Monday, June 27, 2022

Plant Profile: Bunchberry

 Cornus canadensis L.

Bunchberry, Cornus canadensis, flowering in northern Minnesota in mid-June 2022.












Also called Canada dogwood or creeping dogwood, bunchberry is a patch-forming, herbaceous plant of cool, moist forests. Although it’s related to red osier dogwood (C. sericea), gray dogwood (C. racemosa) and other shrubs, this plant has no aboveground woody growth. Mature plants are just 3-6 inches tall, their short stems tipped by four to six, arc-veined leaves that are so closely spaced they appear whorled.

In late spring or early summer, mature plants produce a cluster of 12-40 small flowers surrounded by four white bracts. The petals of the flowers are just 1-2 millimeters long (1) and fused along their edges until they open.

The stamens of the flowers grow quickly, faster than the petals. As they mature, their anthers, the pollen-producing tips of the stamens, are trapped inside the closed flowers, but their lengthening filaments bend outward between the petals. Eventually, a trigger – a visiting bumblebee, for example, or just maturity – causes the flowers to open explosively. As the petals flip back, the stamens spring outward, and pollen is catapulted into the air (2,3). The grains can be lofted as high as 2.5 centimeters (25 millimeters) above the flower, ten times the height of the flower itself (3).


A single bunchberry flower opens explosively -- in about half a millisecond (3). When the petals flip back, stamens are released and catapult their pollen. Illustration based on photographs in Whitaker, et al. (2). 











[Watch a video of an exploding flower here.]

If they’re launched at high enough speed, some of the pollen may catch in the hairs of flying insects, which then carry it to other plants. Other pollen rides the wind. Unlike plants that are pollinated only by insects, bunchberry pollen grains are smooth instead of sticky, the better to be carried in a breeze (2).

A dual system of pollination is an advantage for bunchberry. These low-growing plants are self-incompatible, so they need pollen from other plants to form seeds. If insect pollination isn’t successful, wind pollination might be, but for the latter to work, pollen must be launched high enough to be wafted over a patch of the plants.

If either method of pollination succeeds, the plants will produce bunches of red drupes, fruits with single, stony seeds. The fruits look like berries, inspiring the name bunchberry.

Where to find bunchberry

Bunchberry typically grows in cool, moist broadleaf, coniferous or mixed forests. In North America, its range is primarily the northern tier of states, all of Canada, and Greenland (4). This circumboreal plant is also found at northern latitudes in Asia.

More information

For photos and more information about bunchberry, see the Minnesota Wildflowers page for this species.

References

(1) Flora of North America, efloras.org. Accessed online on June 27, 2022. Formal citation: eFloras (2008). Published on the Internet http://www.efloras.org [accessed 27 June 2022]. Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.

(2) Whitaker, D., Webster, L., and Edwards, J. (2007). The biomechanics of Cornus canadensis stamens are ideal for catapulting pollen vertically. Functional Ecology 21. 219-225. DOI:10.1111/j.1365-2435.2007.01249.x

(3) Edwards, J., Whitaker, D., Klionsky, S. et al. 2005. A record-breaking pollen catapult. Nature 435, 164 (2005). https://doi.org/10.1038/435164a

(4) USDA, NRCS. 2022. The PLANTS Database (http://plants.usda.gov, 06/27/2022). National Plant Data Team, Greensboro, NC USA.


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