The various contrivances of orchids

I joined the local orchid society this winter.  The months of soggy dark require unusual coping measures at times; the displays of blooming orchids on the "show and tell" table at the monthly meetings alone are worth the membership.  My own little collection isn't doing too badly.  My phalaenopsis and paphilopedilum are blooming, and the zygopetalum's buds are swelling steadily. 

Phalaenopsis, known as the moth orchid.  Photo: J. A. Gervais

Orchids make up the largest plant family on the planet, with about 24,000 species.  They live in a staggering array of environments, from the tropical rainforests most of us associate with them to tundra environments, in the deep shade and out in the open sun, perched in trees or on the ground.  They are united, however, in their extraordinary biology, making use of an incredible array of other organisms to help them through their life cycle.

The local orchid society has about thirty members, small enough that guests are immediately recognized as such and welcomed with enthusiastic delight.  How do you not join a group of people who love to talk about flowers?  The skill level ranges from experts who hone their skills cultivating the most challenging plants, to people like me who can kill just about any orchid effortlessly.  I suspect the experienced growers look on us neophytes as a great way to clean out the clutter of their greenhouses: giving an extra orchid to someone who at least admires it seems less heartless than throwing it straight on the compost heap.  I view it as a type of symbiosis, although the plants may not.

Orchids have developed trans-species  interrelationships to a remarkable degree on several fronts.  The seeds require the services of a mycorrhyzal fungus in order to germinate, relying on the fungus to make up for their lack of endocarp.  Many species are epiphytes, perching on the trunks and branches of larger plants.  The pseudobulbs of other orchids harbor ferocious ants that offer protection to their hosts.  Most noteworthy, some orchids have developed extraordinary coevolutionary relationships for pollination.

Anagraecum sesquipedale.  Charles Darwin hypothesized that this magnificent orchid is pollinated by a hawk moth.  The moth, Xanthopan morganii, wasn't discovered for another 41 years, and proof of pollination services had to wait 130 years after Darwin's insight.

Although many flowering plants have built relationships with animals for the purposes of both pollen delivery and seed dispersal, orchids have gone to extremes.  The pollen of the vast majority of plant species is released as a dust of individual grains, but in nearly all orchids pollen is wadded up into two to twelve waxy balls, called pollinia.  It's a high-risk strategy, because each flower on the plant (and many produce only a single flower) has exactly that many chances to fertilize another plant's flowers for seeds.  It's a twist on putting all of one's eggs in a very few baskets.

The pollinia are designed for long-distance transit.  Pollinia on hawk moths in the wild have remained stuck in place and ready for deposit for over three weeks.  Insects, birds, and moths that visit orchids may have multiple pollinia stuck to their heads, beaks, and proboscuses like yellow bunny ears.  Different species of orchids place their pollinia in slightly different positions on the pollinator, ensuring correct delivery when the animal visits the appropriate orchid species again. 

This trait can be quite useful for someone interested in propagating orchids, and in creating new hybrids.  It isn't hard to use a pencil or other pointed object to lift the pollinia free of the flower column; they will quickly bind tightly to the object and orient themselves for maximum contact with the receiving flower's stigma.  It is a system easily manipulated by people.  In fact, we're the only mammal that pollinates orchids.  Once fertilized, the flowers quickly wilt.  This, announced my high school biology teacher with a wicked grin, opens up interesting possibilities if you don't like the prom date to whom you are expected to offer an expensive orchid corsage.

The flowers are all about sex, as all flowers are, but for some orchids it's a double entendre.  The sneakiest orchids are those whose flower parts have evolved to resemble female insects, complete with a release of chemicals that mimic the insects' own pheromones.  The strategy is known as pseudocopulation, as the befuddled male insect attempts to copulate with the flowers, and gets tagged with a pollinium for his pains.  Presumably he either doesn't learn, forgets quickly enough, or becomes desperate enough to visit another orchid of the same species before he dies.  The odds are long, and because of that the flowers remain intact for many weeks.  This is, of course, one of the characteristics that makes them so irresistable to humans bent on romance. 

