Dregeas come from Asia and are evergreen in the wild, but if you keep them in your greenhouse with low winter temperatures, they will lose most of their leaves. They are also known under their synonym Wattakaka sinensis.
It is a climbing plant that will flower every spring with white flowers that have a splash of pink in the centre. They are highly scented, which usually means in these type of plants that they are moth-pollinated. The flowers last for up to a week and resemble hoya flowers. Not surprising as Hoyas and Dregeas are related. Another asclepiad species that has highly scented moth-pollinated flowers is Araujia sericifera, although the flowers on that plants do not resemble Dregea flowers.

Dregea sinensis

Dregea sinensis

As with Hoyas, Dregeas rarely set seed in the greenhouse, but when they do, they form twin-seed horns which will burst open when ripe and can contain up to 50 seeds. The seeds remain viable for up to a year, but it is better to sow them as soon as possible. If you sow them straight away, you will get almost 100% success; if you leave it till 3-6 months, you will get 25-50%; and after a year, you may only get one or two to germinate.
The leaves are heart-shaped and fairly large. It is possible to propagate this plant by cuttings, preferably in the spring. I use cuttings with two nodes, one for the roots and one for the new growth, just as you would do with Hoyas. They can be grown in shade or full sun and will grow outside in the summer. They can have a bit of frost (-2 or 3°C), but it is better to give them some protection.

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Before 1994, few Hoya species from Sulawesi were in collections, but in that year a group of Hoya enthousiasts spent three weeks collecting Hoya material on the island. About seventy numbers were collected, but as they were not in flower, some species were collected several times. The plants were brought back to Holland, grown on and brought into flower. One of the species collected was at the time given the number 114, later changed to 8864, and only determined as Hoya pallilimba by Ruurd van Donkelaar and David Kleijn in 2001 (‘Taxonomy and ecology of the Genus Hoya’ in Blumea, 46/3, pp. 457-483). The pallilimba was found by the Ranu River in the Morowali reserve and is a species that grows in association with ants. The ants (genus Tetramorium) take the seed into holes in branches to store as a food supply; the seeds that are not eaten will germinate and grow from the hole. The plant is not solely dependent on the ants; seeds that drop into leaf litter in the fork of branches will also germinate.
Pallilimba is a hanging species that is not very free-flowering. It also has to be reasonably large before it will flower. The plant itself when not in flower is very similar to two other species on the island, Hoya brevialata and Hoya myrmecopa. It is a lot easier to tell them apart, when the plants are in flower. Brevialata has much larger flowers and can be red or white. Myrmecopa has flowers that hang down as buds but which will stand upright when open. Pallilimba flowers are smaller and always reddish in colour.
The plant is reasonably easy in cultivation and can reach a length of 1.50 mtr. It is best grown in a hanging pot to give the stems enough room. It is easily propagated from cuttings; in the summer they will root in about 10-12 weeks. The plant requires higher temperatures than many of the other hoyas, around 20°C minimum.

Hoya pallilimba GPS8864

Hoya pallilimba GPS8864

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

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

Biophytum sensitivum comes from Africa and India and grows to about 20cm high in a rosette which gives the impression of a small palm tree. As with other similar plants, such as the Maranta, the leaves shut at night. It does not require special soil, but keep it moist at all times. Most people know the plant Mimosa pudica, the sensitive plant, but another plant, less well-known, is the Biophytum sensitivum which also has similar properties of being able to close up its leaves for protection. However, in this case, the leaves are folded downwards whereas on the Mimosa they are folded upwards. The only pests that may attack the plant are fungus gnats whose larvae gnaw away at the base of the stem. In the wild, other plant-eating insects will try to feed on this plant, but to combat this, the plant folds its leaves and the insect falls off. As the leaves also contain the poison oxalate, it is not clear why the plant has this additional leaf-folding protection.

The Biophytum was first described in 1753 as Oxalis sensitivum, possibly because Oxalis and Biophytum shoot out their seeds in similar ways. This is a sure way of reproducing itself as at least some of seeds fall onto good soil and will germinate quite quickly. Watch out for this phenomenon in your greenhouse, as you may end up with Biophytums all over the place. This only happens if you keep the temperatures above 16° C. at all times, as they do not like cold. It is an ideal plant for terrariums with their high humidity and low light, because that imitates their natural conditions. It is an annual, but it will live for more than one year. Make certain to save some seed while it is available, because the plant may suddenly die and you would be left with nothing. The flowers do not have to be cross-polinated, so one plant is enough to produce seed. When the seedpod is ripe, it will open up into a star-like structure in which you can clearly see the seeds. It opens up in the morning and by the afternoon, all the seeds have sprung, so make sure to collect them in time.

Biophytum sensitivum

Biophytum sensitivum


Biophytum sensitivum seed pod

Biophytum sensitivum seed pod

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