Choisya – Mexican orange blossom
Choisya is a genus of shrubs, some of which have become very popular in the UK because of their ease of culture, their evergreen foliage, and their attractive, perfumed, white flowers in the spring. When a plant is as popular as choisya, it tends to become ubiquitous and then dismissed as too ordinary.
But I wanted to know more – why that name, where’s it from, what do those little flowers look like, and where does the perfume come from?
Here’s what I found.
Where is it from and why the name?
The genus Choisya contains six species native to southwestern United States and Mexico. It was introduced by Alexander von Humboldt and Aimé Bonpland with the name Choisya dedicated to Swiss botanist Jacques Denys (Denis) Choisy.
Alexander von Humboldt was an adventurer, explorer, and scientist who, together with French explorer and botanist, Aimé Bonpland, undertook a scientific expedition of South America from 1799 to 1804. They returned to Europe with, amongst many other things, 60,000 plant specimens. Of the 6,000 species collected, 2,000 were new to European botanists. It took many years to publish all the information gathered and at some point German botanist, Carl Sigismund Kunth, took over the botanical publications and, between 1815 and 1825, published the seven volumes of Nova genera et species plantarum quas in peregrinatione ad plagam aequinoctialem orbis novi collegerunt /descripserunt, partim adumbraverunt Amat. Bonpland et Alex. de Humboldt.
In Volume 6, published in 1823, we find the genus described, together with the dedication, followed by a description of the type species, Choisya ternata, and an amazing botanical illustration. You can find it at the Biodiversity Heritage Library.
(Do take a look: it’s absolutely fascinating. You’ll need to scroll down a bit but you’ll soon get to Choisya.)
What does a choisya look like?
Choisya species are shrubs, which can grow to a height of between 1 and 3 metres. The leaves are evergreen, opposite, palmate with from 3 to 13 leaflets, leathery, and pitted with numerous, tiny oil glands. The pleasure derived from the aroma they exude when crushed seems to be a matter of opinion. Descriptions vary from the obvious, aromatic, to, like furniture polish, or plain, unpleasant.
The star-shaped flowers are bisexual, white, and arranged in cymes. Each flower usually has 5 sepals, 5 petals, and 10 stamens in two whorls. The superior ovary has 5 carpels. Here, usually is the operative word because, as you can see in some of the images, the number can be 6 for sepals, petals, and carpels, and 12 for stamens, although I have seen more than 12 stamens in some flowers. Again, the perfume of the flowers seems to divide opinion. I find it pleasant on the air but not so good at close quarters.
Which plants is choisya related to?
Amongst others, oranges and lemons! Choisya is in the Rutaceae, the rue family, sometimes referred to as the citrus family. They share the same basic flower structure but, obviously, the fruits are very different. They also have similar aromatic foliage and scented flowers. Choisya’s common name of Mexican orange blossom reflects the similarity of the flowers with those of the orange. They might look alike but I don’t think the perfume is anywhere near as delicious as the orange.
There are 152 genera in the Rutaceae but, apart from Choisya, Citrus, and Ruta, there were only three, Correa, Dictamnus, and Skimmia, that were familiar to me as garden plants here in the UK.
Let’s get specific
Choisya ternata was the species that Humboldt and Bonpland named and described. It is native to Mexico as far south as Central Mexico. It has become one of the most popular shrubs for British gardens and can reach about 3 metres high and wide. Being evergreen it has a presence all year but is spectacular when covered with flowers in the spring, often flowering again in the autumn. The white star-shaped flowers are about 3cm across. In this species, the dark green leaves have three leaflets, hence ‘ternata’, each one about 6-7cm long and 2-3cm wide. It is said to be hardy down to -10˚C and has received the Royal Horticultural Society’s Award of Garden Merit.
Choisya arizonica is a much smaller shrub, growing to about 1m. It is native to the mountains of Arizona, a fact reflected in its reduced hardiness, -5˚C. The leaves in this species are dark green with between 5 and 10 narrow leaflets, edged with wart-like teeth.
None of the other choisya species, listed below for completeness, are available in UK. From Plants of the World Online I have the names of the accepted species and their native ranges but and I haven’t found any descriptions.
Choisya dumosa has two varieties, C. d. var dumosa, native to Mexico Northeast, New Mexico, and Texas, and C. d. var mollis, native to Arizona and Mexico Northwest.
Choisya katherinae and Choisya palmeri are both native to Mexico Northeast.
Choisya neglecta native to a very small area, Mexico Central.
Let’s mix it up a bit – some beautiful hybrids and forms
Choisya × dewitteana ‘Aztec Pearl’ was the first hybrid produced. It was bred by Peter Moore, at Hillier’s nurseries in 1982 by crossing C. ternata with C. arizonica. This beautiful shrub grows to 1.5 to 2 metres high and inherits slender foliage from C. arizonica and increased hardiness and repeat flowering from C. ternata. The flowers are about 2.5 cm across and have pink sepals, which are visible between the white petals giving the plant a much warmer colouring than C. ternata. It has received the Royal Horticultural Society’s Award of Garden Merit.
Choisya × dewitteana WHITE DAZZLER is another hybrid bred by Peter Moore. It is compact, reaching 1 -2 metres in height and spread, and suitable for growing in a large pot. It has the usual white flowers and narrow-leaved palmate foliage. It too has received the Royal Horticultural Societies Award of Garden Merit.
Choisya × dewitteana ‘Aztec Gold’ is a cross between ‘Aztec Pearl’ and SUNDANCE developed by Alan Postill, plant breeder and propagator at Hillier Nurseries. It will reach 1-1.5 metres high, has the usual clusters of white flowers, and leaves, with three to five slender leaflets, that open yellow and mature to green.
