|The Orchids (Orchidaceae)
| Above: The Lady's Slipper Orchid, Cypripedium calceolus. The genus Cypripedium contains 45
species found in temperate parts of Europe, Asia and America. Only Cypripedium calceolus is
found in Britain where it is critically endangered. The surviving population of these attractive
yellow/green-red flowers inhabits a well-drained North-facing slope on limestone soil. In European
populations, however, its preferred habitat is calcareous woodland and also open fens and
marshy grassland. These plants are typically 30 to 60 cm (12 to 24 inches) in height and each
stem ends in a flower spike bearing one or two, rarely three, of the large conspicuous flowers.
The large yellow 'slipper' of Cypripedium calceolus is unmistakable, making this orchid one of the
easiest to identify. There are three red sepals, though the bottom two are fused together and
hang vertically downwards, the top sepal is lanceolate (tapered) and often not twisted. There are
also three petals, the lower petal, called the lip or labellum ('lower lip'), is typically highly modified
in orchids, and forms the slipper in Cypripedium calceolus. The two lateral petals are reddish and
typically twisted in the Lady's Slipper Orchid.
See: plant bodies for a general description of terms like sympodial and monopodial.
Orchids (family Orchidaceae) are one of the two largest families of flowering plants (the other
being the Asteraceae). They are monocotyledons, like the grasses. Many are terrestrial, growing
rooted in soil like conventional plants, but many are epiphytes and grow attached to woody
plants. Typical of many monocots, the leaves are strap-like and parallel-veined, at least in
European terrestrial orchids.
Flowering plants are modular organisms, growing as repeating units called phytomeres. Each
phytomere consisting of a stem internode and node with leaf or leaves and bud(s) associated
with that node. (Nodes may bear leaves and are the visible joints or swellings in plant stems,
connected to one-another by longer segments of stem called internodes). Orchids may exhibit
the sympodial growth habit or the monopodial growth habit. In sympodial growth each node
grows so far, elongating at its tip due to the addition of new cells by the apical meristem, before
its apical meristem ceases activity. Growth is then resumed by a sub-apical bud, such as a bud in
a leaf axil (axillary bud) to produce the next phytomere. In monopodial growth a single apical
bud produces the entire stem, giving rise to a series of phytomeres connected in a chain.
Eventually growth ceases when the terminal shoot flowers. In both cases, growth of the shoot
system eventually stops when a phytomere gives rise to a modified flower-bearing shoot or spike.
The spike is a modified shoot system, as are the flowers borne upon it. In a flower the internodes
are extremely short and the 'leaves' of the nodes, which are now close together, form the various
floral organs - sepals, petals, stamens and pistil.
Floral Morphology and Pollination
See flowers for an explanation of technical terms like stamen, anther, filament, stigma, style.
Monocots typically have flowers whose parts are in groups of three, or multiples of three - they
are trimerous. Orchids are no exception. An orchid flower has a set of three sepals in the lowest
whorl, then three petals above these, three stamens and the pistil consists of three fused carpels.
However, these parts are typically extensively modified. One petal is highly modified and forms
the lip or labellum. In many orchids the flower twists through 180 degrees during development,
so that the lip, which is the modified upper petal, is actually lower-most.
Typically, only one of the three stamens develops to maturity. (Evidence suggests that the
ancestral orchid had 6 stamens, in two whorls of 3, the outermost of which is generally
suppressed completely). The other two form sterile and reduced staminodes which tend to fuse
with the pistil to form a structure called the column (gymnostemium). The filament of the fertile
stamen is also typically fused to form part of the column. Indeed, in all orchids there is some
degree of fusion between the stamen filaments and the style (recall flower structure: the pistil
consists of the ovary, style and stigma). Often the separate structures are no longer
distinguishable and we have a column. The pollen-producing anther of the one fertile stamen
extends beyond the column, forming the anther cap when it dehisces (splits open to expose the
pollen). In many orchids the pollen are not simply released as separate grains, but typically the
anther produces 2 to 8 pollen masses, called pollinia, in which the pollen grains are firmly held
together. (In British orchids we have two pollinia). Further more, each pollinium has a thin stalk or
caudicle, also produced, at least in part, in the anther. The caudicle may be made up of pollen
grains, stuck together, or it may be a translucent non-cellular or hyaline filament of a substance
The cypripedioids (slipper orchids) differ in that they have two fertile stamens joined to the
gynoecium (the female parts or carpel - developmentally actually three carpels fused together)
and the third developing into the large staminode which forms a flap hanging over the entrance to
the basin-like labellum or 'slipper'. Insects which slip into the slipper can only exit by crawling
underneath the staminode where they are fused into contact with the pollinia and/or stigmas.
Mycorrhiza, the fungi associated with orchid roots have already been mentioned. All orchids are
mycotrophic at some stage in their life, feeding off their fungal partner. This is the case when the
tiny seeds of an orchid, which contain very little food reserves of their own, germinate. The orchid
may exist below ground for the first few years of its life, feeding off the fungus. Some orchids, as
already mentioned, like the Ghost orchid continue to feed off their fungal partners when mature.
Many orchids are epiphytes, living in tree canopies, for example, and so have aerial roots. In
these orchids the roots are often photosynthetic, containing chlorophyll. The aerial roots are also
absorptive and must quickly absorb water when rain runs down the trunk of a tree. To assist in
this the roots have a whitish sheath of one or more layers of dead cells, forming a spongy and
porous material called the velamen (velamen radicum), although most terrestrial orchids also
have this tissue. Cyanobacteria have been reported to inhabit the velamen of some orchids and it
remains a possibility that they contribute fixed nitrogen to the orchid roots.
