Trachelospermum jasminoides or star jasmine is the most gorgeous climbing shrub, furnishing walls with beautiful evergreen foliage all year and then filling the garden with wonderful perfume for a full two months in the summer.
Once again I realise that I have taken this plant for granted, not giving it the attention it deserves. So, this year, I have savoured its glorious scent even enjoying it inside as it wafted in through the open door. I have looked more closely at the flowers, noticing for the first time the unusually-shaped buds and the way the petals fold back on themselves when they open.
I have noticed what a neat plant it is, covering its allocated space from top to bottom with a minimum of attention, and not protruding too far from the wall.
And then lots of other questions occurred to me. Where does it come from? To which family does it belong? And are there other similar plants that might be good to grow?
Hopefully, I have gone some way to finding the answers.
Let’s start at the bottom and work up
Trachelospermum jasminoides is often described as a climber or vine but is, more correctly, a liana. A liana is woody vine that has roots in the soil and uses trees and other structures as support as it grows up towards the light. They are a characteristic feature in tropical forests but can also be found in temperate regions. Lianas often have stiff young stems compared to the soft, flexible new growth of other plants and I have found this to be the case with trachelospermum,
I planted mine against a wall about fifteen years ago. I restrict its height to about 3.5m and, with one pruning each year, it only protrudes about 50cm. A quick glimpse behind the scenes reveals how this has come about. The original main stem immediately divided into three and these are now gnarled and woody and about 5cm across. As they grew they divided again and again and became thinner as they rose and are all now very woody. But what is very noticeable is that they all hug the wall. I put wires up for support and perhaps they were necessary when the plant was young but now it seems that the whole structure is self-supporting. I also notice that new shoots at the back of the plant, when they touch the wall, grow straight up as though attached to it by some magnetic force. Stems at the front do not have this same inclination.
Shoots grow out forward from this structure and, although they are also quite woody, they carry the leaves and flowers.
The leaves fall forward and are arranged to catch the light. Similarly, the flower heads fall down but each flower faces straight outwards. I hope you can see this arrangement in the photographs.
The simple leaves are dark glossy green, opposite, ovate-lanceolate, about 30mm by 80mm, with 8mm petioles. The inflorescence is a cyme with quite a long peduncle, which grows from a leaf axil.
The stems and leaves exude a sticky white latex when cut and the whole plant is poisonous.
Now we can take a close look at the remarkable flowers
Each flower has five sepals, united only at the base of the calyx and with reflexed tips. The five petals are fused into a tube for half of their length and then open out into a star shape reminiscent of a child’s windmill, and about 25mm in diameter.When seen from the back we can see that it is the folding back of the petals that produces this unusual shape. Each flower does not last long and, as you can see in the images, they are easily bruised, but as each one fades another bud opens and this succession provides its long flowering season.
The pistil and stamens are held within the corolla tube and do not extend beyond it. I had, therefore, to dissect the tube to see them. Although not completely successful, I think you can see the style with a pointed stigma and the stamens, which are attached to the corolla tube about half way up. The stamens bend inwards forming a cone over the stigma and there are pollen grains visible.
There are also hairy ridges within the tube, presumably where the petals join, and, if I zoom in on the centre of the flower, you can see the five ridges and the tip of the stigma surrounded by the tips of the five stamens.
Where are the seeds?
As I was gathering this information I realized that I have never seen any fruits or seeds on this plant. As you can see in the image, the flowers have dropped, leaving the stem with the calyx and style. Not long afterwards they too fall to the ground. Of course, this is not unusual for garden plants for a number of reasons but my curiosity was aroused so I tried to find out what pollinates Trachelospermum jasminoides and what effect the arrangement of the sexual organs has on that pollination.
I saw several references to the perfumed flowers attracting bees. I have many plants that are covered in insects, including bees, but I don’t think I have ever seen them on the trachelospermum. I found some references, in a scientific paper and an online forum, to hawk moths being pollinators.
Bearing in mind the enclosed nature of the flower, this would seem more likely, as most hawk moths have a long proboscis with which to feed on nectar. But, in the absence of any definitive information, these questions remains unanswered.
