(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:
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
benzyl acetate ( jasmine)
d-carvone ( rye bread)
methyl salicilate( wintergreen)
methyl cinnimate ( cinnamon)
eugenol ( cloves)
1,8-cineole ( Vicks)
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 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.
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
Lc Glad Tidings x Moochie
The Cattleya alliance provides the greatest variety of scent of all orchids. Not all the clones of the same grex will necessarily have the same blend or degree of fragrance. At an orchid meeting three seedlings of Lc Glad Tidings x Lc.Moochie were 'test'sniffed'. As literature suggested all three had distinctly different scents.
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 are quite different to the daytime 'fragrances' at the local market.
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.
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