The roots of some orchids also have swollen storage organs, called tuberoids. (Tubers are
Some orchids, like the Lady's-Slipper, are very long-lived plants. The Lady's-Slipper puts out its
first green leaves 1 to 4 years after germinating and flowers first appear 6 to 10 years after
germination, existing until then as a green shoot with a couple of leaves. This orchid has been
known to live for 192 years; the aerial flowers dying off each season, whilst the plant survives as
a subterranean branched rhizome (rhizome = underground stem, more generally any horizontal
stem on or in the substrate). Each branch of the rhizome may put out a flowering shoot, so that
the number of flowers clustering together increases with age of the plant.
Orchid life-cycles are often complex, sometimes incompletely understood, but often follow several
themes. Orchids may exist entirely underground, for several years after germinating, obtaining
nourishment from mycorrhiza (fungi associated with the roots). A wide spectrum of extraordinary
relationships exist between orchids and fungi! These mycorrhiza may, in turn, obtain nourishment
by digesting decaying organic matter, or by parasitising other plants. Some, like the Ghost
Orchid, Epipogium aphyllum, have no or very little chlorophyll. The Ghost Orchid is essentially
leafless, hence 'aphyllum' though its leaves have degenerated into small non-green scale leaves.
This orchid survives by digesting its mycorrhizal fungus, it is mycotrophic (feeding on fungi)! This
orchid has no roots as such, only a coral-like white rhizome covered in sparse hairs. It depends
instead entirely on its fungal partner for nutrition.
The Bird's-Nest Orchid (Neottia nidus-avis) of woodland is similar in this habit. This orchid has
very little chlorophyll and no functional photosynthesis. It also feeds on its mycorrhizal fungus,
which in turn depends on certain species of tree from which the fungus obtains its nutrients. Thus
we have a chain of dependency, with the fungus obtaining nutrients from its partner tree, some of
which are then 'stolen' by the orchid. (See also parasitic plants).
Many terrestrial orchids have underground storage organs, Some have corms. Corms consist of
subterranean vertical sections of stem which are short and swollen with stored nutrients and
typically protected by dead outer leaves. Many have rhizomes, which are apparently absent from
those with monopodial growth habit. Many of the sympodial orchids have pseduobulbs. Bulbs
are made up largely of thickened leaf-bases, holding nutrients, make up the bulk of the structure.
The term 'pseudobulb' was applied to stem thickenings in epiphytic orchids, which store nutrients.
The name 'orchid' literally means 'testis' and refers to the pair of tuber-like storage organs found
beneath ground in many sympodial terrestrial orchids. One tuber is being exhausted, left over
from the previous year, whilst the other tuber is currently active in storing nutrients for the winter
period, but will become next year's withered husk as a new tuber takes its place.
Note on studying orchids and orchid conservation:
If you wish to study orchids in the wild then you need to know a bit about conservation. For
example, most wild plants and all orchids are protected by law in Britain and cannot be uprooted,
although parts such as individual flowers may be picked. However, the it is illegal to damage or
pick the rarer forms, such as: Lady's-Slipper Orchid, Red Helleborine, Ghost, Fen, Monkey,
Military, Lizard, Late Spider and Early Spider Orchids and a few other selected subspecies. Laws
may even apply to the landowner. It is also illegal to possess living or dead plant parts of some
The point is: know the situation in your locale or you may accidentally pick the only observed
specimen in decades, in the case of the British Ghost Orchid for example! With modern digital
cameras it is usually unnecessary to pick flowers in order to study them. If you wish to examine
materials under a microscope then only pick what you need and only if the plants are abundant in
the area of study. Alternatively, visit your local herbarium or museum and examine dried
specimens. Museums generally accommodate curious visitors. Some have provision for visitors to
arrange to see parts of collections.
External links of interest
Above: the columns of two helleborines. Top - Epipactis helleborine (subpecies neerlandica)
illustrates the typical structure of the gymnostemium in cross-pollinated helleborines: a, anther
cap; r, rostellum; s, stigmatic surface; v, viscidium. The spotted mass represents the pollinia.
Bottom: Epipactis renzii shows the classic self-pollinated column structure. The rostellum is much
reduced and the viscidium absent.
Deceiving pollinators and other pollination mechanisms
Some 60% of orchids are pollinated by bees and wasps. This may be how orchids evolved before
some switched to alternative pollinators. Some orchids produce sugary nectar to attract and
reward their pollinators. For example, the Common Fragrant Orchid, Gymnadenia conopsea, has
a long spur - a conical vase-like extension at the base of the labellum which hangs down
beneath the flower. Only insects with a long-enough proboscis can reach the reward, such as
certain butterflies, which become the partially-specialised pollinators of this plant. To reach the
nectar which collects in the bottom of the spur, the insect lands on the labellum and then reaches
into the centre of the flower, far back to where the opening of the spur lies at the back of the
labellum. In the process, the insect brushes the rostellum and picks up the viscidium and pollinia.
The scent of the fragrant orchids and the vivid purple-pink colour of their flowers clearly serve to
attract pollinators. One tropical form, the Comet Orchid (Angraecum sesquipedale) is so-called
because it has a long tail-like spur, up to 30 cm (12 inches) in length. These flowers are only
pollinated effectively by the moth Xanthopan morgani which has a proboscis 30 cm long, so only
it can reach the nectar!
Above: two forms of Epipactis helleborine (the
Broad-Leaved Helleborine), a cross-pollinated
helleborine. This plant is quite variable, existing
as a number of varieties or subspecies. The lip
is divided into the cup-shaped hypochile at the
base and the heart-shaped epichile. The
epichile is broader than long and has two rough
protuberances or bosses at its base. The
variety on the right has bosses which are large
and fused into a V-shape.
Left: the cross-pollinating Epipactis atrorubens,
or dark-Red Helleborine. this can be
distinguished from Epipactis helleborine, by its
red flowers (the flowers of E. helleborine being
whitish-green). However, the colours of both
flowers vary greatly, especially those of E.
helleborine and it is wise to check additional
characteristics when confirming an identification.
