Caudex


This very rare Asclepiad and one of only two endemic species from the Dhofar region of Oman, the other being a Dhofaria macleishii (of the Capparaceae family). It is extremely drought tolerant and slow growing. It is an ideal plant for a small collection as it grows very slowly. I have had mine for about 3-4 years now and it has only grown by 4 centimeters in that period. Not suprisingly, it does appreciate warm temperatures, at least 20°C. Despite the fact that it grows in the full sun in the wild, my experience with this plant has shown that it can be grown in the shade without any problem.

It will also flower well, producing up to ten flowers successively in October-November. The flowers are about half a centimeter in diameter and stay open for two or three days. On my plant, they are produced on the new growth at the end of the stem, but in older plants with more growth, they grow in the leaf axils. You can see a picture of a dried specimen here. The few leaves the plant produces at the end of the stem, drop off before the flowers appear. The leaves you see growing in the picture are from a different plant, a Dorstenia foetida.

The plant was named Cibirhiza dhofarensis by Peter Bruyns, but is also known as Cibirhiza dhofarica. Cibirhizas are closely related to Fockea, a well-known species of that genus being Fockea edulis. The tuber of the Cibirhiza is supposed to be edible, but I have not tried it, because I only have one plant and it would be a shame to destroy it.

Cibirhiza dhofarensis

Cibirhiza dhofarensis


Cibirhiza dhofarensis

Cibirhiza dhofarensis

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Most people know of the tomato tree, but there is also a plant called the cucumber tree, which is endemic on the island of Socotra which belongs to Yemen, but lies closer to Somalia than to the Arabian Peninsula. It was discovered by Sir Isaac Bayley Balfour in 1882. It is extremely rare in cultivation with very few nurseries offering it for sale. It is a monotypic genus in the family of Cucurbitaceae and the only tree in the family, the rest being climbers. The temperature on the island is always more than 20°C, also at night, therefore this plant requires a high temperature in the greenhouse to grow. It can survive at lower temperatures, 15°C minimum, but it won’t grow well. It also prefers bright light, but will tolerate some shade. It can take a lot more water in the growing season, but be careful not to overwater it in the winter. If you keep the winter temperatures high enough (20°C or more), the plant will keep its green leaves, but will drop most of them them when kept cool (15°C). It can grow to a height of six metres, producing a whitish bark which contrast with the green leaves.
The flowers are produced after about five years from seed; the flowers are yellow as with most Cucurbitaceae and unisexual and monoecious (growing on the same plant). The fruit is orange, but fairly small and mainly eaten by the sheep and goats on the island. Traditionally, it is also used for medicine.
Propagation is mainly from seed, but a few exeperiments that I have done prove that it is possible to propagate the plant from cuttings. One needs tip-cuttings put it a high humidity propagation unit, so that the cuttings will not dry out. I do not yet know, however, if the plants will form a caudex if grown from cuttings. Experiments are ongoing.

For a more complete description of this interesting plant, see here.

Dendrosicyos socotrana

Dendrosicyos socotrana


 

This perennial climber comes originally from South-America, but has now spread over most of the the warmer parts of the world. It is also known as Madeira or Potato vine. Growers in Europe have this as a collector’s plant in their greenhouse, whereas in the warmer parts of the world, they are trying to get rid of it. In some countries is has even become an invasive weed that is difficult to eradicate, because it is almost impossible to get rid of all the small tubercles. When you dig up the plant, the small tubercles that have formed on the stems fall off very easily.
Cutting the stems and leaving the branches lying around does not help to kill the plant, because there is enough energy left in the stems to produce the small tubers. If you really want to get rid off the plant, you need to burn the stems (make sure you gather up all the tubercles that have fallen off) or poison the plant with Glyphosate. You need to do the latter by scraping the bark and putting the poison on the wound so it will be taken into the plant. A bit harsh, but it is the only way unless you happen to live in a country where the temperatures fall below zero, because they cannot take any frost.
Anredera can grow to up to 9 metres long and has bright green heart-shaped leaves. In the autumn, it produces large numbers of small fragrant flowers in racemes. It can grow in semi-shade or full sun and can take a lot of drought. It is propagated mostly by tubercles, rarely by seed. Because it is such a rampant grower, it can be cut back almost to the tuber and it will come back and flower the following year – an ideal beginners plant.

