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


 

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This plant comes from Socotra which is an island belonging to the Republic of Yemen. It is one of a number of unusual caudiciform succulents that occur there. It can reach a height of 2 metres and looks very imposing. In the greenhouse, it should be kept warm and it will not lose all its leaves. You require two plants to produce seed. Normally, Dorstenias produce seed freely without having to be cross-pollinated, but Dorstenia gigas is one of the exceptions. Propagation by cuttings is very difficult, but there is a nursery in Holland that propagates this plant by means of tissue-culture.
They grow reasonably quickly in cultivation, especially if kept warm and given reasonable amounts of water. It will start to flower when it is about a metre tall which can take several years. It can be grown in a variety of soils, but do bear in mind that the colder the greenhouse, the more grit will have to be added to the compost to avoid rotting.

Dorstenia gigas

Dorstenia gigas leaves

Dorstenia gigas

Dorstenia gigas young plant

Ceropegia rupicola comes from Yemen; Ceropegia aristolochioides comes from an area between Senegal and East-Africa, in other words, from the tropical area just south of the Sahara. Normally these two species do not come into contact with each other, but in collections this is quite possible and this is what happened. The result is the cross of which you see the flower in the picture below.
The flower and stem are similar in structure to that of C. aristolochioides, but it is much larger. Barring the difference in size, the plant could easily be mistaken for an aristolochioides, but for the fact that the seeds were definitely collected from a rupicola plant. One of the reasons that there are not more hybrids from these two species, unlike for instance C. sandersonii and C. stapeliiformis which produce many hybrids, is because rupicola is difficult to keep in cultivation and you need to have a large plant before it flowers.
The C. rupicola x aristolochioides prefers conditions more like those in the natural habitat of C. aristolochioides, that is: hot and moist, rather than the dry heat in which C. rupicola grows. It can take drier conditions, but then it will not grow so very fast. In cultivation, it can also take cooler conditions, down to 15°C, but it does a lot better when it is kept warmer.

 

Ceropegia rupicola x aristolochioides