Asclepiads are a super-stunning plant family containing over 3000 members. These range from perennial herbaceous plants, woody twining shrubs, stem succulents, lianas and occasionally trees, all belonging to the common “Milk weed”, or botanical “Asclepiadaceae” family.
Today I want to take a look at the range of stem-succulents within this fascinating and somewhat eccentric plant family. Stem succulents are plant life which have adapted over time to survive in their home environments, often resembling species from the Cacti family, though they are only distantly related.
There are many genera and species, but these are relatively rare and few are seen for sale, except from specialist sources. Some of the most likely subjects you will come across include Brachystelma, Ceropegia, Duvalia, Huernia, Stapelia and Orbea, to name just a few.
Members of these fascinating families are natively found in countries with warm, dry climates, such as Africa, the Middle East and Asia. In particular, Africa has two areas where the Stapeliad genus have most diversified, these being the Southern and North Eastern regions. Several species are endemic to Yemen in the Arabian Peninsula and further concentrations are found in a small island called Socotra, located off the Horn of Africa. Several more are found in the dryer areas of Pakistan, Afghanistan, India, Nepal and Myanmar, though only one species is endemic to Europe known as the “Caralluma Europa”. Natively, these are found in the most southern part of the Iberian Peninsula.
Once cut, stems of many species exudes a milky sap substance, hence their common name of “Milk weed”.
The structure of specifically Stapeliad stems are often four angled in a cross-section. There are, however, some species which have 6 or even more than 30 angles per stem, such as those in the Hoodia genus.
Let’s talk Flowers….
The flowers of the Asclepiad stem succulents are both unusual and spectacular, ranging in size from just a few millimetres up to a vast 16 inches in diameter, (40 cm). At the top end of the scale, the Stapelia gigantea species have the largest succulent flowers throughout the entire succulent world.
Regardless of size, all have similar trademark star-shaped corollas, commonly with five points. All the petals of a flower are collectively known as the “corolla”. The Stapeliad genus have more than a few unique and remarkable corolla examples, which we will discuss a little later.
Some genera have fragrant flowers, (though not often of a very pleasant smell). Others have less-offensive odours, but what they all have in common is they use their flower shape and fragrance to achieve the ultimate goal of pollination and therefore, reproduction.
Leaves of the Asclepiad
As a rule, stem succulents generally don’t have leaves – or don’t have what we would call a leaf structure. In most species, the leaf structure has reduced to rudiments which have resulted in often hard, thorn-like structures arranged on bumps or small rounded projections on the surface of their angular form – much like a “wart”.
Asclepiads and Pollination
An extremely interesting and exhaustive subject matter which falls under the heading of “Plant Adaptation” and keeps me hooked for hours. I shall try and keep it short, and apologise in advance if I get carried away!
There are many plant genera which over time have adapted to their environmental needs. A perfect example of this are the Cacti family. These plants have physically adapted to thrive in an environment which is hot, dry and with very limited moisture levels. Their form and complex structure have enabled them to store what little water comes their way, while avoiding excess water losses by opening their stomata at night, only then allowing transpiration to take place. Their tough and often spiky epidermis is proficient at deterring “grazing” animals and because of all of these factors, this plant genus will continue to survive and reproduce.
There are certain plant groups which have taken this adaptation to a new level, especially when it comes to pollination – Stapeliads are one of them and the Orchid genus is another. Although quite unrelated, these two plant groups have developed similar means to attract the same functional pollinator group, resulting in these plants exhibiting unusual traits. This includes an adaption of flower shapes, colour, form and fragrance; all in a bid to attract pollinating insects as they are going about their day, flying around states of Southern Africa.
The Orchid family is well renowned for its impressive diversity of pollination tactics, these include floral mimicry, shelter imitation, rendezvous attraction and sexual deception.
Who ever would have thought it?
Many Asclepiad genera use flies as essential pollinators, these are attracted to an odour resembling dung or rotting flesh which emanates from the flowers. Quite a few of the Stapeliad genus’ flowers also bear a physical resemblance to the rotting carcass of a small animal – this is known as “food-floral mimicry” and is one of the many ways in which the genus attracts flying pollinators through deceptive means.
However, it’s not all bad, we have other species of Asclepiad which smell rather pleasant. Rather than flies, many species use beetles, wasps, bees, moths and butterflies as pollinators – these prefer to have bright coloured flowers and a far more pleasant aroma!
Now that I’ve touched on the subject of pollination with these weird but fascinating floral wonders, I have made a “Top 10” of my favourites and added some media to gain your interest in the Awesome Asclepiad Family.
MY TOP 10 ASCLEPIAD GENERA
A recently discovered genus, first observed in 1999, in the form of a generic epiphyte from the Baynes Mountains in Namibia.
With 22 recognised species, this genus is identified by a disc-shaped corolla and its complex fused gynostegium structure, which is a typical feature in members of the Asclepiadaceae family. This is a colourful species with a distinctive floral shape which purposely leads insects to the nectar cavity to aid pollination. Most widely distributed throughout all of the Southern Duvalias and a close relation of the Heurnia species.
A truly interesting specimen, taken from the Greek “echidna”, meaning “snake or adder” and “opsis”, meaning “looking like”. A reference to its visual appearance of creeping, snake-like stems. Native to Yemen, Omen, Socotra, Eastern Africa, Northern Kenya and Eritrea.
This unique species was discovered by and named after Miss Edith Cole on a plant collecting mission in 1895 to Northern Somalia and is recorded as discovered on 24th March 1895. It is a monotypic genus and native to Ethiopia, Somalia, Kenya, Uganda, Tanzania and Socotra.
The Frerea genus was discovered in Poona, India by N. Dalzell in 1865. He was a super intendant of the Bombay Botanical Gardens and found them growing in large colonies on a bare rock hillside at high altitude of 3000 feet. Dalzell named the species after Sir Henry Bartle Frere, an important promotor of botanical researches throughout India. Unlike other genera, the stems of this fascinating succulent bear true stem leaves.
Native to Namibia, RSA and Botswana, the Larryleachin genus contains few species. Discovered and named after the botanist Larry Leach who studied a range of Euphorbias and Asclepiads throughout RSA and Zimbabwe. The botanist passed in 1996, but his plant genus lives on.
The Orbea genus contains 56 species of clump-forming succulents. Native to RSA and parts of Africa, all plant species have mottled, smooth stems with their tubercles resembling that of a star-fish shape and tapering to a smooth tip.
Discovered in pre-dominant winter rainfall areas of the RSA, the Quaqua genus contains 19 species – these mostly being the old named “Carallumas” species. They have no close relationship to any other Asclepiads.
A genus of low-growing, spineless stem succulents, often regarded as a climax group within the Asclepiad family due to their structurally complex flowers. Sizes range from species to species, some reach less than 2.5 cm in length, whilst others grow to well over 2 metres tall. Native to Africa, particularly parts of Southern Africa.
Native to parts of Southern Africa, the Tavaresia barklyi has possibly the greatest distribution range of all Stapeliads. In growing form, Tavaresia have 6 to 14 angles stems, each with sharp, fine spines. Each tubercle is tipped with a further 3 spines.
The genera listed above are just the tip of the iceberg – there are literally thousands of species within this weird and wonderful Asclepiad family and that doesn’t include the recent hybrid varieties.
I hope you have been inspired by “My Top 10” list and recognised the pure beauty and fascinating qualities of these superb stem succulents.
Look out for my next article with loads of helpful information in the “Asclepiad Grow and Care Guide”, coming soon.