However, Trachelospermum jasminoides certainly does produce seeds. These seed pods, more correctly termed follicles, were about 11cm long and the seeds 12mm, without the coma, extraordinarily long considering the size of the flower. This photograph was taken and shared online by someone in the Netherlands.
If you have any experience or information do, please, post a comment.
Where does Trachelospermum jasminoides grow in the wild?
Trachelospermum jasminoides is native to central and southern China, Tibet, Vietnam, Korea, and Japan. As we have already seen, it is an evergreen liana and, in the wild, can grow to over 7m. Roy Lancaster, in his book, Travels in China – A Plantsman’s Paradise, describes the unforgettable sight of it climbing the stems of trees in the hills above the West Lake in Hangzhou, Zhejiang province. Plastered with sweet-scented flowers it appeared as a solid column of green up to 9m or more. It was introduced into cultivation from Shanghai in 1844 by Robert Fortune.
How to grow Trachelospermum jasminoides
When Trchelospermum jasminoides was first introduced, it was thought necessary to grow it in a greenhouse. It is now considered to be hardy throughout most of the UK although it does appreciate a sheltered spot, especially in colder areas. It needs a well-drained soil in sun or partial shade and a support on which to grow. I have also seen photographs of it grown as a hedge or allowed to scramble over other plants or bare soil but have no idea how successful these last two methods might be!
Some relatives that might surprise you
Trchelospermum jasminoides is in the Apocynaceae family, a name derived from the Greek apo, asunder, and kyon, a dog. The type genus, Apocynum, dogbane, was supposedly poisonous to dogs, hence the common name of dogbane family, although it is also called milkweed family because of the white latex that exudes from damaged leaves and stems.
The family contains 376 accepted genera with over 5,000 species of trees, shrubs, herbs, succulents, and lianas. The leaves are simple, opposite or whorled, and evergreen or deciduous. The flowers have five sepals, partially fused, and five petals, fused into a tube with distinct lobes, commonly resembling a windmill, although they can be star or bell-shaped. The five stamens are partially fused to the corolla tube.
Plants in the Apocynaceae are native to the European, Asian, African, Australian, and American tropics or subtropics, with some temperate members. Trachelospermum is a genus in this family and, although there are ten accepted species, it is T. jasminoides that is the most popular and widely grown in the UK.
When I first looked through the very long list of genera, I didn’t recognize many of the names. Most of them I had never heard of before but there were a few names that rang a bell.
The first to catch my eye was Asclepias. This used to be in the family Asclepiadaceae, the milkweed family, which is now classified as the subfamily Asclepiadoideae of the dogbane family, Apocynaceae. But why was this name familiar?
Just a little research jogged my memory – monarch butterflies. Monarch butterflies embark on an amazing migration from NE United States and SE Canada to the mountain forests in central Mexico a distance of some 1,200 to 2,800 miles. Here they find the right climate conditions to hibernate from the beginning of November to mid-March. They then begin their northern migration, during which female butterflies lay their eggs. Milkweed, Asclepias, is the only plant on which monarchs will lay their eggs and the source of food for baby caterpillars. This phenomenon is, of course, a lot more complicated than this outline suggests but does rely on milkweed of various species. There’s a link below if you’d like to know more.
Members of the genus produce some of the most complex flowers in the plant kingdom with a very complicated pollination mechanism. There’s a link below if you’d like to find out more.
In the UK we grow a few species and some cultivars and I saw quite a spectacular one at Sissinghurst Castle Garden. There was no label but I think it is Asclepias curassavica, tropical milkweed or blood flower. It is a very long-flowering tender perennial, usually grown as an annual, but it can be cut back and overwintered indoors. The native range of this species is Mexico to Tropical America.
Close by at Sissinghurst was another family member, Gomphocarpus physocarpus.
