The Mystery of the Yellow Octopus....no, not a creature with 8 arms, but a lovely flower, the Gardenia. And here we have another guest blog from Andre Jagger with his deep dives into taxonomy and chemistry. Here this plant was first described exactly 200 years before I was born.
Over to you Andre:
A popular favourite in western gardens is the Gardenia, the heavy scent that hits the olfactory senses from those white to pale cream flowers found in great abundance wafts on the warm Spring air... For many the Gardenia, in question, originated from South to South-East Asia and is known as Gardenia jasminoides.
It was a British linen merchant and naturalist who first described the species in the Philosophical Transactions of the Royal Society of London and his text dated 20 November 1760 was published the following year. It is interesting to find plants for which both their genus and their species have not been revised in the last 250 years, this being one of them.
You may all be familiar with this plant in the modern day cultivars, double flowers, longer petals, smaller sized plant, smaller leaves, longer flowering period, and so on. The Chinese had already been busy selecting the crème de la crème of potential candidates for preservation over the last one thousand years. It is widely loved in China ... and so it should be too!
In Hong Kong, this plant is native to the foothills, slopes and gullies and is found in the single petalled form. It is native to Bangladesh, Cambodia, China North-Central, China South-Central, China Southeast, East Himalaya, Hainan, Japan, Laos, Taiwan, Thailand, and Vietnam. I have occasionally found it around the 250 metre mark, more often amongst the dense shrubs and understory of moderately forested low hills. In this case, I found one along the coastal area of Yam O Peninsula on the popular path to Luk Keng Tsuen. I can't recall there ever being a perfume with the flowers but I didn't on this occasion take a specimen for close examination. However, I recall back in 2014 along the Shek Lei Pui Reservoir I saw a very large shrub that had these unusual looking seed pods on it. The pods were octopus like and yellow! I did stop to examine them and took some photos quite late in the afternoon. Amazingly enough they proved useful and now adorn this picture and provide substantially more colour to it ... Having needed to do something with some happy snaps taken of the flowering plant in 2020 I put the lot together without realising how significant the plant was to Chinese Medicine.
It so happens that yellow colouration in the aged petals and the yellow colouration in the fruits are derived from similar chemicals, they are a glycosylated carotenoid, based on a alkene dicarboxylic acid, Crocetin. Whilst crocetin has a longish central hydrocarbon (alkene) chain that makes it insoluble in water, the acid functional groups at either end do little to improve this. So crocetin is a red pigment that is largely fat or oil soluble. It is found in the older yellow petals and perhaps more obviously the fruits of this species. However, the bulk of the yellow to orange colouration comes from the crocins, they are the glycosides of crocetin. The glycoside being a saccharide attached via a glycosidic bond (an ether / oxo bridge) to crocetin. This glycosidic alteration of crocetin achieves two ends. The first is to vary the color from the burnt or brick red to a more yellow state. The second, being to make the molecule more soluble in water. Saccharide diesters of crocetin vary from yellow to orange and if the saccharide is Gentiobiose, then the known crocin pigments; crocin1, crocin2, and crocin3, are obtained. If both carboxylic acid functional groups of crocetin undergo esterification via glycoslation with gentiobiose then the result is Crocin ( also known as Crocin1). The other crocins arise when either only one of the carboxylic acid groups is esterified with Gentiobiose or another saccharide or both are variably esterified by other saccharides. Quite a few possiblities could occur but not all have been noticed yet in plant tissues.
The combination of crocetin and crocin in the fruit of G. jasminoides give the colours that are seen, this varying with age and maturity of the fruit. Both crocin and crocetin are known to have a tremendous health value and there is plenty of literature on that subject. One reason for the long found use in Chinese Medicine. It is to be noted that the fruits have a slight odour and that they taste slightly acid but very bitter ... As is often said - they are a bitter pill to swallow ... Extracts of the fruit are readily available in China. It is of note that most saccharides would have been thought to taste sweet or be tasteless. However, Gentiobiose has a bitter taste, despite it being constructed from two glucose units. Currently, the use of these very beneficial crocins and crocetin is a deep area of modern medical and biochemical research.
On another note, the crocins are used as dyes and have been used with silk, in painting, also in food and food preparation.
As far as the octopus goes, the legs are just the residual calyx lobes that remain long after the corolla (petal tube) has detached. The head of the octopus is the ovary where the seeds develop.
Finally, if you wonder where the name crocetin and crocin come from then look no further than Crocus sativus, the source of that spice kown as saffron. The yellow-orange colour of saffron is primarily the result of crocin. This will not be my parting shot on Gardenia jasminoides, for there is much more to discover with the remainder of its rich and interesting biochemistry, particularly the iridoids.