Marloth & A.Berger
Name and Classification
Aloe comosa (Marloth & A. Berger) is the botanical name for what is commonly known as Clanwilliam aloe. Although Aloe comosa has always been a part of the genus Aloe, in the past it has been classified as being part of two different families: the Aloaceae or the Liliaceae family. It wasn’t until 2003 that the APG II system placed the genus in the family Asphodelaceae, however some sources still classify aloe in either of the former families.
Aloe comosa inhabits a very small region within the Western Cape province of South Africa. It was discovered in the Olifants River Valley in 1905, north of the town Clanwilliam (hence its common name). The person who discovered Aloe comosa has not been recorded but those that contributed its botanical name were two German botanists, Alwin Berger and Hermann Wilhelm Rudolf Marloth, whom specialized in South African botany and nomenclature of succulent plants. Even though Aloe comosa is indigenous to the Western Cape of South Africa, it is possible for experienced collectors and horticulturalists to maintain their plants outdoors, in Arizona and California for instance, or in a desert climate greenhouse.
Typically, Aloe comosa has thick, succulent blades approximately 2 feet (0.6 metres) long. The leaf surface is glabrous and the curving of the lamina is involute. The morphology of its leaves are simple and have a lanceolate leaf shape that tend to curve towards the tips. The edges of the leaves are entire and are lined with spiny, tooth-like, brown-red thorns. The fleshy blades have a whorled leaf insertion as they emerge from the rosette which sits on top of the erect stem.
Aloe comosa is considered a tree aloe having a single, unbranched stem which may attain heights of approximately 3 meters. As it matures and grows in height, Aloe comosa retains its dry, dead leaves and forms a tangled skirt or beard. Tree aloe bark differs from woody dicot bark in that it doesn’t have a phellogen, which is the meristematic tissue that differentiates into the bark. In essence, aloe bark is actually overlapping, irregular layers of incomplete bark tissues.
A study was published in the science journal Oecologia by W. Bond (1983) on the purpose of retaining dead leaves by several species of tree aloe. Researchers before Bond have set forth studies to try to understand the function of such an adaptation. A few suggestions were that dead-leaf retention protected bare bark from the sun during the day and the cold at night. On the contrary, another researcher believed that the thorny mass of leaves could deter unwanted wild life in search for water, nectar, or seeds. Bond, on the other hand, proposed that dead-leaf retention was selected to provide thick, fire resistant bark in a fire-prone habitat.
Naturally, Aloe comosa follows the typical angiosperm life cycle. Like most South African aloes, Aloe comosa blooms in the summer. Tall inflorescences (flower stems) that can reach 2 meters (6.7 feet) in height branch from the rosette. At the tips of the inflorescences are flower spikes which are composed of many small, tightly compacted flowers. In most cases the color of the flower spikes ranges from rosy-cream to ivory-pink and is pale at the bottom of the spike with a darker pink hue on the upper parts. Pollination is carried out primarily by bees, although it is plausible that some evening moths could be pollinating this species as well.
The seeds are produced in late February and early March of each year in time for the winter rains; the seasonal shift in the southern hemisphere is opposite that of the northern hemisphere. Once the seed capsules turn pale green, they will split and expose their flat, brown seeds. These seeds are enclosed by a thin, transparent membrane which aid in transporting the seeds. In the event of a sufficient breeze, the seeds are dispersed and blown some distance from the parent plant where they usually germinate under the protection of a nurse plant.
The genus Aloe currently consists of over 400 species. A few species of aloe are used to treat minor thermal burns, itching, and sunburn by applying the thick, mucilaginous gel to the skin, but Aloe comosa is not one of those species. Its only apparent uses are a decorative house plant and collector’s item.
- Angiosperm Phylogeny Group (2003). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141: 399-436
- Oliver, Ian. Karoo Desert National Botanical Gardens. July 2006. South African National Biodiversity Institute, South Africa. http://www.plantzafrica.com/plantab/aloecomosa.htm
- Brummitt RK; Powell CE. (1992). Authors of Plant Names. Royal Botanic Gardens, Kew. ISBN 1-84246-085-4.
- Bond, W. “Dead leaves and fire survival in Southern African tree aloes”. Oecologia. Vol. 58, Number 1/ April 1983. pg. 110-114. ISSN 0029-8549 (Print) 1432-1939 (Online)
- Walter C. Holmes & Heather L. White "Aloaceae". in Flora of North America Vol. 26 Page 12, 15, 18, 20, 410. Oxford University Press. Online at EFloras.org.