Anredera cordifolia

Anredera cordifolia


 
Anredera cordifolia raceme

Anredera cordifolia raceme


 
Anredera cordifolia tubercle

Anredera cordifolia tubercle

A good plant for cactus collectors, because in the winter it can take low temperatures (even a bit of frost) if kept dry. It comes from the Eastern Cape in South Africa and the tuber can grow to a height of 25-30 cm. The branches that grow on top of the tuber can, if they get too large, be cut back. The flowers develop all over the branches, so you do not lose them if you cut the top bits of the branches off. The flowers are similar in shape to those of Adenium obesum, but smaller. The pollinator is probably a moth as the depth of the flower excludes other pollinating insects. When pollinated successfully, twin seed horns will appear which grow to a length of about 5 cm, containing up to 30-40 seeds. The seed has a parachute on the end enabling it to be carried away to a new area to grow. You can tell the difference between an Adenium seed and a Pachypodium seed, because the latter has just one parachute, while Adeniums have two. It is important to remember that the seed from both these species must be sown fairly quickly after collection, because they have a short ‘shelf-life’. It can be kept for a maximum of one year, but the germination will only be about 10%, if you’re lucky. The fresher the seed, the better the germination, possibly up to 100% if sown the first few days after collection.
Pachypodium bispinosum is virtually identical to Pachypodium succulentum when not in flower. To tell them apart, you need to see the flowers; the ones from the succulentum are flatter. In the wild, their localities overlap a little bit, but there is hardly any cross-pollination, probably because the pollination needs different insects.

Pachypodium bispinosum caudex

Pachypodium bispinosum caudex


Pachypodium bispinosum flower

Pachypodium bispinosum flower

This caudiciform species comes from China and is very easy to grow. It can be grown outside in the garden in the summer, or just as easily in a pot. It can take a little bit of frost, especially if the soil is very sandy and well-drained. If you do not have this sort of soil, it is advisable to take them out before the winter and treat them as you would Dahlia tubers. The tubers are potted up in spring and can be either buried completely or half above ground so you can still see the tuber (see photo below). The plant prefers cool conditions (10-18°C); if the temperatures are too high (for instance, if you keep them in a greenhouse where the day temperatures get above 25°C), the flowers can become misformed.
The flowering period is from May to August and the colour of the flowers can be pink or white; the variety show in the picture is ‘Snowtop’. This genus does also have a yellow-flowered species, Incarvillea lutea, but that is a very rare sort.
Seed collected one year can be sown the following spring. The plant will form a tuber that first year and will flower the following year, so two years after collecting the seed. It is a relatively pest-free plant, but watch out for greenfly.

Incarvillea delavayii Snowtop tuber


Incarvillea delavayii Snowtop flower

Jatropha podagrica is native in South-America where it can grow into a large flowering shrub. It is now found in Africa and Asia as well, because this plant is propagated in nurseries and due to the springing of the seed when ripe the plant has escaped from the nurseries into the wild where it can establish itself. Due to the poisonous nature of the sap, there are few creatures that will attack it. Jatrophas belong to the Euphorbiaceae which can be seen by the seedpod that is divided into three sections, each containing one seed.
It is a plant that requires warmth; it will die if the temperature drops to 5°C for a prolonged period. The ideal temperature is at least 15°C. The plant is very easy to cultivate as long as the temperature is high enough, not requiring a specific type of soil; it can be grown in the full sun or above the central heating with little water. It can remain in this position all the year round, not requiring a colder period in winter. There is now a yellow form available besides the more usual orange. The yellow one will now come back true from seed which it did not do until a few years ago. If you cross the yellow with the orange, however, the orange will dominate and you could lose the yellow altogether.

Jatropha podagrica orange

Jatropha podagrica orange

Jatropha podagrica yellow

Jatropha podagrica yellow

This plant is found in Africa and can take a lot of drought. It is an ideal plant for the living room; it can be grown in the full sun, so a windowsill is no problem and it can take the dry heat of the central heating. It is very easy to grow from seed, but the seed needs to be fresh. It can germinate within one or two days. The more sun it gets, the quicker it will flower, possibly within six months.
Wild Adeniums are usually various shade of red, but occasionally white ones do appear. In Thailand, a lot of breeding has taken place and because of the inherent colour variation in the wild plants, a whole range of colours are now available in cultivation, ranging from white to very dark red and all shades in between. Efforts are now made to produce a true yellow one.

Adenium obesum pink


Adenium obesum alba

Have a look at the post on Pachypodium bispinosum for more information on the germination of the seed.

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