Aloe ferox Archives - enjoysucculents

Of all the problems succulents face in nature, the main one is the scarcity of water.
In most dry areas the rainfall is unpredictable, with long periods of drought. For at least part of the year, this goes hand in hand with a low humidity (in daytime often lower than 20%), which in combination with high temperatures leads to high evapotranspiration.
Even when there is rain, only part of the water becomes available to plants. The more water comes down in one go, the more runs off or otherwise disappears, especially in rocky and sandy soils.
When water becomes available, succulents must be able to collect it as quickly and thoroughly as possible and they have developed a number of adaptations for that purpose.
Most of them have a shallow rooting system, mainly at a depth between 5 and 15 cm and often extending 10-20 m away from the plant.
A disadvantage of such a root system is that the topsoil may become very hot (70° C or higher) but it allows the plants to absorb even small quantities of rain, dew or mist. The roots often end underneath stones, where they form dense mats. Stones condense dew and mist and collect the water at their base and in crevices; they also protect the roots against drying out.

Shortly before dawn, plants too often reach such low temperatures that a substantial amount of dew accumulates on their surface. (Argyroderma delaetii and Cephalophyllum curtophyllum)

In the dry season many succulents lose their fine roots, but even a little bit of moisture will quickly cause the growth of very fine so-called rain rootlets, which will then absorb nearly all the available moisture.
When enough water becomes available, succulents may take up so much that they literally burst.

A plant such as this Augea capensis may increase its weight several times after rain

This plant of-Fenestraria rhopalophylla is just a few cm across but has roots which may cover up to two m2. Fenestraria occurs in the mist zone on the coast of northern South Africa and southern Namibia, where the sea mist is the main source of water.

Because dew and mist are often more reliable than rainfall, they are important sources of moisture for other plants as well. These plants of Aloe ferox grow not far inland from the south coast in South Africa and regularly receive mist rolling in from the sea.

The large leaves of this Aloe microstigma cool down sufficiently at night to collect dew. In many places dew may be the main or even only source of water for months.

Mesembryanthemum ( Prenia) sladenianum has spoon-shaped leaves that are perfect for condensing dew and mist

At night, protuberances such as spine tips, hairs, papillae, bladder cells, thorns and spines will become cooler than the rest of the plants and the surrounding air, so that dew condenses at them and is channelled to the roots.
In certain cases, the water can be absorbed directly by these appendages.

Crassula sericea var. velutina uses inflatable epidermis cells

The white scales of this Avonia papyracea are so-called stipules, outgrowths at the base of the leaves. In this case they are much bigger than the leaves themselves and protect these against sun and wind. At the same time these stipules are able to trap water.

Trichodiadema marlothii Back in 1908, Rudolf Marloth in his famous book Das Kapland, reported the following on plants of this genus: “As soon as one puts a drop of water on a hair at the tip of a shrivelled leaf, the cells suck it up and in a short while the leaf is plump again”.

The term hydathodes is normally used for structures that are in control of guttation (loss of water in the form of drops from the margins of leaves).
The hydathodes that are found in nearly all species of the genus Crassula perform the opposite function: taking up condensed water and atmospheric water vapour. They are arranged in one or two rows along the margin and/or they are distributed over the surface of the leaf. and are often surrounded by trichomes (hair-like growths) which are supposed to assist in trapping water.

Crass. nudicaulis var. platyphylla

In some plants, only the young leaves have hairs, whereas the older ones are smooth. The first of the two pictures above shows a young plant of Tylecodon paniculatus. In the second picture a mature plant of the same species is accompanied by a plant of T. wallichii (on the left). These species sometimes hybridise in the wild.

With their many thin stems, broom-like Euphorbias such as this E. burmannii do not look very well equipped for dry conditions. It seems however that they are rather effective in collecting condensed dew and mist and channelling this moisture to their roots.

The same applies to other thin stemmed plants such as this Crassula muscosa v. obtusifolia

For other posts in this series click here.

When looking up descriptions of plants, one often comes across pieces of botanical jargon, terms that are either used only in botany or have a specific meaning there. Of course there are books and internet sites where one can find the meaning of these terms, but the explanations are often in arcane language and usually there are no illustrations. (“And what is the use of a book,” thought Alice, “without pictures or conversation?” ― Lewis Carroll, Alice’s Adventures in Wonderland). In 1993 the British Cactus and Succulent Society published a booklet called “Glossary of botanical terms with special reference to Succulent Plants”, compiled by Urs Eggli. This useful publication is now out of print, but second hand copies can be found on the internet. Unfortunately -like in other publications of this kind- the explanations are accompanied by a line drawing at best, so that it is not always easy to relate the information to a real plant. When thinking about this, I wondered if it might not be a good idea to publish a post occasionally explaining some botanical term and using photos to show what is meant.

To kick off, let’s start with a type of inflorescence that is very common in the Aloaceae family (Aloe, Astroloba, Gasteria, Haworthia, Poellnitzia). It is called a raceme, in which inflorescence the main axis does not end in a flower at the top and the flowers start to open from the bottom upwards. Below left you see a drawing of this. On the right you see a spike, which is a raceme in which the separate flowers have no stalks.

The 3 pictures below show racemes of (from top to bottom) Aloe ferox, Astroloba bullulata and Ornithogalum juncifolium.

Tag: Aloe ferox

The survival of the fattest: Collecting water

Coming to terms