Orchids

extraordinary diversity and behavior

Humans have been fascinated by orchids for ages. When we think about orchids, most of us visualize the flamboyant, exuberant, gaudy floral displays produced chiefly by tropical species or by the activities of avid orchid breeders. Fair enough, but…

All that flamboyance and showiness evolved because each kind of orchid flower is very complex and adapted to particular pollinators. Most of the pollinators are insects, but a few are pollinated by hummingbirds. Each kind of flower is visited, typically, in a very specific way by its pollinating animals. Although some orchids do not require a pollinator but, rather, simply pollinate themselves, the majority set seed after the visit of a pollinating animal. Different kinds of orchids offer different rewards to pollinators, usually nectar, but sometimes special oils or fragrances. Some reward-less orchids rely on fooling visitors, by just looking like they might have a reward and so attracting naïve insects, or (most famously) by looking like a female insect and fooling the male insects into trying to copulate with the flower.

Orchids have actually gone a bit crazy. There are probably over twenty-five thousand species; taxonomists are not sure just how many there are. But there are way more orchids than all the birds and mammals in the whole world, and more orchids than any other kind of flowering plant except perhaps the aster and daisy family. Although they are most common in the tropics, orchids can be found almost everywhere except Antarctica and the very High Arctic, occupying almost any habitat, including on other plants; one even lives entirely underground.

Southeast Alaska has its share of orchids: as near as I can tell, we have about twenty-six species in nine or ten genera (genera is the plural of genus, a taxonomic unit that clusters similar species together). The numbers are a bit uncertain because taxonomists often have differing opinions on how to demarcate the species and how to cluster them. In this space, I intend to introduce each genus that’s found in Southeast, with a bit of information about its name and its biology. Most of our orchids are not as gaudy as their southern relatives, but they share some nifty adaptations with their gaudier cousins. Because I like to know how things work, I’m including information on how the flowers function, that is, how they control the visits of their pollinators—which, after all, is what orchids are famous for!.

Before I launch a discussion of our orchids, it is useful to explain a few things that apply to all or most orchids. By doing so, repetition can be avoided or at least reduced. And, by the way, in case you were wondering, the name ‘orchid’ comes from the Greek word for testicle, because the bulbous roots of some species reminded someone of male gonads.

All orchids produce huge numbers of minute, dust-like seeds that lack stored nutrients for seedling germination and growth. Therefore all seeds depend on forming associations with particular fungi (mycorrhizae) that bring in nutrients from decaying organic matter or from other plants. Finding the right mycorrhiza is a chancy business, and most seeds just die. If a seed finds the right mycorrhiza and germinates, most orchids plants eventually produce green leaves that can photosynthesize carbohydrates, and thus they can live somewhat independently. But some orchids have no greenery and are forever dependent on their mycorrhizae.

I will spare you (and me!) the fine details of the intricate arrangements of orchid flowers, which can be bewilderingly complex. But I will mention one very peculiar and mysterious thing: while an orchid flower is developing, it often (for some odd reason) rotates a hundred and eighty degrees on its axis, so what was up is now down. That is rather mysterious in itself. In one species of the genus Malaxis (at least in the European populations of a species that we have in our area), however, the rotation is a full three hundred and sixty degrees, so what was up is again up. I find this most peculiar—if the goal is to have ‘up’ be ‘up’, why rotate at all? Darwin noted this, and then, to confound all logic, saw that the ripe seed pod UNtwisted itself by three hundred and sixty degrees. Very peculiar. And all of that begs the question: Do those that twist only a hundred and eighty degrees also untwist when seed ripen?? It is all very strange!

Most orchids disperse pollen in clumps, rather than as loose collections of powdery, separated pollen grains (as in most flowers). The clumps of pollen grains are generally held together by sticky material and elastic threads, and sometimes several clumps are stuck together. The clumps are called pollinia. Although some other flowering plants (such as milkweeds) produce pollinia too, this habit is relatively unusual. When they pick up a pollinium, pollinators then carry many pollen grains at a time. This would seem to be very efficient, but actually the seed production of many orchids is limited by too-few pollinator visits.

