(A talk given at the LOG seminar in November 1999)
Ernest Hetherington aptly commented in 1994:
“A bit of advice often given to people, who are hurrying frantically through life, is that they should pause their mad dash for a moment of enjoyment. ‘Take time to smell the roses’, is appropriate for all of us who raise and enjoy orchids. As we enjoy the beauty of a flower, take time to know and appreciate its fragrance. Nowhere in the floral world is there a family of plants that produces fragrances to compare with those of species of the orchid family.”
|Miltoniopsis Jean Sabourin ‘Vulcain’
The colourful, long lasting flowers of the Miltoniopsis make them an ideal pot plant.
An added bonus is the soft, delicate fragrance that they emit.
In this discussion I would like to touch on the following aspects of fragrance:
Composition of fragrance
Moth pollinated orchids
Fly pollinated orchids
Bee pollinated orchids
Flowers pollinated by butterflies and birds
Transmitting of fragrance in hybridising
A few more examples:
Orchid fragrance is a relatively volatile substance found in plants. It is stored as essential oils in special cells (osmopheres) at the periphery of flowers, leaves or roots. Only small amounts are present as the substance can be toxic to the plant.
These fragrant oils can consist of few to many compounds. Being volatile, meaning that it readily changes into vapour at ordinary temperature, allows us to smell them.
As early as 1884 Darwin mentions osmopheric tissue in plants.
A lot of research has been done to analyse the components of floral fragrance to try and establish a link between fragrance and the pollinators.
I am not going to go into the methods of collecting fragrance and separating the fragrant compounds – There is ample literature on these fascinating chemical processes.
In a study mentioned in the AOS bulletin (Nov 1986) eleven major compounds most frequently produced in orchid flowers are mentioned ? They have all been previously identified from other essential oils and are widely distributed throughout the Plant Kingdom. I mention the following:
COMPOUND SMELLS ( SIMILAR TO) ORCHID EXAMPLE
2. SCENT PRODUCTION
It has been estimated that as many as 75% of all orchids are ‘fragrant’. That is , they emit detectable chemical compounds – some extremely fragrant while in some instances they are extremely repulsive smells.
Only some of the odoriferous compounds released by a flower are detectable by the human sense of smell, since these are complex substances closely related to the body chemistry of the pollinator they are ‘supposed’ to attract.
Fragrances are produced in specialized glands (osmopheres) which can be located anywhere on a flower or bud, depending on function. These are glands of intense physiological activity and are a large drain on the plant’s energy. The chemical turnover may be so strong that in some cases it can even lead to the development of warmth.
When non-fragrant flowers become isolated geographically fragrance may evolve as a pollinator attractant. There is, for example, a fragrant form of Phalaenopsis amabilis from New Guinea, although all other known forms of the species from other locations are without scent.
All flower parts can produce odours, from sepals and petals to calluses and basal spurs. Osmopheres in orchids may be diffuse and function only in very general attraction, or they are confined to certain regions of the flower so that pollinators are attracted to these specific areas and remove or deposit pollinia in the process.
Scent glands are most often situated on the lip – e.g. Stanhopea
Herschelia and Catasetum.
Members of the Catasetinae and Gongorinae subtribes produce the most voluminous quantities of scent known amongst orchids.
The fragrance of Catasetum flowers is interrupted within a few hours of pollination to conserve energy by limiting osmopheric activity.
The lip of an orchid flower is often its most attractive part. It is adorned with decorative and sometimes stunning masses of calli. These calli and other flower parts may contain unicellular trichomes (hairs), papillae and scales that produce starch, proteins, oil drops, fragrances and other substances to attract the pollinators. While feeding or scratching and gnawing the calli, the pollinators may pollinate the plant.
The intricate flowers of the scented Gongoras last only for two or three days but compensate for this by several opening in succession. It is found that if the lip (where the scent is produced) is removed, the flower lasts for two to three weeks.
In some cases other segments than the lip take over the function:
A urine-like smell is produced at the tips of the long tepals in Phragmipedium caudatum – Could this be to attract the ants who aid in pollination?.
The long tails of the sepals of Cirrhopetalum ornatissimum give rise to an odour of whale oil, while the lip smells of fresh herring!