For example, in his botanical key, Stace makes use of the fact that the ovaries (visible as the oval
or pear-shaped swollen structure at the back of the flower, behind the sepals and connecting the
flower to the flower stalk) is covered in many short pale hairs in Epipactis atrorubens, while
Epipactis helleborine has fewer or no hairs on its ovary. The rough highly wrinkled bosses on the
of the heart-shaped epichile is generally turned under (which is sometimes also the case with E.
Although the rich wine-red colour of atrorubens flowers is usually a give-sway, it should be
remembered that colour varies and some E. helleborine flowers are purple (they range from
green to dark purple). As its common name suggests, E. helleborine also has broader leaves, but
again there is considerable variation. These two helleborine can sometimes be difficult to tell
apart with certainty as all morphological features appear to overlap and especially when you
have unusual colour variants or dried specimens which have lost their colour.
These two orchids have different habitat preferences, though again with some possible overlap.
Atrorubrens prefers limestone and sunlit woods, whilst E. helleborine prefers deciduous
woodland, especially the better lit areas and beechwoods and is also found on limestone
pavements and dune slacks (depressions in dunes which are often damp). Often the habitat and
the presence of other plants of the same species can assist the identification of any odd
Epipactis helleborine is pollinated by wasps. The bosses guide the insect to push its head
in-between to reach the nectar which collects in the cup-like hypochile, brushing the rostellum,
rupturing the viscidium and picking up pollinia in the process. Epipactis atrorubens is also insect
pollinated and wasps, bees and hoverflies are the likely pollinator candidates. It is not unusual
with orchids to discover that the exact pollinators in some geographical regions remain unknown.
Left: the flower of Epipactis palustris, the by
its fairly large, projecting and circular
('orbicular') epichile which has a distinctly
frilly lip and is usually a vivid white and also
has a pair of yellow erect triangular lobes at
its base. The flowers are generally quite
large. The hypochile also has purple veins
on its inner surface. This is a
cross-pollinated plant, though
self-pollination possibly sometimes occurs.
The exact insect pollinators are not really
known. This orchid grows in fairly open
marshes with neutral or alkaline water.
Left: The Narrow-Lipped Helleborine,
Epipactis leptochila. This orchid is found in
deep woodland shade, especially in
ancient woodland and especially on steep
slopes with calcareous soils, such as
ancient beechwoods on chalk slopes. It can
be distinguished morphologically by its
narrow, arrow-shaped epichile, and small,
In pressed specimens, information on the angle of the lateral sepals is lost. These three orchids
are also notoriously difficult to tell apart, but with practise three distinct labellum shapes (at least)
can be distinguished, though there is considerable variation in each species. Also, the upper, and
less mature, flowers on the spike of densiflora can have labella that resemble those of borealis,
and further down they look more conopsea-like. It is therefore best to compare the lower more
mature flowers if possible. As the name suggests, densiflora has the most compact flower-spike
containing up to 100 flowers, and the stem and spike are often taller than the others. In contrast,
borealis has a more open and shorter flower spike, usually with 20-30 flowers. G. conopsea is
intermediate in height and flower number. However, specimens of borealis with more than 30
flowers in a full-looking flower spike do occur. The habitats of the three species may also overlap.
The answer is to use more than one characteristic when identifying Fragrant Orchids.
It is thought that the different labellum shapes in the Fragrant Orchids reflects different insect
pollinators. Butterflies and moths are known to be pollinators of Gymnadenia conopsea,
especially night-flying moths and the fragrance of the flowers increases at dusk. Information on
pollinators for the other two species is lacking.
Not all orchids are so generous with their rewards. Cypripedium calceolus, the Lady's Slipper
Orchid has an interesting pollination mechanism. It is pollinated by bees. The bee lands on the
edge of the entrance to the shoe-shaped labellum, or the shield-shaped staminode (sterile
stamen) visible hanging down at the entrance, where it is unable to gain a firm foothold. The bee
falls into the slipper and is unable to exit through the entrance, because of the recurved edges
and instead exits through one pr other of a pair of small openings, one on each side of the base
of the slipper, on either side of the column. Stiff hairs provide traction to facilitate the bee's exit
through these small holes. On its way the bee is forced past one of the pair of fertile stamens to
collect pollen in the form of a pollinium. (Each of the two stamens produces one pollinium). Upon
visiting a second flower, stiff papillae (tiny bumps) form a brush on the stigmatic surface which
collects the pollen. Only about 10% of flowers set pollen in European populations. What is the
bee's reward? Maybe the bees eventually learn that there isn't one and give up visiting these
flowers, or perhaps they receive shelter or oil secreted by the epithelial cells of the slipper. This
Orchid pollen seems, in general, not to be used by the pollinators as a food stuff. However, some
orchids offer pseudopollen, which looks like pollen, for the pollinators to eat. Bees have also
been observed collecting wax from orchids.
Some orchids excel in the art of deception, in particular those of the genus Ophrys. This genus
excels in mimicry. For example, the Bee Orchid, Ophrys apifera, has a beautiful labellum, the
sides and tip of which curve downwards, giving the labellum the appearance of a plump insect
abdomen. This plant lives for about 6 to 11 years. Pollination is largely by self-pollination in British
populations. The pollinia have flexible caudicles attached to the viscidia. These caudicles bend
about in the wind and soon touch the stigma. This mechanism is efficient. However, hybrids with
other orchids have been found, demonstrating that cross-pollination may also occur.
Pseudocopulation with bees has been recorded.
Pseudocopulation occurs when an orchid mimics the female of a specific insect species, attracting
males who attempt to mate with the flower and pick up pollen in the process. The flower attracts
the pollinator by mimicing the female in shape, colour and texture. The pattern of hairs on the
flower often mimics the pattern on the female insect. This is the case with Ophrys insectifera, the
Fly Orchid, which is actually pollinated by the wasp Gorytes mystaceus. The lateral petals of
Ophrys insectifera even resemble insect antennae!