The aptly named bee orchid, Ophrys apifera.  It is pollinated by male bumblebees and is an example of pseudocopulation.  Photo by Nancy Cottner

Not all orchids try to forgo paying the pollinators for their services through deceit.  Many offer nectar, which varies in sugar concentration depending on the pollinator. Specialized avian pollinators such as sunbirds earn the highest reward; hawk-moth-pollinated flowers offer a somewhat lower sugar level, and the least concentrated nectar is payment to the least-specialized pollinators from the more generalist orchids.  Within the flower, the most concentrated nectar is the farthest in, encouraging a good push to obtain the reward, and maximum contact with the pollinia.  Other orchids offer scents or waxes and resins that are gathered by their pollinators.

My fellow orchid enthusiasts range from generalists who do not seem to have ever met an orchid they didn't like, to those who specialize on one small subgroup.  Some folks seem taken up entirely by the challenge of the cultivation of the most exacting varieties, whereas others of us are unapologetic fans of the lowest-maintenance plants that reliably produce bright, interesting blooms with the least amount of fuss.  We're all in it for the flowers. 

For all their trickery and bribes, less than one in five tropical orchids typically achieves fruit set in the wild.  Pollination is generally thought to be the limiting factor for reproduction in wild orchids, even with their absolute dependence on fungi for seed germination.  Wild orchids are perhaps most amazing in the fact they exist at all, let alone having successfully woven themselves into the ecological fabric of so many places.

The orchids on the monthly show and tell table are often so hybridized by human breeders that the names of the crosses don't always fit on the plants' tags.  These are organisms of the greenhouse and windowsill, depending on the passion, space, and financial allocations of the owners.  I asked one of my fellow club members how many plants he had.  "Seven hundred, I think," he answered.  "I have two greenhouses now.  We all started with a few orchids on a windowsill."  Orchids have been amazingly successful at bending yet another species to the task of continuing their existence. 

I swear my little collection isn't going to need more space than my windowsills.  Soon, after the peas have sent up tendrils and the lambs have all been born, I'll be out in the woods hunting for my favorite orchid: Calypso bulbosa, which grows in heavily shaded understory, and tricks bumblebees into pollinating it.  I don't have to do anything at all, except admire it and the extraordinary ecological relationships that sustain it.  I don't think, however, that either the club members or their orchid masters have given up on me.

Calypso bulbosa.  Photo: J. A. Gervais

Sources:

Boyden, T. C. 1982. The pollination biology of Calypso bulbosa var Americana (Orchidacea): initial deception of bumblebee visitors.  Oecologia 55(2):178-184.

Cozzolino, S., and A. Widmer.  2005.  Orchid diversity: an evolutionary consequence of deception? Trends in Ecology and Evolution 20(9):487-494.

Darwin, C.  1882.  The various contrivances by which orchids are fertilized by insects. 2nd Edition, Revised. London: John Murray.

Micheneau, C., S. D. Johnson and M. F. Fay.  2009.  Orchid pollination: from Darwin to the present day. Botanical Journal of the Linnean Society 161:1-19.

Tremblay, R. L., J. D. Ackerman, J. K. Zimmerman, and R. N. Calvo.  2005.  Variation in sexual reproduction in orchids and its evolutionary consequences: a spasmodic journey to diversification.  Botanical Journal of the Linnean Society 84: 1-54.

Delphinium

I first noticed that they had all vanished along the creek bed near the road the first day of summer.  Farther up in the shadier parts of the forest, a few still linger, but their wrinkled, faded appearance suggests that they, too, will soon disappear.  Below the last faded flowers, fat pods are forming, swelling with the seeds of a spectacular display in the future.  The Delphinium flowers of the western Oregon woods belong to spring, however, and their season is now over.

