Travel Reference
In-Depth Information
PLANTS OF DRY HABITATS
Unlikeanimals,plantscannotescapeharshenvironments.TheplantsofMadagascar's
dry southwest have therefore had to adapt to tolerate strong sunlight, high temperat-
ures and - most restrictive of all - desiccation. These high demands have produced
unusual-looking and fascinating plant species called
xerophytes
.
Allxerophyteshavedeeprootsystemstoacquirewhatlittlewaterthereisavailable.
Their leaves are usually small and covered in hairs, and much of their photosynthesis
is done by the green stems. This design lowers the surface area of the plant and traps
still air adjacent to the leaf, reducing water loss - the key aim. In addition to desicca-
tion, overheating isas much aproblem forplants as it is foranimals. Xerophytes have
thereforeevolvedvarioustechniquestominimise heating:usuallytheyhavetheirnar-
rowest edge facing the sun and they often add grey pigments to their leaves to deflect
the harsh rays of midday.
The most extreme adaptations for a dry life are to be seen in the
succulents
. This
general term describes all xerophytes which store water in their waxy leaves, roots or
stems. Water is a valuable commodity in a dry habitat, and one that must be protec-
ted from thirsty grazers, so succulents usually employ toxins or spines as a defence.
This is evident in many of the island's spectacular plants, not least the octopus trees
(
Didierea
) of the spiny forest.
Aloe
is a genus containing about 450 species occurring in southern and eastern Africa and
Madagascar. Over a hundred are recognised in Madagascar but there are distinct differen-
ces between African and Malagasy species. Madagascar does not have any grass aloes or
spotted aloes, but has numerous species which differ markedly from those growing else-
where. Even though aloes are known as low-growing plants, some species have stems to
raisetheirbroadfoliageabovetheground.Thelargestaloeshavestocky3mstemscovered
inuntidydeadscaleswhichsporthugesucculentleavesand,inJuneandJuly,alargeredin-
florescence.
A. divaricata
is a fast-growing species common in the southwest. Its single or
branchedstemsare2-6mlongwithnarrowblue-greyleavesandred-brownmarginalteeth,
scattered along the whole length. Highly branched inflorescences of up to 1m bear coral-
red flowers.
A. suzannae
is unique among aloes in being a night-bloomer; flowers open
before midnight and close the following morning. Flowers (which only appear on plants at
least ten years old) are pollinated by the souimanga sunbird and Madagascar white-eye as
well as by bats and mouse lemurs.
Kalanchoe
contains 143 species of succulent perennials distributed through Africa, Mad-
agascar, Arabia and Asia - with 63 occurring in Madagascar. The most well known is the
panda plant (
Kalanchoe tomentosa
), a shrub with dense rosettes. The species are highly