It would seem that cross-pollination may dominant where the specific pollinator is abundant, but
that Ophrys apifera can fall-back on self-pollination if it is not. Indeed, in parts of its range where
suitable pollinators are rare, colonisation would be favoured by those individuals which can
Gymnodenia conopsea. Originally
comprised of three separate subspecies:
Gymnodenia conopsea conopsea,
Gymnodenia conopsea borealis and
Gymnodenia conopsea densiflora; it is now
grouped into three separate species:
Gymnodenia conopsea, borealis and
densiflora. These three subspecies can be
told apart by the form of their lateral sepals
Gymnodenia conopsea, the Common
Fragrant Orchid, thrives on chalk and
limestone grassland. The lateral sepals
bend down about 30 degrees and the
labellum is roughly as wide as long and
divided into three prominent lobes. The
middle lobe is as long as or longer than the
lateral (side) lobes. The flowers of G.
conopsea have a sickly-sweet scent with
rancid or acidic overtones.
In Gymnadenia borealis, the Heath Fragrant
Orchid (left) which is found on grassland
and heathland, the lateral sepals are short
and wise and somewhat spade-like and the
flower has a spicey-sweet clove-like scent.
The labellum is indistinctly lobed and the
central lobe is often the longest. The whole
labellum is longer than wide and somewhat
tongue-like or like a tube-dress in outline.
Gymnadenia densiflora, the Marsh Fragrant
Orchid, found in fens and occasionally chalk
grassland has longer lateral sepals with
parallel straight sides and blunt tips.
Characteristically, the lateral sepals are held
straight out horizontally, in contrast to those
of G. conopsea. The labellum of G.
densiflora is usually broader than wide and
flares out into rounded shoulders with
prominent lateral lobes. The middle lobe is
often much shorter.
Above: the Early Purple Orchid in early April, top and in mid-April middle
and bottom. Note the characteristic purple spots on the leaves.
pyramidal shape of the flower spikes of this orchid is due to the fact that,
as in many orchids, the flowers mature and open first at the base, last at
the apex. Note that in this specimen one of the basal flowers is already
beginning to whither, whilst many towards the apex are yet to open.
Above: Phragmipedium caudatum and its hybrids (such as Phragmipedium
x grande, the hybrid with Phragmipedium longifolium) is a tropical
American orchid. The petals are drawn out into long, narrow hanging
ribbons which may reach a length of 30 inches (75 cm) - about 3 or 4
times as long as those shown here. At first short when the flower opens,
they may grow at over 5 cm (2 in) a day!
The vast majority of orchid species occur in tropical and subtropical regions, though some are
found as far as the sub-arctic. Most of these more tropical orchids are epiphytes, growing
attached to the bark of trees. This enables them to obtain more light for photosynthesis. Many
root initially in soil and then after they have begun to climb trees their initial roots rot away and all
contact with the soil is lost (as in Vanilla). Mineral nutrition is then taken on by adventitious roots
growing out from the shoots (adventitious = growing in an usual position). In contrast, temperate
orchids are mostly terrestrial, that is rooted in soil throughout their lives and non-epiphytic.
Others grow anchored to the surface of boulders.
Epiphytes have access to limited nutrients - from rain water mixed with mineral dust and from
decomposing bark. They generally prefer trees with rough bark, as these are not only easier to
cling to but the furrows trap dust and moisture and encourage more rapid decomposition of dead
bark cells, releasing nutrients. Even so, orchids can only obtain sufficient nutrients from such
sources with the help of fungal symbionts. These fungi associate with orchid roots, penetrating
into the outer cell layers of the roots to form mycorrhizae. The fungus is kept in check as the
orchid's cells periodically digest the fungal hyphae. Fungi have a very large surface area to
volume ratio and a suite of enzymes, making them experts at obtaining nutrients from unlikely
sources. Some of these nutrients are supplied to the orchid in return, usually, for carbon
compounds fixed by the plant during photosynthesis. Terrestrial orchids also rely on fungal
partners. Some terrestrial orchids, however, cheat their fungal partners and provide nothing in
return, particularly if the same fungus obtains carbon from a third partner, such as a nearby tree,
and these orchids may lack the ability to photosynthesise altogether (see parasitic plants).
Orchid seeds are minute, superficially resembling grains of flour, and are called 'dust seeds'.
Each such seed weighs about a microgram. These seeds have practically no food reserves and
contain a loose-fitting seed-coat filled with air. This allows them to disperse far and wide very
easily, which is essential since the seed will not germinate unless it contacts its specific
mycorrhizal fungus first. This means that most seeds will never germinate, but orchid fruit (pods)
may contain thousands, or in some cases millions, of seeds so as to ensure sufficient numbers
find a suitable habitat. Only once the fungus contacts the seed, penetrates it and begins
supplying it with nutrients can the seed germinate. The orchid embryo is a relatively
undifferentiated and simple mass of cells.
Tropical ephiphytes may reach large proportions. The Scorpion Orchid (Arachnis flos-aeris) puts
out shoots many metres long and upright inflorescences (flowering stems) up to five feet tall.
Tropical orchids may be more diverse, but each species occupies a smaller range than many
temperate orchids whose distribution may span several continents. The flowers of tropical orchids
may also be large, especially on epiphytic forms, often measuring several inches across. In
tropical terrestrial forms which dwell on the shady forest floor, the flowers are often small, with the
leaves displaying patterns of bright colours possibly taking over the role, in part, of attracting
Epiphytic forms typically consist of a stem or rhizome which puts out adventitious roots which may
also contain chlorophyll. Indeed, in some forms there is no vegetative shoot system or leaves,
with the body of the orchid consisting entirely of green roots which put out inflorescence shoots.
