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Guide to aloesBOOK REVIEWS

Guide to the Aloes of South Africa

By Ben-Erik van Wyk and Gideon Smith
Published by Briza Publications, Pretoria, South Africa, 1996

Reviewed by Dr Philip Simpson

My appetite for Aloe was greatly sharpened by this book. What a genus; such beautiful and interesting plants! There are 125 species in South Africa alone (bigger than the largest genus in New Zealand, Hebe, with 100 species), and still more in neighboring Namibia and Mozambique, northwards through eastern Africa, into Saudi Arabia, and across the sea to the ark and cradle, Madagascar. The "Guide" beautifully illustrates each of the species, mostly in their natural habitat, and describes them in an intentionally "user-friendly" way. A responsible tone is established by the authors' plea not to collect certain species from the wild in an attempt to grow them because their requirements are so specific that the plants will certainly die after a few years in cultivation.

Each species is given a double page. One page presents photographs (with each of the many public sources of colour slides acknowledged), depicting the whole plant, any diagnostic feature of the species, the inflorescence and flowers. The other page describes the species, each in the same way: growth habit, leaves, inflorescence and flowers, the flowering season (generally winter, but sometimes summer), diagnostic features and closely similar species, the range and character of the distribution and habitat, and a map of South Africa, showing National and Provincial borders and with the distribution of each species of Aloe shown as a patch of blue-green. I enjoyed the maps immensely, not only for the geography lesson about South African places that they provided, but, in conjunction with my larger Atlas map of South Africa and the "Guide" text, a quick habitat survey as well. The maps are also helpful because they picture the size and shape of the range of each species (from very large to very small, as would be expected of such a large and diverse genus), whether it is broadly continuous or not (most seem to be), whether species overlap (they appear to, significantly) and the landscape they are part of (coastal sands, lowland bush, dry shrubland, inland grassland, rock outcrops and high altitudes). Are different species that grow together in the same landscape kept apart by habitat, different pollinators, or what?

The species are arranged alphabetically in groups: tree aloes (5 spp), single-stemmed aloes (15 spp; I might have called these "caulescent"), multistemmed aloes (9 spp.), rambling (5 spp), creeping (7 spp), stemless (23 spp), speckled (5 spp), spotted (26 spp), dwarf (6 spp) and grass aloes (24 spp). The authors admit that some of these groups are not natural, in the sense that all the species are closely related, because some merely appear similar, by converging from different evolutionary pathways. The truth is that the identification of aloes is by no means easy in many cases. Some are naturally very variable geographically, individuals of a species vary according to age and condition, there are colour variants and hybridization is common among several species. However, the authors maintain that aloe identification will now be considerably easier. My ability to judge is very limited, but I think their goal has been achieved. For me, though, the main value lies elsewhere.

There are short background sections on aloe-like plants, such as Hawarthia and Kniphofia, medicinal and cosmetic uses (the ancient "aloes" resin, a laxative, and the much more mild Aloe vera gel), conservation (some species are endangered because of over-collecting, and many are naturally very local), and how to propagate aloes and look after them in the garden.

The authors capture an essence about aloes when they describe "The stark beauty of their often strange and inspiring architectures...". They recognise that botanists might want more information about the natural history of the Aloe overall. However, the "Guide" is intended for use primarily for identifying species. It focuses on the question "Which Aloe is that?", and stops sometimes tantalisingly short of the broader picture. The photographs alone achieve most of the story anyway, if you ask the appropriate evolutionary and ecological questions.

Undoubtedly the greatest value for New Zealand readers is the diversity of form, colour and habitat that the photographs and descriptions reveal. There are not many species commonly grown here, and the "Guide" illustrates the wide variety of extremely attractive and interesting plants that we could grow.

The "Guide" starts with the "tree aloes", and opens with A. barberae (formerly A. bainsii), a forest tree that reaches 18m high with a trunk 3m in diameter at the base. This colossal size is equal to or greater than the largest Cabbage Tree (Cordyline australis) in New Zealand , or Joshua Tree (Yucca brevifolia) in California, or Dragon Tree (Dracaena draco) in the Canary Islands, and so joins the select group of the world's largest "tree lilies". Of the endangered tree aloe A. pillansii the author's state "This species leaves a lasting impression on anyone who has seen it in its natural environment. It qualifies as one of the most exceptional botanical features of South Africa. A dichotoma, which features on the hard-back cover, is called the "quiver tree" by some tribes-people, because the hollowed stems were used as quivers. The ethnobotany of Aloe would make a fascinating and rewarding study, given the huge time span and diverse cultural traditions over which people and aloes have interacted.