OK, now for our Southeast orchids. I’ll start with the smallest and least conspicuous, dealing with each genus in turn, working up to some local beauties.

Listera. The genus is named for a seventeenth century English naturalist (Listera). These diminutive plants are known as twayblades, for the two broad leaves flanking the stem. There are four species in southeast, although two are rare. I have seen good numbers of two species along the rainforest trail near Bartlett Cove, and they should be quite widespread elsewhere in Southeast.

The nectar-bearing flowers are tiny, only a few millimeters across, and they are pollinated by equally miniscule insects such as dance flies, fungus gnats, or minute wasps. Darwin thoroughly studied the pollination mechanism of an English species of Listera, and ours apparently work the same way. When an insect touches a beak-like structure in the flower, a drop of very sticky liquid explodes from that structure, catching the tips of the pollinia and gumming them to the head (often the eyes) of the visiting insect. The sticky fluid hardens almost immediately, so the insect flies away with pollinia stuck on its head. After firing the sticky liquid and the pollinia, the female receptive surface (called a stigma) is exposed and ready to receive a pollinium from the next insect. When an insect bearing a pollinium on its head visits a flower whose stigma is exposed, the pollinium contacts the sticky stigma, so pollen is pulled away from the insect and pollination occurs. For all of this to happen, the beak-like structure actually moves, first to put the pollinia in position to be picked up by the exploding drop, and then to expose the stigma so another insect can deposit pollen.

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frog orchid. Photo by Bob Armstrong

Coeloglossum. The genus name means ‘hollow tongue’; I have not learned the source of this name; one idea was that it derived from the spur that holds nectar, but since this is shaped like a tiny sac and is not at all tongue-like, this name is puzzling. The common name is frog orchid, but it doesn’t look like a frog (to me), so that name is also a puzzle. This is reportedly a short-lived species, able to flower during its first year above ground and seldom living more than about three years. The flowers can be pollinated by small insects of various sorts, but details of how the flower works are not available; self-pollination is possible.

I’ve seen frog orchids on Gold Ridge, where they are not common. Although they can apparently produce many greenish flowers on each stem, the ones I’ve seen have all had only a few flowers on each short stem. These plants on Gold Ridge are at risk by being trampled by the many visitors that walk above the tram.

Malaxis. Once known as Hammarbya, the newer name of Malaxis comes from a Greek word meaning soft or softening, referring to the soft leaves of some species. The common name is, sadly, adder’s mouth orchid or adder’s tongue. Someone must have thought the flower resembled the front end of a poisonous snake (it takes a very unusual imagination!). There are two species in Southeast, mostly in bogs.

The tiny (less than two millimeters) flowers are yellowish green. They have nectar and a sweet odor, which attract very small insects, such a fungus gnats. Darwin studied one of our species, which also occurs in Eurasia. He observed that a sticky drop holds the ends of the pollinia, and when an insect enters the narrow opening of the flower, it runs into that sticky drop and pulls out the pollinia (on lower, front part of its thorax) when it flies on. When the insect then enters the next narrow flower, the pollinia are pulled off, in contact with the stigma. Apparently this species does not self-pollinate but requires an insect to bring pollen from another plant of the same species, achieving cross-pollination; however, the second species in our area may often self-pollinate.

Malaxis orchids reportedly have the peculiar but useful habit of vegetative propagation by means of little bud-like structures on the leaf tips; these little structures can sprout and grow into new plants.

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Dance fly in a coralroot orchid blossom. Photo by Bob Armstrong

Corallorhiza. There are two species of these coral-root orchids in Southeast. Both names describe the appearance of the roots, which are thought to look like branching corals. Both species produce fairly tall flowering stems with multiple flowers, either pink or yellow. Both lack any green pigment, so they cannot produce their own carbohydrates and are therefore dependent on their mycorrhizal associates for nutrients.

Both species are visited by small insects, including flies and wasps and bees, that can carry some pollen from plant to plant. However, most seeds are apparently produced by self-pollination, without a visit from an insect bringing pollen from another plant.

The pink-flowered species is often seen in conifer forest, but the yellow-flowered one seems to prefer more open, often deciduous woods.

