Thursday, June 25, 2015

South Africa 8. Succulent Paradise

Euphorbia stellospina remarkably mimics the
growth form of cacti native to the Americas.  One
cllue is the forked spines found only in Euphorbia.
Northward and inward from South Africa's west coast, it becomes increasingly arid. These southern African deserts are home to the greatest collection of succulent plants on the Earth.  Succulents are plants that store large quantities of water in their soft tissues, allowing them to remain active during prolonged dry seasons.  Other desert plants become dormant, fulfilling their life cycles during the brief period after a rainstorm, or have other specialized means of survival, such as long taproots that reach underground water supplies.

One first thinks of cacti when the word succulent comes up, and they are almost completely confined to the Americas.  None occur in southern Africa.  With some 1500 species of cacti, one might think the Americas would have the greatest collection of succulents.  We can add to their numbers some 200 species of Agave and many members of the Crassulaceae, but in Africa, the role of succulent is filled with members of an even greater variety of families.

Hoodia rushii (Asclepiadaceae) is a cactus-like
member of the stapeliad group. This is the genus
from which a controversial appetite-suppressant
is obtained. [Note: the Asclepiadaceae is combined 
with the Apocynaceae in some systems.]
One can categorize most succulents as either stem succulents (cactus-like) or leaf succulents (like Agave or Sedum). The most numerous stem succulents in Africa are in the genus Euphorbia  and the stapeliad group of the Milkweed family (Asclepiadaceae) or ), but there are also some in the Apocynaceae Pachypodium), Asteraceae, Grape, and most improbably, the Passion flower (Adenia) and Geranium (Pelargonium) families, as well. African leaf succulents include many in the Crassulaceae, the genus Aloe and its relatives, and the ice plant family, Aizoaceae.
Pachypodium namaquensis (Apocynaceae) is
related to Nerium oleander, periwinkle, and
confederate jasmine..

It's hard to put a number to this collection, but I believe it exceeds the number of succulents in the new world.  For example, the stapeliads consist of 29 genera, each with a number of species. The genus Stapelia alone has 55 species.  Euphorbia consists of over 2000 species worldwide, and includes tiny herbs, trees, and about 1000 cactus-like succulents in Africa.  The genus Aloe, all succulent and mostly native to Africa consist of  500 species, the Crassulaceae contains several hundred here, and so the number builds up.  Aizoaceae, a family with succulent leaves contains 1782 species in Africa.

So I rest my case for southern Africa possessing the greatest treasure chest of succulents, and invite you to enjoy the pictures.
Pelargonium spinosum is a spiny, succulent
 member of the large genus featured earlier in this

This Agyroderma (Aizoaceae), like the related genus Lithops,
typically maintain only two functional leaves that are half-
buried in the rocky soil, and have the common name of
living stones. 

A stop at the Kokerboom Nursery, gave us a great preview of
the native succulents of South Africa.
Tylecodon paniculatus (Crassulaceae) is a
common desert shrub in southern Africa.
The attractive blossoms of Tylecodon paniculatus.
This planter box features living stones and other members
of the Aizoaceae.

Euphorbia mauritanica has slender succulent stems, and
leaves during the rainy season.

Euphorbia tuberculata; one of many cactus-like
species in this genus.

Orbea ciliata is a cactus-like member of the stapeliad
group of the Asclepiadaceae.

Sarcocaulon crassicaule is a succulent member of the Geraniaceae.
Aloe erinacea; a small, spiny member of
this large African genus.

Larryleachia cactiformis, a stapeliad with small, dark flowers.
Aloe pitchifolia at the Kokerboom Nursery.

Aloe framesii

Aloe chabaudii

Trichocaulon flavum, another stapeliad; note the milkweed-like
follicles on the stem on the right.

Eupohrbia clandetina; another succulent with
temporary leaves.

Wild Aloe dichotoma trees on a rocky hillside.

The bark of Aloe dichotoma forms patches of different color.

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