Published in AVONIA – Journal der Fachgesellschaft andere Sukkulenten 20:3 (2002) and updated in January 2007

Ill. 1: rough epidermis of a young leaf.

Friederike Hübner und Ulrich Tränkle

Summery

In this short article the authors supply details about the ecology and habitat of Aloe asperifolia, with an emphasis on the climatic situation. The pictures illustrate the habitat and the location where the species are growing. They also provide some tips for the greenhouse cultivation.

Ill. 2: typical and relatively wet location at the base of a rock.

Introduction

On several field work trips to Namibia we managed to observe Aloe Asperifolia in situ - a species rarely found in cultivation. Aloe asperifolia has a large natural range from Walsfishbay in the South up to the  southern Kaoko field. We frequently found it in the very meagre and wide lichen fields of the outer central Namib, growing beneath the black Dolorit ridges (a special kind of basalt) in the surroundings of Swakopmund.

The plant

The leaves of Aloe asperifolia are of a vivid grey-green, rather wide at the base, displaying a yellowish fringe and rich yellow, later brownish spines. It carries the name Asperifolia due to their rough surface reminiscent of sandpaper (see ill. 1). Young plants appear to have no stem, older ones however exhibit a typical short creeping stem, the eldest part of which is usually abraded by sand and water leaving it charcoal coloured and no leaveless. Most of the stems we found were up to 50 cm long, only few were considerable longer, having a length of more than 1 m.

The Cape Dutch name reflects the peculiarity in the way the plant grows: its Cape Dutch name is "kraalaalwyn" reminiscent of the traditional circular arrangement of houses in native villages. They are also called "heksekringe" (with rings) as the German name for the fairy rings of mushrooms in Northern Europe. Big rings of aloe can be seen in the sandy slack of the lowlands, which can be found for instance in the area of occurrence of Weltwitschia mirabilis. The younger and also very sturdy plants however grow between the black boulders of the Dolorit ridges (ill. 2 and ill. 3) where there is a much better availability of water throughout the year than the climatic diagrams show. Sarcocaulon species, namely Sarcocaulon marlothii and Sarcocaulon salmoniflora as well as Larryleachia marlothii, Hoodia pedicellata and Hoodia currorii, Pelargonium klinghardense settle right next to the lichen covered rocks.

Ill. 3: Flowering Aloe asperifolia between the rocks of a dolorit ridge.

The inflorescence of the Aloe asperifolia angularly slants sidewards until it almost reaches a lying position. It is very loosely equipped with small, approximatly 3 cm long, reddish to rose-coloured blossoms. They bloom predominantly in March and April, but this is subject to change in years with rain. Court (1991) describes them as barely spectacular. Yet, bearing in mind that there are no other blooming plants no matter how small to be found within a distance of 200 m no matter how small, Aloe asperifolia is a unique beauty.

The climate

As far as the climate is concerned, this part of the Namib is very dry, as the climate chart clearly seems to indicate (ill. 4).  But then again, we are used to measuring climate by data from a standard weather station.  There are only 2 to 5 rainfalls per century heavy enough for  the desert to be completely green. The normal average precipitation rate is 15 mm per year, at an average annual temperature of 15.3 °C. That is what we call extremely arid climate. The standardised measuring instruments of a normal metereologic station do not account for amount of water supplied to certain habitats by air moisture or fog. The coastal city of Swakopmund has about 200 foggy days or rather nights per year.

Ill. 4: Climatic chart of Swakopmund (from Walter/Breckle 1999, modified).

Yet, there are not only the wafts of mist caused by the cold Benguela stream, billowing from relatively high above the coast into the countryside, which account for the impression of an almost chilly climate during daytime. At night the temperatures even drop below a comfortable degree. Whoever has got the chance should spend a few nights out in the open in a tent 20-30 km off the coast in the months from August to October. With a little luck you may encounter such dense fog you won't be able to find the tent any more (some remains of such fog can be seen on ill. 5). The droplets of the fog can easily be seen by torchlight and precipitate faster than anywhere else on the black Dolorit ridges as they cool down faster than their surroundings at night. During the day however the shadows of the rocks protect the soil from heating up and hence from dehydration. The plants growing there thus receive an almost constant supply of water, which would not be expected looking at the climate chart.

This phenomenon has also been recorded by Walter in the thirties and seventies of the last century.

Ill. 5: Remainders of fog in the lowlands near Mt. Rössing, Swakopmund in early morning light)

Cultivation

In culture Aloe asperifolia require regular doses of water and of fertilizer. Even rather small offshoots soon bend sideways and can't be kept from growing in a creeping way, not even by using stones or canes. We keep our plants in sandy cactus substrate with a 20% of humus share in the greenhouse. They do not necessarily need the sunniest of places, but then again, too little solarisation quickly leads to weak colouration and prolonged growth.

The 12 year-old seedlings grow rather slowly. The species best suits a greenhouse ground patch, since then the typical creeping stem can develop on the ground. Unfortunately, Aloe Asperifolia cannot be kept from growing at an increased rate during the winter. In years with a lot of sunshine this is no problem. If there are however weeklong periods of grey and cloudy weather, the plant suffers from lack of light. This can be helped by installing artificial lighting for the plant.

The structured, light grey-green surface of the thickly succulent, large leaves and the contrast to the yellow little sheet teeth account for a great interest of enthusiasts in this plant. Our plant flowered in 2004, as the summer of 2003 was extremely hot and sunny, when it also split up and developed two stems - but this was the only occasion on which it flowered within 17 years.

Ill. 6: 12-year-old seedling. The creeping stem is about 20 cm long.

Literatur

Walter, H.; Breckle, S. (2002): Walter's Vegetation of the Earth. 547 S.

Walter, H.; Breckle, S. (1999): Vegetation und Klimazonen. 7. Auflage. 544. S.

Craven, P.; Marais, C. (1986): Namib Flora - von Swakopmund zur großen Welwitschia über Goanikontes. 126 S. (Beautiful little book with lots of drawings; it is worthwhile to recapitulate the route described there, as many different habitats in the Namib will then be visited; it is however no academic book)

Court, D. (1981 new edition 2001): Succulent Flora of Southern Africa. 224 S. (Supplies a a serviceable overview on succulents in southern Africa; contains lots of photos with only brief descriptions, certain species are missing completely in the new edition)