Goodyera. The genus bears the name of a seventeenth –century botanist. The common name is entirely ridiculous; it is called rattlesnake plantain, although it has nothing to do with snakes of any kind nor is it a plantain. Because the leaves are sometimes mottled with white, some early pioneers may have been reminded of snakeskin and thought, by simple association, it could be used to treat snakebite. However, there aren’t many rattlers where our species lives, so the name seems doubly foolish.

One species of Goodyera grows in our forests. The flowers are white, borne on a tall spike. Each flower is first male, with mature pollen, and then female, with a sticky, receptive stigma (this sequence is called protandry, or first-male). Internal parts of the flower rearrange themselves slightly to better expose the stigma after pollen is removed. Pollination is reported to be accomplished by bumblebees, which first visit the older, female-phase flowers low on the spike, depositing any pollinia they may carry. Then the bees move up the spike, reaching the male-phase flowers and picking up pollinia, on their heads or tongues, to carry on to the next plant. Thus, seeds are typically produced by cross-pollination between different plants.

orchid-Pam
Platanthera. Photo by Pam Bergeson

Platanthera. There are at least eight species in Southeast. Some produce white, very aromatic flowers, while others make greenish flowers, but all bear the flowers on an elongated stalk. These orchids formerly were classified as species of Habenaria, from the Latin word for strap or rein (probably because one of the main flower parts is flat), hence the common name of rein orchid; an alternative name is bog orchid (although some also grow in wet forests). The current genus name seems to mean ‘flat flower’, perhaps referring to the same flower part.

Bog orchids are pollinated by a variety of insects, some mostly by moths or both moths and butterflies, others probably by bees, some by small flies and mosquitoes, and some by almost any insect of the right size and inclination. Our white, aromatic bog orchid is pollinated primarily by moths, at night, and our green bog orchid may have several possible pollinators. Certain species exhibit regional variation in the length of the nectar spur, odor of the flower, and the type of insect pollinators, even within the same species.

Platantheras present nectar in a nectar spur, which is visited by a foraging and pollinating insect, when it enters the flower in the proper way, from the front, and encounters the sexual parts. But at least some species also produce small dollops of nectar on other parts of the flower, perhaps to increase the allure of the flower to insects that subsequently enter the flower in the proper way.

The pollination mechanism is simple: the insect shoves it head into the flower, reaching into the nectar spur, and bumps into the sticky parts of the pollinia, which then attach to the eyes or tongue of the insect. Although cross-pollination is usually the norm, many of them may simply self-pollinate, if no pollinator visits them.

Piperia. Named for an American botanist, two species occur here; they are widespread but rare. They are similar to and sometimes classified with Platanthera, but sometimes they are classified in their own genus. They typically live in open woods. The flowering stem bears a number of small, green or white flowers that are reported to be aromatic especially at night, when they are pollinated by moths. A visiting moth can poke its head and tongue a short distance into the flower, and pick up pollinia on the tongue; an older flower is more open, and a visiting moth bearing pollinia can insert its head far enough to deposit pollinia on the stigma. Piperias are thought to be chiefly cross-pollinated.

Spiranthes. As the name suggests, the flowers spiral up in a tall spike. The common name is ladies’ tresses, because someone thought the inflorescence looks a bit like a woman’s braids. The white flowers are pollinated principally by long-tongued bumblebees. As in Goodyera, the flowers are typically protandrous (first male, then female), and when nectar-foraging bees work their way up the spike, from older flowers to younger ones, the last flowers they visit stick pollinia onto the bees’ tongues. As observed in detail by Darwin on a similar species, the pollinia are attached to a sticky disc, whose stickiness is activated by the bee’s tongue as it passes through the narrow opening to the pool of nectar. When the bee’s tongue is withdrawn, the pollinia are pulled out. On older flowers, the internal parts of the flower have been rearranged slightly, widening the opening where the bee inserts its head and exposing the receptive stigma. Flowers are usually out-crossed, but when there are few pollinator visits, male and female phases of each flower may overlap more, and some self-pollination may occur if a bee does visit. There is one species in Southeast. A study of our species on Vancouver Island, B. C. found that flowers received abundant bee visits and set seed accordingly, but visitation rates and seed production have not been studied here, where bee populations may be less dense.