The rhizome typically bears water-storing swellings called pseudo-bulbs. A pseudo-bulb may
consist of one swollen internode and accompanying node, or several internodes and nodes and
may vary in size from strings of minute green dots to structures 3 metres or more in length. The
pseudobulbs may be photosynthetic and the leaves are then reduced to small scale leaves. The
pseudo-bulbs swell when filled with water and shrivel when their reserves are depleted only to
swell again when it rains. As epiphytes have no contact with soil they must be able to collect
rainwater as it runs down the stem of their host, in which case the ability to store water surplus to
immediate requirements is vital to endure periods of prolonged dryness. The leaves may also be
fleshy and act for water storage, sometimes totally replacing the pseudo-bulbs in this function.
Orchids have no primary or tap root. Instead the rhizome puts out a number of secondary
adventitious roots of equal prominence. They are perennial plants, usually putting out new
shoots each year. These shoots are determinate in growth - they only grow so far in one
season before whithering. In some cases, however, they are indeterminate and persist for
several years and reach several metres in length, putting out new adventitious roots at intervals.
Some epiphytic orchids produce an extra type of root, which grows outwards and branches
profusely, forming a basket structure. These root baskets serve to catch falling leaves which
then decompose and provide the epiphyte with valuable nutrients.
Orchid leaves are often typical monocot leaves - having several parallel veins along their length
and are often strap-like. Deciduous orchids tend to have broader leaf blades, presumable to
maximise photosynthesis in their short season before falling in the dry season to conserve water.
Others last as long as 15 years and tend to be narrower and more strap-like. Some have
cylindrical leaves, some have fleshy leaves for water storage and some have scale leaves. Scale
leaves are common in forms in which the stem (rhizome or pseudo-bulbs) or roots have taken
over the role of photosynthesis and in non-photosynthetic saprophytic and parasitic forms. One
Bulbophyllum in Borneo has been recorded with leaves measuring 18 inches (45 cm) in diameter
and 24 inches (60 cm) in length!
The vast majority of orchids produce capsular fruit with dry seeds. The ovary is often 6-ribbed.
Typically many small seeds are produced, for example, each fruit of Epipactis leptochila contains
1000 to 2000 seeds. The orchid fruit (swollen fertilised ovary )is usually a three edged or ribbed
capsule; the edges corresponding either to the margins of the developmentally fused trio of
carpels or their midveins. The ovary (gynoecium) in orchids is inferior - it is enclosed by tissue
with the stamens and petals emerging above it. In some forms it is still divided into three cavities
or locules, with axial placentation; in others the central column has disappeared as the three
locules have merged into a single chamber with parietal placentation. Thus it sits enclosed in the
pedicel (flower stalk) and swells following fruit set to form the capsule. These capsules, some of
which are as large as a hen's egg, split along each carpel in three or six places into valves when
dry (they are dehiscent fruit). These valves remain joined to one-another at both ends by
filaments, such that they form shakers from which seeds are gradually scattered. Hygroscopic
hairs (fine filaments), originally outgrowths of the inner capsule wall, are intermingled with the
seeds. The largest orchid fruit may form up to 5 million minute 'dust seeds'. The hygroscopic
hairs twist about as they moisten and dry with changes in atmospheric humidity, dislodging the
tiny seeds which are readily air-borne.
Diversity of Function in Orchid Flowers
The rostellum is not present in all orchids, being absent in the cypripedioids for example. The
rostellum is a modified part of the middle of the three stigma lobes (most orchids still have three
fertile stigma lobes, suggesting that the non-fertile rostellum is only an extension of the middle
lobe). In some orchids, such as Cephalanthera and Vanilla, there is no distinct rostellum,
however the middle stigma lobe does secrete sticky liquid. Insects brushing past the stigma, when
reversing out of the flower, pick up some of this glue on their backs and then touch the pollen,
picking up pollen or pollinia which stick to the glue on their backs, to be carried off to another
flower. Species of Cephalanthera produce no or very little nectar and rely on deceit to attract
pollinating, such as production of pseudopollen (a roughened yellow mass of tissue on the
labellum, for example in Cephalanthera damasonium).
In some orchids, such as Epipactis, the middle stigma has a definite extension or 'beak', the
rostellum proper, which secretes the sticky fluid, but otherwise functions in much the same way as
in Cephalanthera. In some orchids, the rostellum squirts out its sticky glue when touched by an
insect as the rostellum margins curl back to release the pollinia which fall onto the glue to be
carried off by the insect. In some orchids, such as Orchis and Dactylorhiza, the viscidium is
covered by a delicate sheath which is easily broken away by a passing insect to reveal the glue,
which is a spot or disc called the viscidium.
In Catasetum, the labellum produces some white fleshy tissue, a food reward for visiting insects.
However, the labellum contains two trigger antennae (thread-like projections) and if an insect
should touch one of these triggers then the viscidium, complete with the pollinia attached to the
viscidium by a stalk, is fired at the insect. The whole package that is removed is referred to as a
pollinarium. In many orchids all pollinia are removed in a single pollinarium, but in others each
pollinium can be removed separately (each attached to a separate viscidium).
Whereas orchids often have hermaphrodite flowers, as so far described, some have separate
male and female flowers which may be visibly different in shape (dimorphism). Male and female
flowers are then often borne on separate inflorescences and at different times (so as to
encourage cross-pollination between different plants) but are occasionally found on the same
inflorescence. Examples include Catasetum and Cygnoches.
Orchid flowers may be scented. Generally those with smaller flowers and also those which attract
carrion insects have the stronger aromas (and unpleasant in the latter case). Some orchids may
flower for prolonged periods of several months, whereas others bloom in a day, often
synchronising their flowering so that all the flowers in a region open on the same morning and
whither by nightfall.
The three stigmas, the upper surfaces of the trimerous pistil, are also modified in orchids. One,
the medial stigma, is often modified and elongated to form a 'beak' or rostellum. This has an
important role in pollination and is beneath, and ventral to, the anther cap. Orchids are famous
for their wonderfully diverse and 'ingenious' mechanisms of pollination.
