As I sat here on yet another gray and drippy day in mid-January, grousing futilely and needing a cheering thought, there popped up a memory from my old life in the Midwest (probably prompted by recent reading). There are many things in the Midwest that I miss, and one of them is the deciduous forest with its many kinds of flowers in the understory; there are well over a dozen species. It’s a spectacular show in early spring (when my grad students and I did research on seven of them), and other species come along later on.
Many of these early species take advantage of the open canopy that lets in plenty of light before the trees leaf out. The light is used to make carbohydrates for energy (needed for growth and seed development) and a bit of warmth facilitates the activity of insect pollinators. Even the species that don’t flower until later in the season can build up stores of energy to be used at their proper time. I think that the availability of light is probably one of several factors contributing to the floral diversity in the deciduous forest.
All that made me think about our coastal rainforest, whose floor is mostly shades of green, lovely in its own way but scarcely as showy. Here in the coastal coniferous forest, the understory is always dark; the canopy blocks lots of light all year long. And only a few flowers thrive throughout the forest; several others are happier in somewhat brighter places on the forest edges or in canopy openings, although they are sometimes found scattered within the forest.
Whatever the reasons for the dearth of understory flowers here, I chose to contemplate the flowers that regularly decorate the forest floor. They are little points of delight, good to envision on dark day even though their blooming time is still months away.
–bunchberry or dwarf dogwood: very widespread in the forest, the four white bracts around a central cluster of small flowers make a good showing. The flowers release pollen in an unusual way: by a special catapult mechanism that throws the pollen up several centimeters. The flowers open elastically, explosively, and extremely rapidly (in less than a millisecond), flipping the pollen-bearing anthers upwards. Flowers may open spontaneously, tossing pollen up into the breezes, or when triggered by the visit of a large insect such as a bee, tossing pollen onto the insect’s body to be carried to another flower. Later on, the clump of red berries is equally showy. The leaves are typically evergreen, but sometimes turn red.
–rattlesnake plantain: an orchid that has nothing to do with snakes or plantains, whose evergreen leaves are sometimes mottled with dark blotches. It produces a spike of white flowers that may be bumblebee-pollinated but are reported to be more often visited by moths in our area. Like all orchids, it depends on mycorrhizal connections with other plants for seed germination and early seedling growth; this mutualism may also supplement the nutrition of adult plants. This orchid can spread vegetatively by rhizomes (underground stems), and we often see patches of it with many nonflowering stems.
–fern-leaf goldthread: the flowers are small and delicate, often male, but sometimes hermaphroditic (both male and female). An individual plant can be change sex expression from year to year; if it produces energy-expensive seeds in one year, it is likely to be male or non-flowering the next year. Later in the season, fruiting plants make an interesting whorl of seed capsules that fling out the seeds when jostled. The leaves are evergreen. Although it is found in dense forest, survival of young plants is better where the shade is less dense. The flowers are pollinated by small flies, such as dance flies.
–single delight or shy maiden: An evergreen member of the wintergreen family, its white flower faces downward until it is pollinated, when the flower raises its face upward, exposing the seed capsule with the tiny seeds to the breezes. The flower is buzz-pollinated by pollen-collecting bumblebees, which vibrate the anthers to release pollen onto the foraging bees.
–western coralroot: Spikes of pinkish flowers on pink stems usually appear in groups. There is no green pigment at all and no capacity for photosynthesis; these plants are indirectly parasitic on trees and shrubs, via mycorrhizal fungal connections, and also may be saprophytic (feeding on decayed organic matter). The flowers are visited by bees.
Those species all grow under dense coniferous canopy and are seldom seen outside the dark forest. It seems likely that they are able to inhabit the deep shade because they are evergreen and therefore capable of photosynthesis at any time of year if it’s warm enough, or dependent on other sources of energy. All can spread vegetatively to some degree, by means of rhizomes, and probably all of them form mycorrhizal associations with other plants. At least some of them, including rattlesnake plantain, seem to flower infrequently, suggesting that energy resources may be limited. Self-pollination may occur in some of them, with or without an insect visitation.
One other species is often considered to thrive in dense, moist forest in western North America: three-leaf foamflower. Unlike the previous species, foamflower is not evergreen; it reportedly does somewhat better under less dense canopies and is also seen along trails in more open areas. It would interesting to know how it manages in the deep forest. Other species are sometimes found in the forest, but usually in more open parts of the woods or on the edges: examples include starflower, calypso orchids, three-leaf goldthread, twinflower, two species of twisted-stalk, and violets.
Whether bona-fide deep-forest denizens or dwellers on the fringes, they all provide visual delights, sometimes olfactory treats (twinflower, maybe rattlesnake plantain), and interesting natural history.