Kusagi, the Stinky Tree

Clerodendrum trichotomum
More after the break.




I bought this plant for the exquisite jasmine-like scent of the flowers. Unfortunately, the Clerodendrum trichotomum I have is not as fragrant as other examples I have encountered. It is still a strikingly beautiful small tree.

Hardy and fast-growing, this is an ideal small tree for a medium-sized garden with poor soil. Mine is a very small garden with a rich soil so I am considering getting rid of it so I have more room for other fast-growing plant bullies. Too much plant food will make it produce more leaves than flowers. The tree can be cut back very low and springs back in less than a year.

Flowers in Manchester open from the last days of July up to a few survivors in late October. Though this year mine has produced a second set of buds coming in late October. The long heatwave obviously convinced it that it is living in one of the warmer countries of its native range. It produces deep blue berries in October and November. These are called drupes by botanists but I will be using the term "berry" in its colloquial, non-jargon sense. The young stems are covered with a thick velvety down, sometimes maroon and sometimes pale grey.

The leaves start late and fall at the start of winter after becoming tinged with maroon. Because of these large leaves the plant can be damaged by high winds. Even though it is against a wall my tree lost a branch that made up a third of its size in one heavy storm. It soon grew back, bigger than ever.

I have only found one seedling so far. If I wanted more plants I could get them very quickly by planting cuttings. I used some prunings with the leaves stripped off as plant supports and had to pull them out again when they rooted.

Parsonage Gardens tree in full flower in mid-August.

I am not sure if mine is a different variety from the one at Parsonage Gardens in Didsbury or whether the differences comes from mine being overfed. The Parsonage tree produces far more flowers with a stronger perfume and the leaves are not as lush as mine. It is obviously a lot older and has not been pruned back as much as mine.

The trunk of the Parsonage Gardens tree looking convincingly old.

Parsonage Gardens, close-up of the flowers.

It might be surprising to some that this plant is now in the same family as mint, the Lamiaceae. You would not expect a tree with fleshy berries in the same family as mint. That family is huge and contains many, varied plants. Not just the sages, lemon balm, basils, thymes, rosemary and other well-known kitchen herbs. Many plants which used to be in the Verbenaceae were recently added to the Lamiaceae. Teak, famous for its timber and growing to 40 metres (130 feet) tall, was also recently moved to the mint family.

I had thought that the names Glorybower and Glory Tree were given to the plant because of the Greek word for "fame" or "glory" κλέος, such as in Cleopatra - father's glory. However, I was surprised to discover that the OED has the origin of Clerodendrum as Greek κλῆρος chance + δένδρον tree. Liddell & Scott's "A Greek-English Lexicon" has κλῆρος as "lot", the drawing or casting of lots or allotments (in the sense of land or goods assigned by the result of a lottery, rather than a rectangular council-owned garden).

The first three species of Clerodendrum that were described by botanists were Clerodendrum infortunatum (unlucky Clerodendrum in 1753), Clerodendrum fortunatum (lucky Clerodendrum in 1763) and Clerodendrum calamitosum (disastrous clerodendrum in 1767). Presumably this is why they were associated with chance or lotteries, being called Lotboom (lot tree) in Dutch and Loosbaum or Losbaum in German.

The naming of the first two species as the lucky and unlucky Clerodendrums appears to originate in translations of the local names Pinna and Pinnakola respectively by Paul Hermann in his Musaeum Zeylanicum in 1717. However, it seems that Pinna පින්න and Gas Pinna ගස් පින්න, (meaning "Pinna tree") are accepted names for Clerodendrum infortunatum in Sinhala. Pinnakola appears to simply mean "Pinna leaf". The leaves are used to wrap finger millet cakes in modern Sri Lanka. Clerodendrum infortunatum is still a popular medicinal plant in Sri Lanka. The word පින්න (Pinna) also means "dew" in Sinhala.

Experts on Clerodendrum consider that the modern Clerodendrum infortunatum is only native to Sri Lanka and identifications of the plant from other parts of India, Vietnam and Malaysia are other, closely-related, species.

Though Hermann stated it was a Sri Lankan plant, Clerodendrum fortunatum is not native to Sri Lanka or even in India. The confusion caused by these early descriptions has never been resolved. Clerodendrum fortunatum as is accepted in modern botany is a popular medicinal plant in China and Vietnam. The entire association with luck or unluckiness and the name of the genus Clerodendrum appears to have been a misunderstanding.

Clerodendrum splendens flowering about March 1842 in a stove in Chelsea.
Picture from Paxton's magazine of botany, and register of flowering plants.  
Biodiversity Heritage Library. 

