox-tongue (Gasteria), Adromischus and many

others have also evolved this strategy, turning predation into procreation.

Succulent plant diversity in South Africas low rainfall regions is exceptionally

rich and fascinating. Spanning many different families, they vary from

miniature tufted plants such as Conophytum to the big and bold Baobab,

the worlds largest succulent. Succulents are highly specialized and

evolutionarily advanced in comparison to plants from high rainfall regions.

Lets explore some of the ways they cope in their low rainfall ecosystems.

Abiotic components of an

ecosystem are the non-

living components that

affect plants and animals.

They include temperature,

water, light and soil as well as

altitude and aspect.

VELD&FLORA | MARCH 201224 MARCH 2012 | VELD&FLORA 25