An outstanding Huernia (Huernia praestans)

H. praestans was described by N. E. Brown in 1909 and judging from the name he gave it (praestans = outstanding; pre-eminent) he must have considered it to be something quite special. It is  recorded from a relatively small area in the western part of the Little Karoo (from Montagu to around Ladismith and Vanwyksdorp).
Up to now I only know the species from one slope with a rather dense scrub vegetation  between Hoeko and Ladismith, which is slightly east of the recorded distribution area.

Huernia praestans

H. praestans, east of Ladismith

When I first saw the plants, I thought they belonged to the much better known H. guttata, which occupies a wide area in  the Eastern Cape and the eastern part of the Little Karoo. Its habitats from near Calitzdorp are only 40-50 kms away from the place mentioned above.
The main differences between the two species is the fact that H. guttata only has some bristles in the mouth of the tube, whereas in H. praestans they also occur on the lobes.
All in all little is known of H. praestans and it has been suggested that it is  a hybrid between H. guttata and H. barbata.  The latter has a very wide distribution area, from the Knersvlakte as far as Grahamstown in the Eastern Cape.

Huernia guttata with Duvalia caespitosa

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H. guttata, above (with Duvalia caespitosa) and H. barbata, Mom and Dad?

Warts and all

In a recent post (Cover up, 14th Jan.) I discussed how spines, hairs etc. help succulents conserve water. In some families we also come across plants where the leaves are (partly) covered in warts, papillae or tubercles. Although these are often highly decorative, it seemed likely to me that they would first and foremost serve a useful purpose. After doing a bit of research I came up with some interesting information.
It appears that the presence of these projections on stems or leaves has an advantage for the plants in that the breathing pores are hidden in the lower areas between them. This diminishes transpiration and protects the plants from dehydration.
In the case of warts, there is an additional advantage:  their epidermis is rich in crystals and lies over cells that store up tannin. This combination makes the plant rather unattractive to herbivores.

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Crassula tecta is named after the warts on the leaves (tecta =covered or protected)

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 Crassula corallina v. macrorrhiza (corallina = coral-like)

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In Rhinephyllum graniforme the genus name means file leaf 

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Haworthia scabra is aptly named too (scabra = rough)

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This Astroloba used to be called A. aspera (=rough). The current name A. corrugata has a similar meaning (wrinkled or furrowed)

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Ruschia muricata is rough to the touch and that is exactly what muricata means

In the following two species the names make no reference to things like warts or tubercles, but it is clear that this is not because of lack of these.

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Aloinopsis spathulata

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Stomatium suaveolens

Under cover; ways and means of conserving water

When looking at all those beautiful and unusual forms, colours and textures in succulents, it is easy to think that all thist is there  for our enjoyment.  I’m afraid  that is not the case; most of it is purely functional. For me, instead of  being disappointing, this fact  adds to my pleasure and admiration.  What can be more likeable than things that are both useful and pleasing to the eye? In this post we will have a look at some of the contraptions that succulents use to conserve water.
The one thing that sets succulents apart from all other plants is their ability to store water that they can use during periods when there is no external supply.  Obviously it is not much use to store a lot of water if you do not have the means to conserve it as well. Managing the stored water sparingly, mainly  has to do with reducing transpiration.
The rate at which plants lose water by transpiration is influenced by a number of factors: size and form of the plant, temperature, humidity,  intensity of sunlight, precipitation, wind speed, land slope etc.
On some days the temperature of the soil surface may rise as high as 75 degrees C, but a few centimetres higher up it will usually be much cooler  (up to 40 degrees less ). The two extremes will be separated by a layer of still air.
Comparable layers with gradients of humidity and temperature are found above plant surfaces; they have a great influence on transpiration. These layers are  disturbed or even destroyed by wind.  Because of this, many succulents have a cover of hairs, spines, etc. on the surfaces of their leaves or stems. This helps in producing and protecting these layers.  Such a cover  also gives a certain shade and helps to diminish exposure to strong radiation –especially when it is light in colour.  It has been found that tissue temperatures below spines of the cholla cactus (Opuntia bigelovii) can be reduced by as much as 11 degrees C.