Orchid floral fragrances are produced in a daily cycle with the time of maximum fragrance production generally being during the time when the pollinator of that species would be active.
Fragrance production consumes energy. Therefore the timing of scent production often coincides with the time of visitation of pollinators to use the least energy to achieve the maximum effect.
Lady of the Night orchid (Brassavola nodosa) will perfume a warm Summer’s evening with its heavy fragrance. The medicinal sweet odour is released shortly after sunset, reaching maximum strength around midnight, and fading quickly after sunrise.
In experiments done mainly with Brassavola, it was found that under conditions of extended artificially produced darkness, the flower scent remains, albeit at levels which appear lower than during the normal night cycle.
Results showed that scent release is strictly a light-controlled phenomenon and not regulated by some endogenous clock mechanism which is part of the orchid’s metabolism, but by a photochrome trigger.
Some more experiments concluded that it is actually the inflorescence which detects the presence or absence of daylight.
Fragrances may change throughout the day both quantitatively and qualitatively as well as from day to day:
Clowesia rosea smells of Vicks Vapo rub in the morning and cinnamon in the afternoon.
Catasetum expansum smells of turpentine in the morning and rye bread in the afternoon.
Bee-pollinated flowers are fragrant early in the day. Cattleya luteola, for example, is very fragrant between 4:00 and 8:00 am. It is usually visited by bees between 5:30 and 5:45. Most bee-pollinated orchids are not fragrant after nightfall and are barely scented at all on dark, gray days. Most of the diurnally pollinated flowers are brightly coloured.
Orchid fragrance may be produced at peak times during the day or night:
Some orchids such as Epidendrum difforme are moderately fragrant throughout the day with a peak fragrance production at night.
Others such as Epidendrum falcatum, change fragrance quality and intensity during the day, from the delicate, haunting scent of jasmine in the morning to a stronger note resembling that of Easter lilies or narcissi during the afternoon.
The Catasetum expansum smells of turpentine in the morning and rye bread in the afternoon.
Brassavola nodosa flowers produce a heavy fragrance and abundant nectar hidden deep in the cavity embedded in the ovary. The medicinal sweet odour is released shortly after sunset, reaching maximum strength around midnight, and fading quickly after sunrise.
Catasetum tenebrosum comes from Peru and adjacent regions of South America. The chocolate-brown, almost black flowers are spectacular, resembling birds in flight. They flowers emit a warm resinous fragrance with a sharp citrus note. Fragrance is apparent during the day, about four days after the flowers open and lasts until the flowers fade about three weeks later.
Encyclia radiata perfumes the greenhouse for an extraordinary length of time with a spicy floral fragrance. For a short time before the end of flowering the scent becomes slightly unpleasant. This then disappears and they become odourless for the last few weeks.
Encyclia fragrans smells of honey and vanilla in the mornings.
Encyclia lancifolia has a spicy fragrance.
FRAGRANT ORCHIDS AND POLLINATION:
Fragrant compounds can be manufactured synthetically and used to attract pollinators in the field. This helps to identify pollinators where field observations may be lacking.
In orchids, insects are by far the most important pollinators. Because of their small size insects have unusual visual characteristics inherent in their compound eyes. The repetitive visual field the insect eye produces will have great difficulty in seeing the colours of orchid flowers from any great distance, yet we all know that insects (bees, for example) unerringly head for flowers of specific colour. The initial attractant(over a long range) actually is fragrance in most of the instances. When the insect approaches a flower of ‘proper’ fragrance, it ultimately gets close enough to be guided visually to a successful landing.
Only some of the ordoriferous compounds released by a flower are detectable by the human sense of smell, since these are complex substances closely related to the body chemistry of the pollinator they are ‘supposed’ to attract.
MOTH POLLINATED ORCHIDS:
Nearly 8% of the orchid species are moth-pollinated (Phalenophilus), night-scented and they mostly belong to the African genera Angraecum and Aerangis. Delightful scents such as jasmine, honeysuckle, tuberose, lilies and gardenia are mostly given off at night. Flowers pollinated nocturnally (mainly moth?pollinated flowers) have strong nighttime odors and abundant nectar and are generally white or light green in colour .The light?coloured flowers also present a strong landing platform, a characteristically larger labellum, which is more readily visible to moths when they follow the scent trail to flowers. Good examples are most Angraecum and Brassavola species.
