Wildflower Wednesday: Pink Wintergreen

Gardens North is a fine place to find the seeds of many North American wildflowers and other unusual garden plants that are wildflowers in other parts of the World. They have a great on-line catalogue with thumbnails of flowers and information about their diversity of seeds that has helped me through many a long winter’s day. One thing that I especially like is that they point out problems one might have with their seeds. For example, for Pyrola asarifolia, which they stock, they note in their germination instructions: “There is no known method for germinating this species in an artificial setting.”

I’m not sure that I am up to that kind of challenge, but no worries, a P. asarifolia  seed or two figured out how to germinate in my yard all by itself. When I moved in I found a half-dozen leaves of Pink Wintergreen (also less euphoniously known as Bog or Liverleaf Wintergreen) peaking out from under the ground-hugging limbs of a giant white spruce, the trunk of which forms the southwest corner of a neighbour’s front yard, and the boughs of which formed a quite adequate barrier to block dogs from running across my yard. Other than mulching around the wintergreen and weeding out competing grass and dandelions, nothing much happened for several years until the neighbour decided to do some timber stand improvement and limbed the tree to 2m. Suddenly, dogs started crashing across the yard and previously invisible people strolling on the street seemed to always be staring in our front window whenever I had an inconvenient itch or trod through the living room in less than formal attire. A fence, a raised bed, numerous new plants, and a couple of years of labour later that corner of the yard is at least dog resistant. One beneficiary of the increased attention to that part of the yard has been the wintergreen. What was once a half dozen marginal-looking leaves is now a spreading groundcover. Even better, attractive spikes of pink flowers began appearing last year and have just started blooming again this year.

It is sometimes said that the highest diversity of plants in temperate forests is the stratum of the herbs and small shrubs near the forest floor (e.g. a pleasant stroll through the understory in the Saskatchewan River Valley see The Garden Ms S). I suppose that it true – the understory of tropical rainforest tends to be boring – all of the action is in the sun-drenched canopies where trees, epiphytes, and lianas express their diversity 50 or more metres above ground. Since light is at very low levels on the forest floor, understory plants often grow very slowly and try to keep their leaves as long as possible, even in very cold climates. Being evergreen is a way to conserve previous investment in growth and take advantage of any light that happens to come along when temperatures are warm enough for photosynthesis.

Another way for forest floor plants to persist in low light levels has recently become a fervid topic of research interest – myco-heterotrophy. The associations between certain fungi that collect mineral nutrients and the roots of plants that exchange excess carbohydrates for these nutrients (mycorrhizal associations) has been known for a fair amount of time. You can even buy ‘mike’ preparations at the nursery to inoculate your perennial transplants. Some plants, however, depend on fungi for more than just minerals – they steal carbon (sourced directly from the air via the sun and photosynthesis in your typical green plant) from fungi. The extend of dependence on fungal carbon varies - from only during germination (possibly this is why Pink Wintergreen is so difficult to germinate - they need a certain fungus or two), to others such as Pyrola aphylla or certain leafless orchids (e.g. Corallorhiza maculata) that are completely dependent on mycorrhizal fungi – and their vascular plant hosts – for all of their carbon and nitrogen.

 Like most of its relatives, the Pink Wintergreen has unusual stamens that release pollen only from a pore at the tip (tomatoes and their relatives also have this type of stamen). Only certain bees are able to collect pollen from these flowers through a technique called buzz pollination. Essentially, a bee grabs hold of a stamen and shakes the pollen out by vibrating its wings and body. Most of the northern European species of wintergreens (including Pyrola minor, rotundifolia, chlorantha) studied by Knutsen & Olesen (1993 American Journal of Botany 80: 900-913) did not produce nectar and were mainly buzz-pollinated by bumblebees (Bombus spp.). The pistil is located far away from the stamens, so one would assume that outcrossing is preferred by Pink Wintergreen. We have lots of bumblebbees in the Home Bug Garden, and also leaf cutting bees (Megachile spp.) that are good buzz-pollinators, but instead of spending my days watching the pyrola to see what comes to pollinate, I trudge off to work. No accounting for taste.