I begin watching for Delphinium long before the buds have even formed.  The leaves begin pushing up in February, a welcome sign of spring after a long, dark, wet winter.  By April, the plants are beginning to form their buds, and the first flowers appear at the end of the month. 

Photo: J. A. Gervais

The flowers are a brilliant deep bluish-purple, a color so intense one friend remarked that it makes your teeth hurt.  They seem to glow, and I can only imagine what visual signal they send to bees and other insects that can see in the ultraviolet spectrum.  That incredible blue colors not only some of the petals but also the sepals, which form the star-like form of this flower and the long trailing spur that give this flower its common name, larkspur.  The true petals are small and held tight in the flower’s center.  The topmost petal arcs white in color, a bright flash in a field of midnight blue.

The genus Delphinium is large, with several hundred species currently recognized.  Individual plants growing in different places vary dramatically in size and form, and Delphinium species can hybridize with one another.  Keying them out often involves digging them up and studying their roots.  I’m pretty sure that the larkspurs growing along the shady creek banks in the forest above me are Delphinium trollifolium, but I haven’t dug one up to fully key it out.  I don’t need to know so much that I’m willing to murder a plant that each spring gives me such a marvelous gift.

Photo: J. A. Gervais

Hummingbirds, bees, and butterflies visit Delphinium flowers for their nectar.  The plants however contain an alkaloid compound that is highly toxic; although some insects use it as a host plant for their larvae, Delphinium has frequently been responsible for livestock poisoning.  Presumably, wild grazers learn to leave it alone.  So it grows locally in dense stands of stunning color, heralding in the growing season even when overcast and wet weather in western Oregon continues.  It may be raining, but there is still cause for celebration.

The flowers remind me of dark velvet stars, each with a comet’s tail trailing behind it as it leans out from the stem.  Or they might be little people, arms and legs outstretched in a joyous leap.  Flowers are structures evolved with the sole purpose of ensuring cross-pollination and the production of viable seeds.  Delphinium burst forth each spring to mark the renewal that arises only from the loss of those that came before.

Photo: J. A. Gervais

Trillium

Trillium chloropetalum, the sessile trillium or wake-robin, flowers in mid-March in the woods of western Oregon.  It blooms just before the start of the spring chorus of birdsong.  This plant's mottled leaves are  almost as showy as its greenish-white flowers, which don't open into broad showy blooms like the western trillium. Both species of trillium produce a seed with an eliasome, a fleshy body particularly attractive to ants who disperse the majority of the seeds.  Yellow jackets also disperse trillium seeds.  These plants are pollinated by beetles, bumble bees, moths, and the non-native honeybees.

I didn't find any published research on the sessile trillium, but the western trillium can live to be over seventy years old based on counts of the annual restrictions on its rhizome. It does not even begin to flower until its fifteenth year. Trilliums don't survive disturbances such as logging, and the increased numbers of mice associated with clearcut and edge habitat take a toll on their seeds.  Long-lived, slow-growing plants affected by human disturbance face an uncertain future.

Even so, the sessile trillium persists in some unlikely places.  Along the overlooked urban banks of a local river, a thin strip of trees between the pedestrian path and the water's edge ducks under a series of overpasses.  Scotch broom, English ivy, and Himalaya blackberry tangle old plastic bags, broken bottles, and other refuse in the understory.  Nobody looks to these places for conservation.  But sessile trilliums bloom here every spring, refusing to relinquish this patch of forsaken ground.

Trillium chloropetalum. Photo by Linda Hardie-Scott

They remind me of the hand-held candles used in protests and memorial services, the flame borne above a flimsy shield.  These past few weeks have been marked in the human world by much upheaval and anguish in many countries torn by civil war, government violence against the unarmed, and the disasters in Japan.  The Japanese ceremony of floating candle lanterns, Toro Nagashi, honors the dead.  The trilliums blooming in the local woods have their own purpose, but they are still bright spots of both hope and memory in these dark times.