Both flower and pollinator are adapted to suit one another. Angraecum sesquipedale native to Madagascar is a well known example. This is one of the most beautiful and extraordinary Angraecum species. The large star-shaped waxy flowers are completely scentless during the day, but with the onset of darkness they exude an attractive and powerful scent until the following morning. The fresh-floral scent of the flower is fully developed by the third or fourth night. The pollinator (the moth Xanthopan morgani forma praedicta) needs a proboscis that matches the 20-35 cm long spur of the flower to reach the nectar at the bottom.
Flowers pollinated by moths of the family Sphingidae (sphinx or hawk moths) are called sphingophilous. They typically have a reduced labellum and long nectar tubes, e.g. Brassavola cucullata . The hawk moths are strong flyers and feed much like hummingbirds, hovering in front of the flower and extending their tongues deep into the nectary cavity.
|Both flower and pollinator are adapted to suit one another.
Angraecum sesquipedale of Madagascar is night-scented and [pollinated by a moth with a long probiscis matching the 25 – 30 cm long spur of the flower
FLY POLLINATED ORCHIDS:
In dramatic contrast to the night-scented orchids are the putrid and fecal scents of those orchids which mimic carrion in both scent (stench) and colour and thus attract carrion-feeding insects like flies. These are especially well represented by the Cirrhopetalum genus,which is spread across the whole of Southeast Asia.
Dracula chestertonii, an inhabitant of Colombia, mimics a fungus chemically and visually and so attracts the fly which normally lays its eggs on the fungus – this ensures pollination. The flower gives off a mushroom-like scent and the lip of the Dracula is similar in shape, size and smell to a fungus that live in the same conditions.
BEE POLLINATED ORCHIDS:
It is thought that about 60% of orchids are pollinated by insects belonging to the order Hymenoptera (bees, wasps…)
The flowers are fragrant with scents of lily-of-the-valley, rose, sweet pea, hyacinth, carnation, primula, lime-blossom, violet, narcissus and many combinations.
Scent is produced during daytime, the time the insects are active. Flower colour is often bright violet, blue , green and yellow.
Orchid-euglossine bee relationship:
Orchids like Coryanthes, Gongora, Stanhopea and Castasetum do not produce any nectar but attract their pollinators, male euglossine bees, by the intensity and quantity of their scent. Scent drops are collected on the hairy front legs of the bees and transferred to the back legs where it is stored. It is believed that the scent is collected and then converted to sexual pheromones which attract the females. In the process of visiting different flowers of the same species pollination takes place.
The scent, and often the shape of the flower, is specific and attracts a specific specie of euglossine bee (of which there are about 180).
Ophrys flower-pollinator relationship:
The remarkable insect-like flower of the Ophrys flowers do not produce nectar or utilizable pollen. They imitate the female wasp or bee both in appearance and scent. The powerful scent, similar to that of the sexual pheromone of the female, attracts male insects over a long range and, in the attempt to mate with the flower, pollination takes place. So powerful is this attraction that in controlled experiments male insects actually preferred the Ophrys flower over the female insect.
Flowers pollinated by butterflies and birds do not have a well developed scent because they rely mostly on colour or nectar to attract their pollinators.
TRANSMITTING SCENT IN HYBRIDISING
Disa breeders believe that fragrance is inhererited only maternally (through the pod parent) rather than the pollen parent.
In Paphiopedilum fragrance can be transmitted by the pollen. Paphiopedilum delenatii smells like citrus blooms and Paphiopedilum malipoense has a very powerful raspberry fragrance.
They are the two most fragrant Paphs in the Parvisepalum section.
Some clones are more heavily scented than others, especially in the morning when the sun first reaches the bloom. Crossing these two (Paph Lynleigh Koopowitz) produced a pleasant fragrance of raspberries.
Paph Wossner Jade (malipoense x niveum) produced only a limited number of fragrant offspring.
The fragrance of Paphiopedilum emersonii is compared to a mixture of chocolate and a freshly turned compost pile ! When Paph. emersonii is bred with Paph. delenatii to create Paph. Joyce Hasagawa a powerful old-fashioned rose scent emerges – In this case, mixing the fragrances from these two species creates a desirable fragrance quite unlike either of the parents.
