Species Orchid Society of

Western Australia (Inc)


Unusual and Surprising Orchids and their
Reproductive Biology
by Ken Jones


Orchids have some of the most unusual and surprising, as well as some the most sublime flowers of all the flowering plants. But, as the late Professor Julius Sumner-Miller would say "why is this so".
It is not accidental. Flowers primarily have only one purpose, that is, to attract a pollinator. While they are attractive to us, we are not part of the evolutionary process that has been going on for thousands of years.


Accepting that notion that beauty is in the eye of the beholder, for this article, I will focus on the unusual, sometimes bizarre but always interesting orchid flowers.
For those among us using the internet and social media, you will have seen images of some of the following orchid flowers. I thought that it might be helpful to find out a little more about some of these species, and if possible, why their flowers are the way that they are.


Let's start with the Monkey Face orchid. Dracula simia is a south eastern Ecuadorean and Peruvian species that occurs in cloud forests from 1,000 - 2,000m as a small sized, cool growing epiphyte. It has 10-15cm successively flowering inflorescence with large flowers resembling a monkey's face. A mature plant will have many racemes in flower at the same time

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One of the most recognisable, and unique features of a Dracula spp flower is a lip that resembles an inverted mushroom cap. For this reason, biologists suspected that Dracula orchids mimic mushrooms to attract pollinators, and that these pollinators are most likely to be insects that will at least spend, but most likely complete their life cycles on mushrooms. The majority of this genus have narrowly restricted distributions and are found in forest with very little or no external intervention.

 

Loreno Endara had always wondered what were the pollinators for these species, and why were those pollinators, most likely insects, attracted to the flower?
She wanted to understand whether there were differences in the pollinator frequency of widespread vs. narrow spread endemics, and studied Dracula species in the Los Cedros Biological Reserve where fourteen Dracula species are known.
After many hours of field work, she was able to confirm that small dipterans (flies) of the genus Zygothrica remove and deposit pollinia loads on the Dracula species studied. The Zygothrica flies (superficially similar to the fruit flies) complete part of their life cycle on mushroom surfaces, where they breed, lay eggs and in some cases they feed on mushroom tissues or yeasts that grow on the mushroom surfaces. Other Dracula species are pollinated by small flies in the same genus.


Another orchid flower with more than a passing resemblance to an insect (its pollinator) is the Bee Orchid, Ophrys apifera that closely resembles a female bumblebee in the act of visiting the pink flower. This species also has a pheromone that smells much like orange blossom.


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This mechanism has been developed by this orchid to attract its principal pollinator, the male solitary bee. The lip of this orchid's flower resembles a female of a species of solitary bee (Eucera spp.; hymenoptera; anthophoridae) sitting on the flower. Male solitary bees attempt to 'mate' with the female, and during this process, the pollinia are detached and adhere to the male bee which flies to the next flower where the pollinia are detached and adhere to the stigma.
However, in some areas (particularly in the UK), the solitary bee has become extinct, largely as a result of habitat distraction and the spread of other bees which have replaced them. The orchid has adapted and in many parts of the UK, is now self-pollinating. When the pollinia is ready, wind action blows it onto the stigma pollinating the flower. This process is called autogamy. But as we know, this evolution will only delay the inevitable decline and extinction of the species.


Western Australia has an orchid that also mimics its pollinator. Orchids in the genus Drakaea (Hammer orchids) use a combination of physical and chemical cues to attract their pollinator. The flowers of this orchid physically resemble female wasps in the genus Zaspilothynnus (Tiphiidae) and release a chemical that mimics a mating pheromone of the female wasp. As the male wasp attempts to mate with the flower, they make contact with the pollinia which adheres to their abdomen. When they go to the next flower, the pollen is transferred.

The Mediterranean terrestrial species Orchis simia and Orchis italica also resemble monkeys, although are more reminiscent of naked hanging little men. The appearance is of cute little bodies hanging from the flowers, which are usually grey, white, pink, purple or reddish.