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Sparrow’s-egg orchid. Photo by Kerry Howard

Cypripedium. The genus name of ladyslippers or moccasin flowers comes from classical mythology. It refers to the foot of Aphrodite (or Venus), who was formerly called Kypris. Presumably an inventive observer imagined that the foot of a goddess of love might wear a floral slipper. We have at least one species (with white flowers), mostly in open woods in scattered locations, and two others may creep in to the northernmost part of Southeast.

Ladyslippers have no nectar, but they are often aromatic. The flower acts like a trap. When a small bee enters the pouch-like slipper, it cannot get out the same way because of the slippery sides and in-rolled margin of the pouch. So the bee has to exit through the upper part of the flower and, in so doing, it passes by the sexual parts of the flower. In general, Cypripedium pollen is very sticky and readily adheres to the crawling bee, which picks up pollen as it leaves the flower. When the bee enters and exits another ladyslipper, it encounters the female parts first, brushing off pollen on the stigma.

Some species of ladyslippers can become dormant for as long as three to five years, not showing above-ground shoots at all during that time. Prolonged dormancy can be induced by stress, perhaps from a bad growing season or the cost of making many seeds. These dormancy periods sometimes presage mortality, but in other cases, the shoots come up again and the flower blooms after its rest period.

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Calypso. Photo by Bob Armstrong

Calypso. The common name of fairyslipper was no doubt inspired by its delicate and lovely shape, suitable perhaps for an ethereal, light-footed creature. The genus name comes ultimately from the Greek word for concealed and more immediately from the mythological goddess, Calypso. She was a beautiful nymph that lived in the forest. According to Homer’s Odyssey, she found Ulysses (Odysseus) when he was shipwrecked on her island, and she kept him for seven years.

The showy, pink-purple flower, usually one per stem, is said to be very aromatic, but it has no nectar. Bumblebee queens are the principal pollinators. Naïve queens (with no previous experience with this flower) visit calypsos but each queen soon learns that there are no nectar rewards to be found there, although the aroma might suggest otherwise. Such pollination by deception is characteristic of many orchids. Supposedly the queen bees learn quickly, so many calypsos are visited only once, and pollen may be removed but not deposited on another flower. Some researchers suggest that the slight variations in color and aroma that calypsos exhibit might facilitate fooling the bees into visiting more than one flower and accomplishing pollination.

The bees enter the open flower but discover no nectar and then back out. When they back up, apparently they hunch their backs and if, on the back of the thorax, they carried a pollinium from a previously visited flower, it gets brushed off on the stigma. A little farther toward the front of the flower, the backing-up bees encounter the pollinia of that flower, which in turn sticks to the back of the thorax, to be carried to another flower—unless the bee has learned its nectarless lesson. Calypso flowers may last more than eight days if not pollinated, but they wither in three or four days if pollination was successful. Apparently, fruit productions in calypso is generally poor, reflecting a low level of successful pollination.

We have one species of calypso here. I have seen it rarely, mostly in open, relatively dry areas. It is a temptation to pick Calypso flowers when one finds them, just because they are so lovely. But that seemingly simple act is likely to kill the plant, because the little, plucking tug can break the extremely delicate roots. So please don’t pick them!

There you have our orchids, and a lovely array it is. It is best not to try to transplant them, because many are delicate, and some are rare, so they should be left where they find themselves naturally. We can enjoy them in their natural places.

Thanks to Mary Stensvold and Ellen Anderson, USFS botanists, who provided helpful consultation.

Parasitic flowering plants

trouble underground

When we think of parasites, we usually think of tapeworms, ticks, fungi, and assorted micro-organisms. But the world of flowering plants provides some interesting examples of a botanical version of parasitism, in which one plant extracts nutrients from another. We have two quite conspicuous and common kinds of flowering-plant parasites: hemlock dwarf mistletoe (Arceuthobium campylopodium) and northern ground cone (with the resounding name of Boschniakia rossica). Both of these species are entirely parasitic (or almost so). They derive all or almost all of their nutrients from their host plants and are unable to survive without a host.