Many orchids are insect-pollinated. The rostellum secretes a sticky stigmatic fluid, often visible as
a droplet or two droplets on the rostellum, called the viscidium (plural = viscidium). The insect,
on its way to reach potential nectar or pollen, brushes past the viscidium, receiving a sticky
coating on its back. In some cases the styles actively squirts sticky glue on the back of the insect
when it brushes past, in a reflex action (at the same time the sides of the rostellum fold back,
causing the pollinia to drop onto the glue). The insect then brushes past the anther cap, picking
up pollinia, the caudicles of which attach to the sticky glue. Alternatively, the caudicles of the
pollinia may attach to the viscidium (which is right beside them) when the anther dehisces, waiting
as a whole package to attach to the back of an insect. In some cases the viscidium is covered with
a lid/sheath or bursicle which is easily dislodged by the insect to expose the glue.
The insect will then carry the pollinia away with it (one or both in flowers with two pollinia,
depending on species and how close together the two pollinia are) along with the viscidium and
caudicles. During flight, the caudicles dry and bend as they do so, causing the pollinia to point
forwards. When the insect arrives at a second flower, the pollinia are picked up by the receptive
stigmatic surface (formed largely by the two lateral stigmas but perhaps also part of the medial
stigma) which pick up the pollinia as the insect brushes past. The stigmatic surface is often bowl
or cup-shaped to receive the pollinia. This elaborate mechanism helps ensure
cross-pollination, either between flowers on the same plant or between different plants. The aim
of cross-pollination is to encourage a mixing of genes (or alleles - copies of the same gene which
vary within a population) which strengthens a population by providing a greater mix of
characteristics, increasing resistance of the population as a whole to unfavourable conditions and
disease, and increasing evolutionary flexibility.
Some orchids are self-compatible, meaning that pollen from the plant is capable of fertilising
either the same flower or a different flower on the same plant (strictly fertilising the ovules).
Self-compatibility in flowering plants is under genetic control. Some orchids have secondarily
acquired self-pollination. Although this 'inbreeding' does not confer the advantages of
cross-pollination, it can be useful if a plant exists in a specialised and stable habitat to which it is
well-adapted (and in which introducing new characteristics may weaken the stock). It is also
valuable when pollinators are lacking, or when an individual colonises a new suite and so can
reproduce in the absence of partners. Asexual reproduction confers similar advantages, and
many orchids reproduce asexually, typically by fragmentation of the rhizome or by the detachment
of tubers which form at the ends of the rhizome (e.g. Anacamptis pyramidalis, the Pyramidal
Orchid). Orchids may be self-compatible without exhibiting self-fertilisation, usually meaning that a
physical prevents pollen reaching the stigma of the same plant, rather than a genetic barrier,
such as the elaborate mechanism we have already described.
A good example to illustrate many of the above points are the (British) helleborines, Epipactis
spp. The Broad-Leaved helleborine, Epipactis helleborine, is self-compatible but does not
normally self-pollinate. Epipactis purpurata, the Violet Helleborine, and Epipactis atrorubens, the
Dark-Red Helleborine, also cross-pollinate. However, some helleborines, like the Narrow-Lipped
Helleborine, Epipactis leptochila, is usually self-pollinates, though sometimes cross-pollinates. In
those that favour cross-pollination, the rostellum is well-developed, the flowers open more-or-less
fully and the viscidium is clearly visible and the pollinia form compact masses. In those that
self-pollinate, the rostellum is reduced and the viscidium, if produced at all, soon disappears. The
pollinia also soon disintegrate and fall upon the receptive stigma of the same flower beneath.
(Normally the rostellum comes between the pollinia and the stigma). Also, the flowers tend to open
less fully or remain closed (and are said to be cleistogamous) so that self-pollination can
complete inside the closed flower. Helleborines thus exhibit the whole range in characters from
cross-pollinate to secondarily evolved self-pollination. This is illustrated in the diagram below:
'It was like the desecration of the most beautiful garden that God had created
and which I now uprooted, tore down, packed up and sold. The commission
seemed to me like blood-money the payment of which I was now awaiting. But I
must confess that the thick bundle of bank notes - of a size I had never
dreamed of quite altered my opinion.'
Although no idyllic Eden, what with the biting insects and snakes, we do have the vivid scene of a
beautiful forest carpeted with exotic epiphytes bearing large and fantastic flowers being utterly
destroyed. To compound the disaster, many orchids simply did not survive transportaion (a
journey by sea lasting for months) and those that did would slowly waste away in cultivation since
horticulturalists did not know how to cater for the special needs of these specialist and often
fastidious plants. The cut flower industry has also taken its toll, however, many orchids escaped
persecution by being unsuitable, sometimes because they whither rapidly when cut, and are still
abundant in certain regions. However, industry brought about the decimation of large regions and
a dwindling of biodiversity as favourite forms were heavily targeted, often those with the largest
and most showy flowers. A good example of the damage commercial flower collecting can do is
the case of Peristeria elata, also called the Flower of the Holy Spirit since it has white petals
resembling a dove. It grows as an epiphyte in Panama and its popularity has placed it in very real
danger of extinction in the wild.
Many countries in Europe and also the tropics introduced legislation to protect their orchids,
however, this can be difficult to police, especially in the tropics. In Britain, for example, several
orchids are protected by law: the Wildlife and Countryside Act, 1981, makes the uprooting of any
orchid illegal, unless you own or occupy the land (or have permission from those that do). Certain
species are given extra protection, such that it is illegal for even the landowner to uproot them or
pick any part of the plant or to collect seeds and no part or product derived from them can be
traded and it is further illegal to own any part of these plants, either dead or alive (unless you own
the land of course). Orchids in this category include: Cypripedium calceolus, Cephalanthera
rubra (Red Helleborine), Epipogium aphyllum, Fen, Monkey, Lizard, Military and Spider Orchids. If
you have orchids on your land then it is prudent to check their conservation status before doing
anything that may damage them.
