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: 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.
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: 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.