Paph. kolopakingii has an intense scent of honeysuckle.
The Cattleya alliance provides the greatest variety of scent of all the orchids. Hybridisation has extended the possibilities of fragrance to include scents of carnation and spice, lemon, orange and apricot, vanilla and rose. Not all clones of the same grex will necessarily have the same blend or degree of fragrance.
Rhyncolaelia (Brassavola) digbiana , native to Central America, is a wonderfully fragrant and handsome parent producing a strong lemon-like perfume. It is often used in complex Cattleya hybridising. The flower is not ready for pollination until fully opened and loses its scent when pollinated.
Rhyncolaelia glauca emits a rosy-floral scent.
Neofinetia falcata, which is fragrant during the day and night, awards most of its progeny with fragrance.
When we first smell an orchid flower we relate it to substances we have already identified such as rose, hyacinth, cinnamon or jasmine. With more experience of sampling orchid fragrances we begin to relate scents to a particular orchid species.
Publications dealing with the description and classification of scent impressions abound in the specialist literature. For this lecture’s purpose I am omitting the complex chemical names and will stick to a simple but effective classification.
Certain fragrances can be related to certain colours. The major colour groups are:
1. white floral image – a soft fragrance
The white-floral scents incorporate the very pleasing scent notes of jasmine, tuberose, orange flower, honeysuckle etc. These flowers really are white in the majority of cases and release their scent mainly during the late evening or night. Most are pollinated by moths which use the scent and white colouring as pointers to the flower.
2. rosy floral image – a sweet, rosy smell almost like Turkish Delight
The scent of cyclamen, lily of the valley, sweet pea and rose identify this group. Sunlight and warmth trigger scent production.
3. Yellow scents – strong, citrus-like freesia fragrance
4. brown scents – reminding of spices ; cloves, coriander; caraway and cinnamon
Typical scent of a carnation.
5. Green scents – a mossy, wet / forest scent
6. dark smells – mostly unpleasant; musty, stale-socks
Remember that orchid fragrances are in many instances combinations of different fragrant compounds.
It has not been long since judging fragrance in orchids have become ‘fashionable’, especially in the Western world. The biggest problems seemed to be to motivate the judges that this is a serious exercise and to remind them to be frequently aware of the fragrance of the orchids even when judging them in other categories ? Perhaps a lot of confusion and wasting of time can be avoided if plants are judged for fragrance only when they are specifically entered in that category.
Because this is such a new field , a lot is still trial and error and learning through experience and there is very little scientifically based data to go on.
The other obstacle is that fragrance is a very personal, individual experience ? it can never be truly objective. Because judging will never be uniform, it is important to select a well?balanced judging team selected from a wide variety of people to accommodate for most tastes.
It is a good idea to try and cover the plant in a certain neutral container, so that the condition of the plant or the flower does not influence one unwittingly.
A real problem in fragrance judging is the that orchids are not all fragrant at the same time. Simulating the orchids which are fragrant at night to be fragrant in the daytime, and the other way around is quite a headache! Perhaps the easiest solution would be to get a few judges who would be willing to judge fragrance at two different times. The owner of the plant would then have to indicate when he would like his plant to be fragrance? judged.
The ‘Science of Smelling/sniffing’ is quite controversial ? Some people believe that you need only to whiff the air above the flower (head?space).Others suggest a waving?and?sniffing action while another school believes that you have to stick your nose right into it.
There is a basic score-sheet that we have used on a few occasions in South Africa:
I think it is very practical and simple, yet comprehensive enough to evaluate fragrance in an efficient manner.
There are five characteristics that the orchid fragrance are judged by:
1. Intensity ? the strength of fragrance
2. Diffuseness ? can you smell it from a distance or only very close
3. Pleasantness ? how pleasant (or unpleasant) the fragrance is.
4. Elegance ? how well rounded and perfumistic the fragrance is ; chemical notes or thin fragrances will be marked down.
5. Instant appeal ? Do I like it and how much?
All characteristics are scored out of ten points (minimum zero, maximum 10), except pleasantness which is scored from? 10 to 10.
A maximum of 50 points is possible.
Any additional comments on the fragrance can be put down ? Some fragrances may be unusual and very interesting. Whilst not conforming to what we understand as beautiful fragrance, it may be noted as being unusual enough to be commended.
|Judging Fragrance in Madagascar.