Tropical orchids have received a mixed fortune in more recent times. Europeans and North
Americans eventually worked out how to grow many of the species of commercial value and for a
time Britain was the largest exporter of tropical orchids, ironically exporting many back to the
tropics! More recently, however, tropical countries have established their own horticultural
programs and now export orchids on a large scale, and of course they can provide more natural
conditions for these orchids at lower cost. However, expanding populations and urban spread
continues to pressure wild populations and in the future many forms will almost certainly become
extinct in the wild, if not totally. Some more hardy and common forms will no doubt persist, but the
near-paradisial wild forest gardens where fabulous orchids coated tree, rock and floor in a
multitude of forms are probably destined to become a thing of the past. Alas! Let us hope enough
wilderness will be set aside and protected.
Above: the bee orchid (Ophrys apifera). There are about 30 species of Ophrys and a
number of hybrids and varieties. Each species is tailored to a particular insect pollinator,
which is always an hymenopteran (bee or wasp). The petals form two narrow (their edges
roll over) hairy appendages that resemble insect antennae. The labellum rolls over at the
margins to make it look like a fat insect body and is intricately patterned in the bee orchid:
there is a central dull orange, hairless, semi-circular area bordered by narrow
maroon-brown and pale yellow bands and the speculum, which is a broader band of dull
purple (U or H-shaped) bopunded by a pale yellow band. The pendulous pair of pollinia are
clearly visible. The thick appendage at the end of the labellum produces a special odour
that mimics the pollinator's pehromones in some Ophrys species.
Orchids and Humankind - Orchid Conservation
Many orchids are today threatened with extinction. In many cases this is due to habitat
destruction. For example, the Ghost orchid, Epipogium aphyllum, naturally occurred in oak and
beechwoods in the British Isles and was last seen in Britain in 1986. However, this
non-photosynthetic orchid can live underground for many years in between flowering events and
may still occur in this region. Unbelievably, the site where it was last seen in Britain is now a
commercial conifer plantation!
In many cases orchids have suffered destruction at the hands of collectors, particularly
commercial collectors. Britain first became the first major importer of tropical orchids. Collecting
orchids from tropical forests is not easy. Although large mammals rarely bothered collectors,
there were still snakes, biting insects and leeches to contend with. Rather than undertake hard
treks to locate one or two prize specimens, the strategy was to send out parties of local people to
collect everything they could. Most of what was collected was simply discarded as of little value
and only prize specimens were sold (the local people apparently had no knowledge of what was
deemed valuable to the traders). Whole trees were felled to collect epiphytes, often destroying
the orchids in the process! This unpleasant bit of history is well reviewed by Kupper and
Linsenmaier (1961) in their excellent book 'Orchids' (Nelson pub.) from which I take the following
quote from an early European commercial orchid collector:
Catasetum is unique in that the pollination mechanism is triggered by an insect
touching of one of a pair of antennae. This pollination mechanism was intensively
studied by Darwin. In some species, both antennae are symmetrical and equally is
by far the most sensitive, the right antenna being held back out of the way. The
detail of the column of this flower is shown below:
The pair of pollinia are attached, via elastic stalks, to an elastic strap called the pedicel. The
pedicel is attached, via a hinge, to a disc (the viscidium) which is covered in sticky 'glue'. The
pedicel is stretched tight of the projecting beak or rostellum of the column. The viscidium is
continuous with flaps of tissue that form part of the antennae bases. Gently touching the antenna
releases the disc which swings forwards on its hinge, under the elastic strain in the pedicel which
springs back to a straightened shape. As it does so, the whole pollinarium is fired forwards,
detaching the anther cap which covers the pollinia. It is launched in such a way that the sticky disc
always strikes the insect first, attching itself and the pedicel and its pollinia to the insect. The
structure may fire for a meter or so and has sufficient force to knock the insect off the flower (from
the orchid's point of view the insect has done its job and needs to move on!). Darwin ascertained
that it was not simply vibration or displacement of the antenna which triggered the disc release.
The mechanism remains poorly understand and may involve an active movement of tissue,
perhaps in response to an electrochemical signal generated in response to the touch.
Above: a floral diagram for a non-cypripedium orchid. (Based in p[art on the diagram in: Ronse
de Craene, L.P. 2010. Floral Diagrams - An aid to understanding flower morphology and
evolution, Cambridge University Press). The bract is in black, sepals in grey and petals in
white, including the labellum (lab). The black circle indicates the main axis. The arrow indicates
resupination - rotation of the flower through 180 degrees on the flower stalk or ovary (the
ovary may assume a twisted appearance in some forms) a process which occurs in most
orchids during development and which brings the labellum into the lowermost position (the
bract does not change position in this process and becomes adjacent to the labellum). S =
staminode; St = stamen (fertile); Sty = style. Style, stamen filament and staminodes at least
partially fused to form the column. A hood (dotted line) covers the style and stamen.
The upward-pointing arrow indicates the bilateral symmetry (zygomorphy) of the flower (one
plane of symmetry) running from the axis to the bract; superscript o indicates a staminode; the
ovary is inferior.
Above: a view under the hood, showing the hidden pair of petals and
the two pollinia.
Above and below: the Man-Orchid (Orchis anthropophora, formerly
Aceras anthropophorum) photographed at Darland Banks, Kent. This
orchid is endangered in Britain. It is aptly named as the flowers look like
little hooded people. Send your photos of British orchids to the
Zooniverse Orchid Observers project: www.orchidobservers.org. This
project will provide us with valuable data on orchid responses to climate
The curious shape of the Man Orchid flower serves an unknown
function. Clearly it must facilitate pollination, but little is known
about the pollination of these flowers. In Britain, ants and hover
flies have been observed with removed pollinia glued to their
heads. Fly-pollinated flowers generally lack the large colourful
flowers of bee-pollinated flowers. Though quite large, the flowers of
Orchis anthropophora are not brightly coloured. The colour is said
to be variably red to yellow-green. Observation of spikes in
different developmental stages suggests to me that the flowers are
redder when newly emerged, fading to yellow-green as they mature
(might this depend on illumination levels?). Interestingly, flies are
barely able to see red which probably appears grey or black to
them. What remains unaccounted for is the large size of the
labellum and its particular shape.