Choisya × dewitteana SNOW FLURRIES I couldn’t find who developed this one but it is another with slender foliage and white flowers to about 1.5 metres in height.
Choisya × dewitteana APPLE BLOSSOM was bred by Peter Moore and is the first hybrid with pink and white flowers. Pink buds open into white flowers.
Choisya × dewitteana ROYAL LACE is similar to ‘Aztec Gold’ but is neater and more compact, only reaching 75cm high making it ideal for growing in a pot. It has slender golden foliage and white flowers.
Choisya × dewitteana GOLDFINGERS is a Peter Moore hybrid, a cross between C. ternata SUNDANCE and C. arizonica made in the early 1990s. He described it as a golden form of ‘Aztec Pearl’. It is compact at 1 to 1.5 metres in height with a 1 metre spread and suitable for pot culture.
Choisya ternata SUNDANCE is a yellow-leaved form of this common species. It started life in 1978 when British nurseryman Peter Catt noticed a tiny leaf with a white edge on an old Choisya ternata, from which he was taking cuttings. He took a cutting with the leaf, rooted it and forced it to grow from the leaf by judicious shoot removal. He envisaged a variegated plant so was amazed when a golden shoot emerged. The resultant plant, SUNDANCE, was launched at the Chelsea Flower Show in 1986. It has received the Royal Horticultural Societies Award of Garden Merit.
Choisya ternata MOONSHINE was found as a sporting shoot of C. ternata in 1992 by David Tristram and Tim Crowther at Walberton Nursery. It is similar to the species but its leaves are wider and flowers noticeably larger.
Take a much closer look
This first set of images are Choisya x dewitteana ‘Aztec Pearl. In the close-up of the bud you can see the dark pink sepals, which get paler as the flower matures. I have removed some of the petals to reveal the stamens, arranged in two whorls. In the outer whorl the filaments are longer than those in the inner whorl.
This is more obvious in the image of the open flower, where you can see the five petals and ten stamens. The anthers of the stamens in the outer whorl have opened to release their pollen, whereas those of the inner whorl are only just starting to split. This arrangement must extend the time when ripe pollen is produced, which would be of great advantage to the plant.
I then removed two of the petals and five stamens to uncover the style, stigma, and superior ovary.
In the image of the backs of the flowers you can see the bracts at the base of each pedicel, the bracteoles further up the pedicel, and the five sepals.
This second set of images are Choisya ternata. In the image of the inflorescence there are some flowers with five petals and ten stamens and some with six ptals and twelve stamens. It would seem to be a random feature.
The image of the back of the flower shows that the sepals and bracts are very much paler than those in C. x d. ‘Aztec Pearl’.
I selected a flower with six petals to look at in close-up and you can see the same arrangement of long and short filaments and the same stages of dehiscence as in C. x d. ‘Aztec Pearl’.
Again, I removed some of the petals and sepals to look more closely at the style, stigma, and ovary. Plants in the Rutaceae usually have nectaries in an annular disk at the base of the ovary and I assume this is what can been seen as a paler green band at the very bottom.
I then took a cross section across the widest part of the ovary to identify the six carpels, which are joined at this location, each with a locule.
Finally, I took a close-up image of a leaf of Choisya ternata against the light. Plants in Rutaceae usually have leaves with secretory glands containing ethereal oil, which appear as translucent spots. This is what you can see in this image.
Now, all we have to do is find out how to grow a choisya when we have one.
How to grow Choisya
Graham Stuart Thomas gives Choisya ternata a star approval in his book, Ornamental Shrubs Climbers and Bamboos, because he considers it a really good garden plant. He suggests that it is “specially suited to towns; in open country and exposed gardens it is apt to be damaged in winter, or during cold weather in spring.”
The RHS recommends growing in a well-drained soil in a sheltered position in full sun and that it is hardy throughout the UK down to -10˚C, except for Choisya × dewitteana ROYAL LACE, which is not quite so hardy.
In his book, The Well-Chosen Garden, Christopher Lloyd writes that he grows Choisya ternata in the shade of a Magnolia denudata. He says that it needs sun in the north to make it flower but, in the south, the ambient temperature is high enough to ripen the wood and enable it to flower even in the shade. He adds that the leaf colour will also be better in shady conditions.
Taking this into account together with what I’ve read and found on various sites online, it would seem that good drainage and shelter, especially from cold winds, are the most important things to consider. A sunny position or one in partial shade both seem acceptable and, as long as your garden isn’t very cold or susceptible to icy winds, it might be worth a try if you can find a sheltered niche. It would be interesting to hear how far north this is as popular a plant as it is here in the south.
Find more information
- Here’s another link to the 1823 document with a description of Choisya, at the Biodiversity Heritage Library
- Plants of the World Online – Choisya
- The Invention of Nature – The Adventures of Alexander von Humboldt the Lost Hero of Science by Andrea Wulf. Humboldt has more things named after him than anyone else – towns, rivers, mountain ranges, an ocean current, a penguin, a giant squid, and even a region of the moon. And yet we know so little about him. I’m looking forward to reading this book to find out more.
I have previously enjoyed two of Andrea Wulf’s books, The Brother Gardeners – Botany, Empire and the Birth of an Obsession and Founding Gardeners – The Revolutionary Generation, Nature, and the Shaping of the American Nation.
Isn’t it amazing where an interest in plants takes you?
- Ornamental Shrubs Climbers and Bamboos by Graham Stuart Thomas
- The Well-Chosen Garden by Christopher Lloyd
- RHS Encyclopedia
- The Botanical Garden by Roger Phillips and Martyn Rix
- Shrubs by Roger Phillips and Martyn Rix
- Garden Shrubs and their histories by Alice M. Coats
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