|
 BOOK
REVIEWS
Guide to the Aloes of South Africa
By Ben-Erik van Wyk and
Gideon Smith
Published by Briza Publications, Pretoria, South Africa, 1996
$NZ119.95
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
Reviews Main Page
|