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Orchis simia was first discovered in France in 1779 and can be found from southern England down to northern Africa and as far east as Iran.
It used to be a common orchid in UK but widespread clearing and de-vegetation since 1920 have made it much rarer and difficult to find.
It is a perennial and flowers from May until June each year. Like many of our Australian terrestrial orchids, it has two oval tubers from which its genus name orchis from the orchidaceae family is derived. In Greek, orchis is the word for testicle.
Now, it is only known from two locations in Kent and two sites in Oxfordshire. It was common in the Thames Valley about 150 years ago. Fortunately, Orchid italica is still widespread in the Mediterranean countries.


Pecteilis radiata, [Thunb.] Raf. 1836 (syn Habenaria radiata) is found in China, Japan, Korea and Russia in forest glades at 1,500 m as a small to medium sized, erect, cold growing terrestrial with small, ovoid or ellipsoid tubers.
It is known by the common name the White Egret Orchid and as the Fringed Orchid, Crane Orchid or Sagiso and is one of the most well known Japanese species. It has up to 3 showy white flowers as the photo on the following page illustrates The flowers are up to 4cm across.


Unfortunately, Pecteilis radiata has become endangered in the wild due to habitat destruction, and is not easy to grow in captivity.

 

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Fortunately, it can still be found in the private orchid collector's gardens, and in some non-urbanised mountain areas over 500m as well as in protected Japanese bogs where people are allowed to view the flowers.
A number of variegated leaf forms are in production. Some have white margins on the leaves while others have variegated leaves with yellow/green variegation. There is also a peloric flower form with the cultivar name 'Hishou' in Japanese. In this instance, the peloric form has the petals replaced by a further two labellums creating a stunning symmetrical flower. This cultivar is rarely seen outside Japan, and the species itself demands special conditions and attention if mature flowering plants are to survive in cultivation for more than one or two seasons. Fortunately due to the liberal production of new tubers each season, the number of plants is easy to increase.

 


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Caleana major R Bria a unique Australian species from Queensland to Tasmania. As the photo on the following page demonstrates, it strongly resembles a duck in flight.
It is widespread and common, and forms sparse vegetative colonies in open forest and heathland on gravel or sandy soil. Pollination is undertaken by male sawflies that attempt to mate with the labellum, another instance of pseudocopulation in endemic Australian species.
This and the following species rely on the beneficial association with a very specific mycorrhizal fungi often found with Australian terrestrial orchids.



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Paracaleana minor ( R.Br. ) Blaxell 1972 (formerly Caleana minor) is known as the small duck orchid and has up to seven flowers on each raceme. It shares habitat with and resembles the somewhat larger Caleana major. However, these plants are seldom noticed because of their small size.
The habitat occupied by this species varies between open rocky areas on sloping ground. Generally, it is found with other grasses and smaller trees.

 

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In common with Caleana major it is often found growing at the base of eucalyptus trees, and its flower too is structured for insect pollination, although some populations produce viable asexually set seed.
In Western Australia, we find the Hammer Orchids. The genus Drakaea, all species of which are endemic to Western Australia use pheromones and mimicry to attract their Thynnine wasp pollinators. What is even more incredible is that each of the nine or so species has a one-to-one relationship with a particular Thynnine wasp species.
All are to some degree endangered by habitat destruction that affects their pollinators which too are often highly localised populations. The orchid emits a pheromone that is similar to that of the female wasp, and when the male wasp attempts to mate with it, the hinged labellum pivots and brings the male wasp into contact with pollinia and stigmatic surface.


Drakaea thynniphila

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Spiranthes diluvialis Sheviak is another rare terrestrial orchid. Its common name is Ute lady's tresses, and it is found in Wyoming, Colorado, Washington, Utah, Nevada, Idaho, Montana, and Nebraska..
A perennial orchid, it grows from a fleshy tuberous root and has a stiff, upright stem 10-50cm tall bearing 7 to more than 30 small, ivory flowers arranged in two to four twisting rows resembling the braids (tresses) of a woman's hair.


