Solstice and More

A trip to Cowee Meadows is always worth dealing with some broken or missing boards and a few flooded (sometimes ankle deep) sections of trail—a common occurrence after rains. Around the time of the summer solstice, the wild iris take over, with shades from pale lavender to deep, rich purple covering much of the meadow but leaving some room for buttercups, lupines, and the last shooting stars.

On the slightly higher ground, some stands of the wild rose were just starting to flower while others were almost finished. The big white inflorescences of cow parsnip made a good framework on the meadow edges. They were often occupied by dozens of tiny, slender flies, presumably sipping up nectar from the little flowers that comprised each inflorescence. Fireweed had yet to come, but the buds were promising.

A common flower, dotted in among all the others, is the chocolate lily or rice-root. The typical brownish flower smells fetid (unlike most flowers) and is pollinated by flies. The shades of brown vary: some are very dark, even reddish, some are mottled with green or yellow, and a very few are mostly yellow. Do the pollinators care?

Photo by Kerry Howard

The sprawling shore plant called oysterleaf is widespread in northern latitudes. Its flowers are normally blue, but rarely white, according to two field guides, but we found white-flowered individuals to be quite common. The flower is insect-pollinated in some regions but is said to self-pollinate in others.

Few bees were flying on this day, but they are probably the principal pollinators of iris (as well as visiting many other flowers). A small insect might enter the flower but would not be big enough to contact the sexual parts. A bee crawls into the iris flower over a drooping petal-like sepal (the true petals are smaller and upright), passing under a narrow arm that bears the stigmatic surface where pollen is received, and then under a rod-shaped, pollen-producing stamen on its way to the nectar deep inside the flower. Cross-pollination would happen if the bee visited more than one flower, but the flowers are reported to be self-compatible, so if a bee happens to pick up some pollen on its way out of the flower and deposit some on the stigmatic surface, a seed might be produced that way.

Photo by Bob Armstrong

An aquatic plant long known as Potentilla palustris (marsh cinquefoil) was always a bit of a puzzle to me, because most potentillas have yellow flowers and five petals but this one seemed so different, with its red- or purplish-flowers with six or seven petals. I’ve just learned that botanists have now recognized these and other differences by assigning this species to a different genus; it’s now Comarum palustre. The flowers are reported to have valuable pollen with lots of essential amino acids and lots of concentrated nectar, and they are visited by many kinds of insects.

In the muskeg at the start of the trail, we inspected the bog laurel flowers. When an insect (not too small) visits the flower and walks around on the petals of the open flower, the stamens usually spring up from their niches on the surface of the petals, potentially placing pollen on the insect. So we could tell which flowers had been visited. A visiting insect might also bring in some pollen from another flower, effecting pollination. Our inspection revealed that some aging flowers had no sprung stamens and presumably would not set fruit, but some fresher flowers had clearly been visited and might set fruit.

On the way through the woods down to the big meadow, the dainty little wintergreen called single delight or shy maiden presents its one little white flower to insect visitors, typically a bumblebee. A visiting bee rapidly shakes the anthers, which releases pollen for the bee to eat and collect. The flower is demurely held face-down as it awaits a bee, but if pollination occurs, the flower raises its head–no longer shy– as the fruit matures. We joke that it is now a brazen hussy. Here’s a link to that process.

All told, we found over sixty kinds of flowers, but we didn’t beat our record from a previous year of over seventy-five species. Still, not bad!

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Pollination tricks

Flowers are a plant’s way of sexual advertisement. They are evolutionarily designed to attract animals that visit the flower in hopes of collecting nectar or pollen to eat, inadvertently accomplishing pollination. Insects are the most common type of animal that provide this service for flowers, although some insect visitors are thieves, taking the food but without pollinating.

To accomplish pollination, the foraging insect, as it rummages around inside a flower, incidentally gets pollen on its head or body or legs from the male parts (called anthers) of a flower and accidentally brushes off the acquired pollen on a receptive surface (called a stigma) of the female part of a flower. Many flowers have the means of avoiding self-pollination (within the same flower or between flowers on the same plant) and promoting cross-pollination from another plant, which creates greater genetic variation among offspring, one of the chief advantages of sexual reproduction. But that’s another, long story, so here I’m focused just on some behavioral interactions of insects and flowers.

Flowers have evolved many ways of controlling the visits of their pollinators, so the insects enter the flower in a particular way that effectively removes pollen from the anthers and deposits pollen on a stigma. The variety of ways in which plants do this could be the subject of several books; indeed, Darwin wrote one just about The Various Contrivances by which Orchids are Fertilised by Insects.

I’m not about to write a whole book here, so I’ll just describe a few ways some of our local flowering plants accomplish pollination. Open, saucer-shaped flowers are available to most insect visitors. A rose, for example, produces anthers and stigmas right in the middle of a circlet of petals, and all an insect has to do is walk around in the middle of the flower, sipping nectar and casually picking up or depositing pollen when it happens to contact the anthers. Nothing to it! Almost any bug can do it.

Much more interesting and intricate mechanisms of pollination exist in our local flora. For example, twayblade orchids grow profusely in young conifer forests, such as in Gustavus or near Eagle Glacier cabin. The flowers are tiny, pollinated by very small bees and flies. When the insect seeks nectar, it triggers the explosion of a drop of sticky stuff that picks up pollen on its way out of the flower and sticks the pollen to the head or eye of the insect, where it is cemented. Some parts of the flower actually move apart in order to make space for the exploding drop and pollen to emerge and fasten to the insect. Later, when the insect visits another twayblade, the pollen is detached somehow and deposited on the stigma, sometimes leaving the congealed sticky blob behind on the insect. Darwin spent a lot of effort figuring this one out!