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In this Anacampseros albidiflora, short hairs on the leaves and long bristles between them, cooperate to keep the plant cool

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Pelargonium barklyi is a tuberous plant. Although the leaves are short lived, it is apparently worthwhile to protect them with a cover of hairs     


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Haworthia arachnoidea  gets its name from the spiderweb like cover of hairs. This variety is called scabrispina because the hairs are rough and hard like spines

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In Senecio scaposus the leaves look like covered in felt

Many people think that spines are only there to protect the plants against browsing animals.  In line with what we have discussed here, I think that spines play a certain role in that respect too, but that it is not the only, or even the most important, one.

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 In cases like Othonna euphorbioides (above) and Euphorbia stellispina  -and in many other plants- the spines are actually hardened remains of inflorescences

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Leaf and stem surfaces are often thickened too, or coated with a layer of wax (Senecio stapeliiformis, on top) or cork (Othonna herrei)

 

 

A portrait of the bearded Crassula (C. barbata)

It would be hard to come up with a more apt name for this interesting little gem which is not just beautiful, but also interesting in an ecological sense.
The following pictures show how dramatically the appearance of the plants changes between late autumn and late spring. Please bear in mind that the plants occur in the southern hemisphere, and also that they only grow in the cooler and wetter months (autumn to early spring). They  are almost always found in shade, under shrubs or rocks.

Crassula barbata
Mid May (late autumn)

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Late May

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Early August

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Late September

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Early October

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End of  October (late spring)
Now that summer is approaching, the rosettes have closed to minimize transpiration.  As a result of this, the cover of long hairs at the same time acts as insulation against strong light and desiccating winds.

External water storage in succulents

The great majority of succulents stores water in stems, leaves and/or roots. Some of them however, mainly members of the  vygie family (Aizoaceae) also make use of external storage. They  have an epidermis covered with extremely enlarged and swollen cells (so called bladder cells) that are able to store water. Amazingly up to over 50 % of the total amount of water stored by the leaves can be located in these cells.

The cells have another advantage too: they are so big, that they create windless spaces above the stomata (breathing pores) so that transpiration is reduced. When a plant start suffering from drought stress, the cells collapse. This obstructs the passage of air to the stomata, so that water loss is reduced even further

droscfbrev2010_09_09#189_lznres One of the best known examples is the genus Drosanthemum (“dew flower”)

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Mesembryanthemum guerichianum

In this species (Mesembryanthemum guerichianum), the bladder cells are especially big on the calyx

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Phyllobolus nitidus is named for its shining appearance (nitidus = glossy, polished or shining)

Exactly the same, but different; what post-production can do for your pictures.

A couple of months ago my wife and I were travelling to our farm near Matjiesfontein when we decided to have a short coffee break. As usual, I utilized this opportunity to quickly scan the area. Not far from the road I came across a plant of Cotyledon orbiculata (the beautiful form that used to be called undulata).

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This picture shows my first attempt of photographing the plant.
It is not a bad photo, but neither does it convey the feeling I got when looking at the subject.

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After cropping the picture this is what I got. Much better I thought, but too realistic.

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Cropping in a slightly different way, combined with darkening the picture and enhancing the colours, resulted in this.
It seemed to me I was on the right track, but now the left side of the photo was too busy and distracting.

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I had also made another picture, almost identical to the first one, but taken from a slightly different angle. When I closely compared the two, it became clear that the second one would be the best starting point for the picture I wanted.

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I first treated the picture the same way as in number 3 and the lowered the contrast.
This is the end result, realistic enough to be of botanical value, but at the same time visually stimulating.

Water recycling in succulents

The editor of “Veld & Flora” ( http://www.botanicalsociety.org.za/)  invited me to write an article on succulents for the magazine. It is now ready and will be published in the March issue.
The article is called “Miniature succulents – masters of survival” and highlights some of the intriguing adaptations miniature succulents deploy in order to survive. The following snippet  will give you some idea of what to expect.

A peculiar adaptation is shown by many members of the mesemb family (Aizoaceae), especially the dwarf ones, which are able to recycle water from old leaves to new ones.
As the soil dries out towards the end of the growing period, the older leaves are gradually sacrificed and their water content is translocated to and stored in the younger ones. In this way, all available water reserves are concentrated in the last pair of leaves.
In the end, the dry remnants of the old leaves form a papery sheath acting as a protective layer of insulation for the new ones. When the next rainy period starts, the new pair reaches its final size and bursts through the old skin, ready for action.
It has been found that this adaptation enables plants to survive for about a year without any moisture supply from outside.

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These three pictures of Antimima pygmaea were taken near Matjiesfontein in winter (mid August), spring (early October) and summer (end of January) respectively. At first, it would be hard to believe that it is all one species.