The sweet nighttime fragrances of the beautiful orchids of Madagascar, like Angraecum xerophyllum, are quite different to the daytime ‘fragrances’ at the local market.
A FEW MORE EXAMPLES:
There is an abundance of fragrance in the orchid world. It is quite impossible to mention them all, but for interesting sake we will look at a few more.
When I walk through my own greenhouse, I experience a variety of fragrances ? the most prominent one must be that of
Maxillaria tenuifolia which smells overpoweringly like coconut and tropical suntan lotion.
Another fragrance that comes to mind is the interesting chocolate-peppermint fragrance of the Stanhopeas.
Because Stanhopeas use up a lot of energy to emit their very heavy perfume, the flowers only last one to three days.
Sometimes the specific epithet gives us a hint as to what to expect. The epithets aromatica, fragrans and odorata imply fragrance in abundance.
The spicy-scented Lycaste aromatica comes from Central America. The large, orange flowers last more than a month, being fragrant on warm, sunny days.
Lycaste cruenta has a less spicy, more floral fragrance that it passes onto its progeny.
Lycaste locusta has the colouring and scent of a granny-smith apple.
Thunia marshalliana has an orange fragrance.
In the Orchid Review of March / April 1993 Jo Kelleher mentions the profound effect smells have on humans . “Certainly I leave the greenhouse in a hurry when Eria hyacinthoides opens its deceptive dainty flowers because it gives the impression that something nasty has died underneath the staging.”
The orchid most well known considering aroma, the Vanilla, is not fragrant at all ? only when the seedpod is treated does the magnificent scent appear.
Bulbophyllum and Masdevallia generally have mushroomy/musty smells that appeal to their pollinators (and not really to the human nose!)
Masdevallia triangularis has a repugnant smell and may leave the tongue and nose with an unpleasant dumb sensation. On the other hand Masdevallia glandulosa smells deliciously of sweet cloves.
Angraecum distichum is a small plant and a lot of flowers need to be open at the same time for the fragrance to be detected ? It is more fragrant at night.
Zygopetalum intermedium has a rosy/lilac fragrance.
Calauthron bicornutum, a South American species, flowers almost year round. The large white flowers produces an unusual scent resembling a mixture of fruit and candies.
Even some of the popular Cymbidium may be fragrant
Cycnoches chlorochilon produces a penetrating jasmine fragrance.
Dendrobium anosmum perfumes the air with a scent of raspberries.
With smaller plants, like this Aerangis hyaloides, a lot of the tiny flowers need to be open at the same time for the fragrance to be deteceted by the pollinator.
A FEW INDIGENOUS EXAMPLES:
Diaphanante fragrantissima is very fragrant.
Cyrtorchis arcuata is sweetly scented at night.
Some of the Pterygodium are fragrant ? They mostly have a strong, pungent smell e.g. Pterygodium caffrum, alatum and catholicum.
Disa cooperi smells like cloves.
Most of the Satyrium are scented. Some of them has a sweet smell, like Satyrium neglectum
Others have a pungent smell (Satyrium odorum, stenopetalum lupulinum, bracteatum, muticum and erectum) while Satyrium foliosum smells like quinces.
Mystacidium capense and Mystacidium venosum emit a strong, musky smell after dark.
For us who have an interest in orchids, the most important aspect of fragrance must be that it is becoming a useful taxonomic aid -The complex compounds of the fragrances can be studied and used for species identification.CONCLUSION
One of the few fragrant Phalaenopsis, for example, is Phal. violacea. Two species have been known under the name Phalaenopsis violacea and have been referred to as the Borneo and the Peninsular Malaysia type.
The Borneo type, now recognised as the distinct species Phalaenopsis bellina, is more uniform in shape, size and basic colour. Both species have a sweet rosy-floral fragrance, but Phal violacea has an additional blend of cinnamon.
There are limits on how long we can look at a favourite beautiful bloom, yet the scent of flowers is with us constantly in the growing area.
The aspect of fragrance has already brought a new interest in greenhouses and at shows ,and even if this is just a passing fancy, at least it was a pleasant one.
Some more reading:
Fragrant Orchids – an excerpt from a book by Steven Frowine