Gomphocarpus has a native range in Tropical and S Africa to Arabian Peninsula and the species Gomphocarpus physocarpus is native to S Mozambique to S Africa. It is a shrubby perennial that can grow to about 2m However, the one I saw was less than 1m and I imagine that in the UK it is grown as an annual. This plant, too, has complex flowers and complicated pollination mechanism which produces these inflatted ball-like fruits. It has many common names including the well-chosen hairy balls. Although in the photograph the fruits look as though they might be juicy, they are, in fact, inflated balls full of silky seeds like the ones we’ve seen in Trachelospermum and Asclepias.
This name was also familiar because I do grow one species, Dregea sinensis. It is a liana with pale green, somewhat tomentose leaves and long-stalked umbels of red-blotched, hoya-like flowers, which have a glorious perfume. It was introduced from China in 1907 by Ernest Wilson. Although moderately hardy in the UK, I grow mine in a sheltered spot and it has set seed, from which I’ve grown several seedlings.
However, beautiful though this plant is, it has an identity crisis. When I first came across it it was called Wattakaka sinensis. Who wouldn’t want to grow a plant called wattakaka? It then lost that name and was given a new one, Dregea sinensis. Not quite so catchy or memorable, I think you’ll agree. Plants in the genus Dregea have now been included in Stephanotis but D. sinensis is not one of them.
It is still called Dregea sinensis but, according to Plants of the World Online “This name is unplaced. Unplaced names are names that cannot be accepted, nor can they be put into synonymy.” It will be fascinating to see where it ends up.
Coming closer to home is the genus Nerium and its one species, Nerium oleander, a native of the Mediterranean region to SW Asia. This evergreen shrub with its white, yellow or pink flowers is a well-known sight to anyone who has travelled to the Mediterranean region but is only hardy in coastal or mild parts of the UK. In the wild it often grows in dry river beds, where it can cope with the extreme dry and with a sudden flood of water if it rains. The image shows nerium growing in a wadi, a dry river bed, in Libya.
It has been in cultivation for a very long time. Nerium is the classical Greek name and it was very popular in Roman gardens and was often depicted on murals in Pompeii. John Gerard mentions growing it in his London garden in his Herbal of 1597 and it remains popular
today as a plant for the conservatory or a hot, sunny spot in the garden in summer.
Last but not least is Vinca. I must admit I was surprised when I saw this genus in the list of members of the family Apocynaceae, that such a humble plant would be at home in such exotic company. Some regard Vinca as a British native, especially the species V. minor, whereas others believe it be a naturalized introduction, possibly brought here by the Romans. Even if it was an introduction from Europe it has been here a very long time. It is mentioned in fourteenth century writing and John Gerard, in his Herbal of 1597, wrote, “They grow in most of our London gardens.”
Vinca species are vigorous, evergreen, trailing shrubs making extensive ground cover but often seen at their best scrambling up a boundary hedge.
When I started this post all I knew was that I had a very attractive, easy shrub with beautiful, perfumed flowers. Visitors who came when it was flowering always commented on it, especially the perfume, so I thought it would be a good candidate for a bit more research..
The first surprise was that I had never heard of the family Apocynaceae and, from there, each new piece of information I found opened up yet another avenue to explore. I was enthralled by the intricate flowers but still need to do more work on the fine detail and to find out why they don’t set seed. Reading about explorers and plant hunters is always interesting as is trying to imagine how plants grow in the wild. I went to China to enjoy reading about some of Roy Lancasters expeditions and then on around the world to find out about some of the family members. I had a glimpse of the huge subject of the monarch butterfly and the effect that human activity is having on its life cycle and, in contrast, how artists over the centuries have depicted nerium in beautiful paintings.
It has been a fascinating trip and I hope you have enjoyed reading about some of what I found on the way. There are lots of links below if you fancy finding out more.
Find more information
- Plants of the World Online
- Flora of China – Trachelospermum jasminoides
- Asclepias pollination
- Wikipedia article on monarch butterfly migration
- Wikipedia article on Nerium
- Asclepias curassavica seed from Special Plants Nursery
- Travels in China A Plantsman’s Paradise by Roy Lancaster
- The Hillier Manual of Trees and Shrubs
- The Plant Hunters by Toby Musgrave, Chris Gardner, and Will Musgrave
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