The name Glory Tree seems to have been invented for the tropical African Clerodendrum splendens, despite the plant being a climber rather than a shrub. In Latin splendens means brilliant, shining or gleaming. The first descriptions are from 1824 but it does not seem to have been introduced to Britain until the plant was collected in late 1838 in Sierra Leone. It was called a stove-house plant as it needed well-heated greenhouses to thrive. The horticultural press raved about it in 1842, writing that the abundant, deep scarlet flowers rivalled the finest of other hothouse flowers then available.

The description and painting in Edwards's Botanical Register in February 1842 are given the English name Scarlet Glory-tree.  One of the editors of Edwards's Botanical Register (John Lindley) had a particular bee in his bonnet about Englishing botanical names for the benefit of both those uneducated in classical languages and those classical pedants who found the mangled Latin and Greek of botanical names offended their scholarly sensibilities.

By August 1844 Clerodendrum splendens plants were available for the "low" price of 10 shillings and sixpence, equivalent to perhaps £60 nowadays. They were sold by the Kingston (-upon-Thames not Jamaica) Nursery of Thomas Jackson, just 3 years after the first plants were coaxed to flower in Britain. The imported novelties were a lucrative trade for Victorian plant nurseries.

The plant-sellers clearly recognised that Glory-tree was a good name for plants, even if those plants had been introduced 50 years before the climber after which they would be named.

I can't find a mention of "Glorybower" before 1918, when it was mentioned in the report of a US experimental station in Puerto Rico. That report is not available in full on the internet. In 1923 a US catalogue of standardised names for commerce has Harlequin Glorybower for Clerodendrum trichotomum.

English botanical jargon does have the word "trichotomous", meaning branching in threes. The specific name for the Harlequin Glorybower comes from the description "panicula trichotoma", the flower clump divides by threes. I will have difficulty forgetting my misunderstanding that it means haircut. Exactly the same word τριχοτομέω (trichotomeo) means both "haircut" and "trisection" in Ancient Greek.

Clerodendrum trichotomum was a native of China, Taiwan, Japan, India, Korea and SE Asia. In China the tree is known as 海州常山 Hăi Zhōu Chángshān. Hăizhōu is an area of China in modern Jiangsu. Chángshān is another popular Chinese medicinal herb, Dichroa febrifuga in the Hydrangea family (Hydrangeaceae).

Clerodendrum yunnanense (滇常山, Diān Chángshān, meaning Yunnan Chángshān) has been used to adulterate commercial Chángshān (Dichroa febrifuga) herb.

In Japanese the tree is called クサギ Kusagi, but also Koshun-kusagi, Koba-kusagi and some other kusagi. Engelbert Kaempfer gave a brief description in 1712, writing that Kusaggi means "stinking plant". Google wants to translate クサギ as "Rabbit", so I am not sure if it supposed to stink like a rabbit or if that is just an artefact of the automatic translation.

The leaves are only smelly when crushed. They smell of a sort of yeasty/Vitamin B supplement/woundwort. Not unbearable and not very strong but with an unwelcome staying power in the nose. Some people compare it to peanut butter but I don't get that from it at all. The 18th century botanist Karl Peter von Thunberg described it as stinky like Mandrake. "Odor foliorum virosus mandragorae". I can smell the similarity to the unpleasant odour of the leaves of Datura wrightii, which is another poisonous member of the potato family to which Mandrake also belongs. I have never been close enough to a live Mandrake to know what they smell like. I have not smelt a rabbit hutch for a long time.

According to a government report of 1889 the plant was used in the Japanese northern island of Hokkaido. The name of the plant in Hokkaido (Yezo) is given as To-ŭ-no-ki. The dried leaves were regarded as edible. The roots and leaves were used there against fever.   A wood-boring moth caterpillar found in the tree called kusagi-mushi (kusagi grub) or tō no ki mushi was frequently sold to apothecaries who pickled it in soya sauce. The large caterpillar was given to children as a medicine against convulsions and parasitic worms. The moth was reported as Hepialus aemulus but is now known as Endoclita excrescens and is known to eat the wood of a wide variety of Japanese trees and other plants. The adult moth flies quickly and is large enough to be mistaken for a small bat.

Close-up of fur.

Autumn stem showing maroon fur.

I separated the leaves from the branch above and left them to dry for a week. No heat was applied, just kept at room temperature, with the leaves well apart on a metal grille out of the light. The nasty smell had disappeared by the time the leaves were completely dry. They still had a mild, unobjectionable smell that seemed familiar but was not something I could place. The range of medicinal dose recommended in the Chinese Herbal Medicine Materia Medica of Bensky et al is 4.5-15g and the herb is regarded as very safe. I decided I should try it, though the herb is best collected just before the flowers open. I found one of the middle-sized leaves was 0.45g in weight. I crumbled it and made a tea by adding it to freshly-boiled water and leaving for 30 minutes. The resulting tea was pleasant, slightly astringent like a green tea. I did not notice any effects.