The "single-stemmed aloes" epitomize "stark beauty", and they exhibit a fascinating range of inflorescence structure and floral arrangement. Many have the familiar candelabra of red racemes. Some have yellow flowers, others Callistemon-like bottle brushes, and a few have tall, unbranched 'spears' like those of the Australian Grass Tree (Xanthorrhoea). The inflorescence of one (A. claviflora) is horizontal, the open flowers displayed for a ground animal . One "exceedingly abundant" species is named A. castenea, for the chestnut-brown nectar it copiously produces. Together, aloes fill a morphologist's dream and a floral ecologist's paradise. What animals, birds, bats, lizards and insects — pollinate these gorgeous structures?

In the "rambling aloes", an almost climbing habit is achieved, to my knowledge an evolutionary first among the "tree lily genera". In the "creeping aloes", the stem grows along the ground, bearing prickly, triangular leaves and inflorescences with more or less round heads of flowers. These two groups are specialized plants. A big group, the "stemless aloes" (not really well named from a structural point of view!), present a range of unique adaptations. A. peglerae forms a ball of incurved, prickly leaves, from which an unusually short and densely flowered raceme emerges. In A. polyphylla, the leaves form a series of perfect spirals, an attracdon that has left the species endangered from over-collection. A. striata is one of the only aloes whose leaves have spineless margins. On the other hand A. melanocantha has fierce looking black spines, not only on the leaf margins but on the undersurface as well.

Many stemless species also have leaves speckled with yellow, white or grey spots, usually uniformly scattered, but sometimes restricted to part of the leaf such as the base, and sometimes becoming organised into a pattern, a feature of A. zebrina, for example.

In the "dwarf aloes" the spots and spines become raised tubercles of hard material, and in these species the leaves are often just a few centimetres long, the rosettes very small, the infiorescences short and the flowers unusually large, almost covering the rosettes of leaves. These seemingly highly evolved aloes are very showey plants and they have been over-collected by gardeners.

The most diminutive species are grouped as "grass aloes" because the leaves are long and narrow, with little or no fleshiness. In some species the individual 'rosettes' are massed together into an almost 'tussock' form. Nearly all the grass aloes have round heads of flowers, sometimes red, some white (A. aibida). In A. kniphofioides the leaf bases expand into an underground bulb. The extreme is A. saundersiae which has a few grassy leaves forming a single rosette, producing a few-flowered inflorescence, and, notably, spindle-shaped, fleshy roots. Aloe is beginning to evolve a focus under the ground. At this highly specialized end of the Aloe range of variation it is impossible not to see other familiar South African genera in some of the characters and trends: hyacinth, grape hyacinth, agapanthus, amaryllis, and scilla, all within the large, diverse order Liliales. The range of form within Aloe from tree to herb, and similarities with these other genera, suggests that Aloe may be a centre for generating evolutionary diversity. There seems to be a sequence from the ancient and large to the modern and small. The "Guide" stimulates such speculation, born from the remarkable diversity that the aloes have achieved. The "Guide" also clearly establishes that there is a serious conservation issue that needs to be respected by those who want to benefit from these unique and wonderful evolutionary creations.

There are also some minor problems with the book. No attempt is made to view Aloe in its entirety — the total number of species, the distribution and the patterns of evolution. I don't think that the last word has been written on the most appropriate groupings of species. There is little about the biology of the plants, the pollination, fruit characters, the seeds and the seedlings, which are pertinent issues for the growers of Aloe. Finally, while the chemical analysis of the leaf sap is mentioned several times, no references are given on this or any other scientific research on Aloe. Perhaps I am unfairly seeking a natural history of Aloe. The references that are given, however, clearly open the door to further reading. The South African Succulent Society's magazine, called "Aloe", is one source that I must check out. The book has stimulated many questions that need to be investigated in order to really appreciate this famous group of plants.

The "Guide" is supported by the National Botanical Institute, and is dedicated to Bosch van Oudtshoorn, the pioneer researcher into the chemistry of aloes. For about $NZ50.00, the pleasure that this book can give, the potentially life-long quest for growing new aloes that it opens up, and the evolutionary and ecological questions it stimulates, it is superb value. My life will certainly never be quite the same.

New Zealand Garden Journal: Journal of the Royal New Zealand Institute of Horticulture 2000 3(1): 22-23

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