Man Orchids may live for up to 14 years after first emergence
above ground, though they may not emerge or flower each year.
Studies suggest that the half-life of these orchids (the time taken
for half a population of 'newborns' to die) is between 4.0 and 7.8
Above and left: Neottia ovata (Listera
ovata) the Common Twayblade,
so-called because most specimens
have two basal leaves (occasionally
three, with the third being smaller).
Pollination is affected by small insects
such as a ichneumon wasps, sawflies
and beetles. This accounts for the
small green flowers.
Conservation of man orchids in fragmented landscapes has proven problematic. The orchid
grows best on chalk or limestone grassland which is well-drained and moderately grazed. It tends
to become overcrowded and out-competed by other plants if grassland is undergrazed, but also
suffers if grassland is overgrazed. Roadsides, abandoned quarries and pits are another common
Suggested Reading and References
Orchids of Britain & Ireland, A field and site guide. Harrap, A. and Harrap, S. 2009. 2nd ed. A & C Black,
Hollingsworth, PM, Squirrel, J and ML Hollingsworth, 2006. Taxonomic complexity, conservation and
recurrent origins of self pollination in Epipactis (Orchidaceae). Current taxonomic research on the British
& European flora 27 Bailey, J. & Ellis, R.G. (eds) 27–44.
Julou, T., B. Burghardt, G. Gebauer, D. Berveiller, C. Damesin and M-A. Selosse, 2004. Mixotrophy in
orchids: insights from a comparative study of green individuals and nonphotosynthetic individuals of
Cephalanthera damasonium. New Phytologist 166: 639–653.
Cameron, DD, K. Preiss, G. Gebauer and DJ. Read, 2009. The chlorophyll-containing orchid Corallorhiza
trifida derives little carbon through photosynthesis. New Phytologist 183: 358–364.
JAKUBSKA, A., D. PRZĄDO, M. STEININGER, J. ANIOŁ-KWIATKOWSK and M. KADEJ, 2005. Why do
pollinators become "sluggish"? Nectar chemical constituents from Epipactis helleborine (L.) Crantz
(Orchidaceae). Applied Ecology and Environmental Research 3: 29-38.
Above: the red-green 'elven' flowers of
Neottia cordata (Lesser Twayblade) are
also pollinated by small insects, such as
flies and gnats.
The twayblades have an interesting
pollination mechanism. Landing insects
follow the nectar groove on the labellum
up to the rostellum. The rostellum is
sensitive to touch. In Neottia cordata, at
least, this sensitivity is due to three
sensory hairs or trichomes. When
touched by a pollinating insect, the
rostellum explosively squirts out glue
onto the insect's head, which dries in a
couple of seconds. At the same time
the margins of the rostellum curve back
to release the pollinia which fall onto
the glue. The startled insect flies off
with the pollen. The rostellum also
bends spreads flat or bends forwards
and downwards to cover the stigma to
prevent the same insect from
self-pollinating the flower. After a few
hours, the rostellum shrinks away to
expose the stigma, which may now be
sticky, to other insects carrying
potential pollen from other flowers or
Above: the flower of a generalised orchid. Note that many species are deceptive and the spur
frequently contains no or very little nectar.
The Broad-leaved Helleborine, Epipactis helleborine, left, has a few special tricks to enhance
pollination. It secretes nectar into the hypochile cup. Only insects of the right size or with the right
length of proboscis can easily reach the nectar, by inserting their proboscis in between the pair
of bosses at the base of the epichile. The principle pollinators are wasps. Self-fertilisation is
theoretically possible but is thought to be rare. However, there are reports of occasional
cleistogamy, in which the flowers fail to open in less favourable conditions resulting in crumbling
of the pollinia and self-pollination. More usual, however, appears to be geitonogamy in which
wasps cross-pollinate flowers on the same spike. The nectar has a narcotic effect on the
pollinators, making them 'drunk' which causes them to spend more time on the same flower spike,
which has been shown to increase pollination success.
Ethanol is one component of the nectar and it is suggested that wasps which have been feeding
on fruit contaminate the nectar with yeast which metabolisms sugars in the nectar to ethanol.
However, Jakubska et al. (2004) have pointed out that ethanol is highly volatile and it is doubtful
whether the concentrations would remain high enough to intoxicate wasps, especially since this
plant flowers at the height of summer. These authors carried out gas chromatographic analysis
on the nectar and found that it contains its own less-volatile narcotic agents such as
oxycodone, morphinans and indole-derivatives, which could account for the main narcotic effect.
Furthermore, several antibacterial and antifungal compounds were also detected, such as
furfural, syringol, eugenol, methyl-eugenol, xanthatin, furanone and indole-derivatives.
The nectar of Epipactis helleborine also contains scented volatile compounds and insect
attractants, including vanillin, furfural, ethanol and heptanal. Vanillin, which gives us vanilla
flavouring, was first extracted from the Vanilla orchid (but is now largely synthesised). The flowers
of Epipactis atrorubens also smell distinctively of vanilla and it seems likely that this is also due to
vanillin. It has been reported that Epipactis growing on open sunny dunes will turn its flowers to
face away from the midday sun (Watsonia 2005, 25: 289-298), which possibly prevents
over-heating of the flower and excessive evaporation of nectar volatiles.
Above: Epipactis helleborine
Above: a close-up view of the Early Purple Orchid.
Above: The Early Spider Orchid, Ophrys sphegodes. This is
a short-lived orchid, most flowering once and then dying,
but some living for up to ten years. This flower is pollinated
by the male solitary bee, Andrena nigroaenea: the flower
mimics the female and the male attempts to mate with it
(pseudocopulation) effecting pollination.