As a medicinal herb the dried leaf and small stems are widely used. First described in Chinese medicinal literature in 1061 AD. The herb is called 臭梧桐 Chòu Wútóng in China (in Japan shūgodō, Korea chwiodong). This means Stinky Wútóng. Wútóng being Firmiana simplex (in the West called the Chinese parasol tree), from the Cola and Mallow family, Malvaceae.

Clerodendrum trichotomum herb is also, though less often, called 八角梧桐 Bājiǎo Wútóng, Bājiǎo meaning Star Anise. It is substituted in some areas of China with Clerodendrum fragrans (which may have been the original plant used to make this medicine) and Clerodendrum bungei.

Dà Qīng Yè (大青叶, simply meaning "big green leaf") is now usually a species of woad (Isatis indigotica, in the cabbage family) in the north of China or another indigo-producing plant (Baphicacanthus cusia, in the acanthus family) used in the South. However, the medicinal herb is thought to have been Clerodendrum cyrtophyllum originally. Clerodendrum cyrtophyllum still goes by the name Dà Qīng but is now only used medicinally in parts of Jiangxi province.

In Bangladesh the Clerodendrum trichotomum is called Chapa-genda. Leaf, stem and flower used against rheumatoid arthritis, skin diseases of the heart and skin.

The berries are denim-blue, though reversing the usual state of affairs by starting faded and getting deeper blue as the berry matures. The dramatic contrast between the red calyx and the blue berry helps draw the attention of fruit-eating birds which spread the seeds to new locations. The small size of the berry is to enable even quite small birds to swallow the berry whole, without damaging the seed. The red star-shaped calyx starts out folded around the ripening berry to protect it. When the berry is fully ripe the calyx unfolds into a flat star behind the berry.

The contrast between the calyx and the berry is probably much more dramatic for birds. Birds have light-detecting pigments in their eyes tuned to 4 wavelengths; ultraviolet (UV), blue, green and red. Using a piece of white A4 paper as a UV detector I determined that the red calyx reflects UV light at both 365 and 375nm wavelengths (UV torch and UV keyring, respectively). The dark blue berry glowed bright blue under both types of UV. I assume this is simple fluorescence that would result in absorption of the UV. The UV light is absorbed by the molecule and then given out again in a different color. Thus, under daylight the berry would appear to a bird to be intensely blue but have no UV, red or green reflection. The calyx would contrast sharply with high UV and red but no green and only a little blue reflection. The leaves are UV and green reflective but absorb red and blue.

Kusagi berries glowing, illuminated by a 365nm UV torch at night.

The striking blue colour of the fruits is due to an unusual indole pigment called trichotomine (and at least eight sugary derivatives like trichotomine G1). This compound has a centre very like the indigotin that is found in woad and indigo. Indigo is used to give denim its characteristic blue (or is the colour indigo?). Kusagi berries have been used in Japan to dye textiles and to produce natural inks. The technique of using kusagi as a dye has its own name, kusagi-zome with a recipe at the link.

The heart-shaped fruit contain two seeds. The more spherical fruit only contain one.

The colour intensity of trichotomine is over three times greater than indigotin due to the molecule being twice as heavy and the molecule having a greater surface area to catch light. Trichotomine has a colour intensity over half that of the leading synthetic food dye Brilliant Blue FCF.

Trichotomine is also hugely more soluble in water than indigotin. 24g will dissolve in one litre of water at pH 3 compared to only 0.00055g/l for indigotin. This is probably not a useful feature for a dye as it would wash out more easily. Unless the water-loving parts of the molecule are the bits that attach to the textile.

Development of trichotomine or its sugar derivatives as a food colouring is hampered by limited supply of the small berries and small amounts in each berry. Before it can be released commercially, lots of research would have to done on the safety and stability of the pigment in food as well as production techniques. The food additives company San-Ei Gen F.F.I. Inc. (with their headquarters in Osaka, Japan) have investigated the pigments in depth but have not yet managed to bring a product to market.

Of course, we all know that the pigment found in red cabbage changes colour with pH. When acid it is bright red, when alkaline it is blue and when neutral-ish it is purple. This limits the use of red cabbage pigments to red or purple colouring in most foods, as most foods are acidic or neutral. In the case of trichotomine the blue changes to emerald green when made alkaline with a few drops of potassium hydroxide solution. Very, very strong solutions of potassium hydroxide will turn it yellow.

Six berries gently crushed in a little tap water and the seeds removed undamaged.
More intensely blue in real life.

The same mixture with a few drops of potassium hydroxide solution added.

Like most other members of the Clerodendrum genus this plant contains a wide range of unusual chemicals in different parts, even giving their name to a whole class of diterpenes - the clerodanes and neoclerodanes. Many species of Clerodendrum are used for medicine all over Africa and Asia. Some have been shown to be anti-inflammatory and to have other biological effects suggesting the medicinal uses may have some foundation. Of course, we have little dependable information on long-term benefits and drawbacks to their use compared to more well-studied medicines.