A very different pollination mechanism is used by lupines, which are pollinated by bees. The sexual parts are hidden away in a fold between two fused petals in the lowest part of the flower. A bee pries open the fold as it probes for nectar. When it does so, out pop the sexual parts, and pollen can be dusted on the bee or brushed off the bee onto the stigma. When the flower has been visited, the uppermost petal has turned from white to pinkish-purple. The color change is a signal to future bee visitors that the nectar is depleted and the bee should visit other flowers on the stem.

Louseworts, in contrast, hide the sexual parts in a little hood in the upper part of the flower. So a visiting bee has to get into the flower in a certain way, often wedging open the hood, in order for its body to contact anther or stigma. One of the louseworts in Southeast, however, does it differently, as described the next paragraph.

“Buzz pollination’ is one of the most interesting and common pollination mechanisms in our area. In this process, a bee (usually) lands on the flower and buzzes in a special way. Its major wing muscles are temporarily inactivated, and its body just vibrates very rapidly, repeatedly hitting part of the flower. The vibrations shake dusty pollen onto the bee’s body, to be deposited eventually on a stigma. (Obviously, this technique doesn’t work with sticky pollen). Buzz pollination is how shooting stars, tomatoes, blueberries, wintergreens, and many other flowers get pollinated. Buzzing may also contribute to pollination even in open, saucer-shaped flowers such as salmonberry and roses.

Bog laurel. Photo by Bob Armstrong

Bog laurels grace our muskegs with their pink, wide-open flowers. If you look closely at a young flower, you would see that the female parts are in the center. But the male parts consist of arched, white filaments leading from the flower center to small, dark blobs (the anthers) that are nestled in pockets on the surface of the petals. When a bee lands on the flower, the spring-loaded filaments straighten, raising the anthers, and shaking pollen on the buzzing bee. So you can tell if a bee has been there by looking at the position of the filaments (arched or straight) and seeing if dark anthers remain in the petal pockets.

 

I’m sure there are other cute tricks by which our local plants contrive to deliver pollen from flower to flower. See if you can find some!

Tricky flowers

Most of our wild flowers are wide-open structures, just letting all the sexual parts hang out. Think of nagoonberry or cloudberry, asters, avens, silverweed, wild roses, geranium, anemones, and so on—all of these just present the sexual organs to whatever insect happens to land there. The smaller flowers of angelica and cow parsnip and their relatives do the same, but present the flowers in flat-topped bunches, making a good-sized landing platform for a visiting insect. It is then a relatively simple matter for an insect to walk around, picking up pollen from one flower and carrying it to another. Columbine and fernleaf goldthread dangle the sex organs loosely, downward or outward, where a visitor just bumps into them, when in search of nectar deeper in the flower.

Some of our flowers, however, are a bit more complex, requiring a visiting insect to do a little work or behave in a particular way. In these species, the sexual parts are typically enclosed within the flower—concealed in various ways. Here are some examples:

Lupine. Photo by Bob Armstrong

Lupine: Bees pry open the flower, and when they depress the lowest, keel-like petal, out pop the stigma (to receive pollen, if the bee carried any) and the anthers (containing pollen to be deposited on the bee and carried to another flower).

Twayblade orchid: A visiting tiny bee or fly pokes into the miniscule flower, bumping into a projection that releases a sticky gob that pulls out clumps of pollen. The pollen is stuck onto the insect’s face or head until another flower is visited and the pollen is inserted there.

Violet: Down in the heart of the flower, the stigma is encircled by closed anthers, packed tightly together (the technical term is ‘connivent’—conjuring up mental images of conniving and scheming deviously (!). A visiting insect displaces the stigma, pushing it to one side and perhaps depositing pollen, and only then do the anthers open, releasing pollen to be picked up and carried away by the insect.

Bog cranberry. Photo by Bob Armstrong

Blueberry, cranberry, shooting star, wintergreens (and tomato): Although the flowers differ in shape, all depend on what is called ‘buzz pollination.’ A visiting bee vibrates certain flight muscles (and buzzes), which causes pollen to shake down on the bee. If the bee already had pollen on its body, from another flower, it is brushed off onto the stigma.

Bunchberry/dwarf dogwood: the tiny flowers are clustered together, surrounded by white, petal-like bracts. Ripe flower buds open suddenly and the anthers explode their pollen into the air or onto an insect, when a tiny projection on one of the four petals is triggered, perhaps by an insect.

Lady-slipper orchid/moccasin flower: These flowers are doubly devious. They offer no nectar to insect visitors, who nevertheless prospect around inside the ‘slipper’, in hopes of a reward. But once inside that slipper, they cannot get out—except by squeezing through a tight opening at the back of the flower, where the sexual organs just happen to be located, convenient for pollen deposition and pick-up.

Bog laurel. Photo by Bob Armstrong

Bog laurel: When the flower opens, the anthers are held in little pockets on the faces of the petals, with slim filaments linking them to the center of the flower. This species is normally pollinated by bumblebees: when the bee lands on a flower, the anthers spring out of their pockets and dust pollen on the bee. The springing mechanism is reported to be very sensitive, so perhaps even small insects, coming in search of nectar, can spring the anthers free, but it is unclear if the pollen would land on their bodies and if they would be effective pollinators.

All these clever little arrangements are a small sample of the ingenious contrivances for pollination exhibited by flowers in more southerly latitudes, about which whole books have been written. The world of flowers is far more complicated than one might expect.