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This species, like many Australian terrestrial orchids has a special relationship with mycorrhizal fungi. During periods of stress, such as drought, the mycorrhizal fungi allows the plant to survive underground for years at a time by providing the plants with water and nutrients. This species is found in low, sub-irrigated wet meadows with a somewhat alkaline soil.
This species is regarded as threatened due to habitat loss and degradation, and the increasing use of groundwater irrigation. Invasive weed species are also stressing this species.
Spiranthes diluvialis has an unusual mixed mating system with both self-pollination and insect pollination. The level of self-pollination is determined by the abundance or otherwise of pollinators visiting the flowers. Outcrossing is promoted by protandrous flowers (flowers in which the male reproductive organs mature before the female reproductive organs) and by acropetal movement of long-tongued bees on inflorescences. Male and female phases overlap, however, and flowers are fully self-compatible.
In their article in Conservation Biology, Sipes and Tepedino note that no autogamous or agamospermous fruit set was observed, indicating that a pollen vector is required for reproduction. Their observations showed that bumblebees (Bombus spp.) are the most important pollinators of this species. The implication for land mangers is that for the species to survive, pollinators and pollen-producing plants are essential in land use planning, and the effect of pest management programs on bumblebees and the availability of bee nesting habitat is also important. Maintenance of floral diversity is critical as other flowering species may support Spiranthes diluvialis pollination.
Elleanthus robustus (Rchb. f.) Rchb. f. 1862 is found in Mexico, Panama, Colombia, Venezuela, Ecuador and Peru. It is a large to very large, warm to cold growing terrestrial in wet montane forests at 660-3,100m. Closely related to Sobralia, this species has an erect, cane-like, simple, stout stem, and in spring, a compact, cylindrical, densely flowered inflorescence.


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Orchids in the genus Elleanthus are often visited by hummingbirds as the following photo shows, and apparently pollinated.

 

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The flowers of this and other species are brightly coloured, with brightly coloured flower bracts, tubular in shape, produce nectar but lack any scent to attract an insect pollinator. A number of species in the genera Cochlioda are also thought to be bird-pollinated. This might also explain the unusual dark blue-grey colouration of the pollinia of some of the species including Elleanthus capitatus. Generally orchid pollinia are yellow.
Coryanthes picturata Rchb.f. 1864 is found in Mexico, Guatemala, Belize, Honduras, Nicaragua, Costa Rica and Panama at 100-600m It is a medium sized, hot to warm growing epiphyte that flowers in spring and summer on a pendent, 80 cm single to five flowered inflorescence carrying fragrant flowers. It is one of the commonly named bucket orchids and is often found in conjunction with ants and may benefit from their presence

 

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This species and others in the genus have an unusual co-evolutionary pollination mechanism that involves a number of orchid bee species. The one to five flowers are borne on a pendulous stem that arises from the base of the tall pseudobulbs. An aromatic fluid secreted by specialised glands collects in the column of the flower, which has a spoutlike opening just below the pollinia. A male bee, attracted by the strong odour, falls into the flower "bucket," where it collects some of the fluid in its leg pouches. To escape, the bee must crawl through the narrow spout, and the pollinia adhere to the bee as it leaves the flower. The bee then uses the fluid in its courtship with a female bee and deposits the pollinia on the stigma of the next bucket orchid that it enters. This species is also one of the orchids that are described as litter-trappers, that is, they trap leaf litter and other detritus which provides nutrient to the plant.
Angraecum sesquipedale Thours 182 is the well-known, large-sized, hot growing species from Madagascar that in winter has 1 to 6 fragrant flowers. Found at sea-level to 100m on sloping tree trunks near the sea in a constantly hot and wet habitat. The waxy, long-lived, fragrant flowers were of interest to Charles Darwin who predicted that there would be a pollinator that could reach to the bottom of the up to 35 cm spur in the back of the flower to reach the nectary. His theory was proved with the discovery of a long-tongued hawk moth, Xanthopan morganii praedicta about 100 years later.


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There are many more unusual and striking orchids, and each has its own story to tell. Log onto the internet to see what you can find.

Cont. next month