You may have noticed the ‘witches brooms’ of gnarly, tangled branches that are the result of a mistletoe infection. The mistletoe alters the balance of growth hormones in hemlocks (and sometimes other species), causing the ‘brooms’. Male and female mistletoe plants are separate, with very small, inconspicuous flowers. Pollination is mostly by wind. When the seeds mature, they are discharged explosively; they are capable of travelling ten yards or more. Because they are sticky, they adhere to other branches or trunks and start new infections. This species has been reasonably well studied, because heavy infestations decrease the economic value of the timber.

 

The ground cone pokes up above ground in June. All we see is the cone-like inflorescence of tightly packed, brownish flowers; the rest of the plant is underground. Ground cone is commonly parasitic on the roots of alders, and sometimes other species, including blueberries. Various insects may visit the flowers and accomplish pollination; occasionally we have seen bumblebees probing the flowers. The seeds are minute and very numerous. The biology of this species apparently has not been studied in detail, as I can find no scientific papers on the subject, but the medicinal uses of this plant are reported to be many. We do know, from local observations, that bears frequently dig up and eat the underground base of the flowering stalk.

In addition, all orchids depend on their mycorrhizae (fungal associates) at least at some time in their life history. Some researchers consider the relationship to be mutualistic, with both participants gaining some advantages, and that eventually may be the case when the adult orchid develops green leaves and can provide carbohydrates to the fungus in return for soil nutrients. However, other researchers refer to mycorrhizal associations as a parasitism by the orchids on the fungi. This seems especially applicable in the case of orchids that develop little or no green tissue as they mature, so they can contribute nothing to their fungal associates. We have two species of the genus Corallorhiza (coralroot), one of which has no green tissue at all, while the other has a little and so can make some carbohydrates. They are both parasitic on fungi for all of their lifespans, but the relationships are even more complex: they can indirectly parasitize green plants through their fungi, which attach to the roots of trees and shrubs (which have their own mycorrhizae), and draw nutrients from those hosts.

Less well known are the so-called hemi-parasites, half parasitic and half independent. They have chlorophyll and can synthesize carbohydrates, but also commonly latch on to other plants and capture some nutrients from these hosts. We have a number of hemi-parasites among our local flowers.

The plant called yellow rattle or rattle box (Rhinanthus minor) grows in open areas at low elevations. This species is capable of parasitizing the roots of many other herbaceous species, including grasses. A single Rhinanthus plant can attach itself to the roots of several other plants. Some plants, however, are able to resist invasion by the roots of the parasite. Rhinanthus plants clearly benefit from the parasitic connections, growing and reproducing better if they are connected to a host. Some hosts, such as legumes, are better than others in providing the parasite with nutrients. In addition, the parasite can take up defensive chemicals, such as alkaloids, from the host, and thus reduce the risk of herbivory. The effects on the host plants are negative, because many of their nutrients are drained away by the parasite; parasitized hosts have decreased growth and reproduction; the negative impact is greater in some hosts than in others. There are indirect effects of Rhinanthus parasitism too: parasitized hosts have lower ability to compete with other plants in the community, and lower ability to recover from herbivory, which then affects the relative abundance of various species in the entire community.

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Photo by Bob Armstrong

There are three species of Indian paintbrush (Castilleja) in Southeast, but only one has been studied much, and those studies were conducted elsewhere. In general, members of this genus grow better, flower more, and resist herbivory better, when they are connected to a host plant. Legumes seem to be better hosts than other plants, and two or more hosts may be better than one. When a parasitic paintbrush plant dies and decays, decomposition is accelerated, and co-occurring species have increased productivity, which may counter the usual negative effects of the parasite to some degree.

The genus Pedicularis—the louseworts–has about five representatives in our area, which have not been studied directly, as far as I can tell. In general, the negative effects of parasitism by different species of lousewort may vary among host species, and different louseworts have different host preferences. Some louseworts are reported to have mycorrhizal associations too, collecting nutrients via the fungal connection in addition to the usual direct parasitism.

Clearly, the world of the parasitic flowering plants is complicated, and it gets more complex as more studies are conducted. All those pretty (and not so pretty) flowers are intricately involved with many ecological interactions, and what we see above-ground is only a small part of the story.