Monday, April 26, 2021

Bloodroot's Bet

This herbaceous perennial is among the first to bloom on the deciduous forest floor. It's also among the hardiest.

Bloodroot, Sanguinaria canadensis, in early April 2021.

Every year, bloodroot throws the dice. It blooms surprisingly early, risking the return of winter weather to grow and flower when light intensity is highest on the deciduous forest floor. Its way of surviving in shade is to mostly avoid it, and thanks to several adaptations to cope with the uncertain conditions of early spring, it has succeeded.

Sometime in late March or early April, single basal leaves spear through the leaf litter, wrapped around and protecting flower stalks bearing one, delicate bud. On dry, sunny days, the flowers open like bowls, each a brilliant display of eight or more petals around a mass of orange-yellow stamens and a central pistil.

Little else is blooming at the time, so bloodroot doesn’t have much competition for the few pollinators that are active in early spring. Although bloodroot has no nectar, insects nevertheless circle over the flowers in search of a sugary sip.  A few will land inside, and over the course of a few days, they will find that Bloodroot’s offerings change.

When a flower first opens, only the stigma is mature. The anthers need another day or two before they’re ready to release any significant amount of pollen. Although visiting insects won’t find much pollen to gather from a young flower, they can deliver what they collected from an older one. In rapid succession, the stigma receives the pollen, the eggs are fertilized, and seeds begin to develop. Such cross-pollination has the advantage of mixing genes from different plants, creating new combinations that might improve offspring survival.

Self-pollination isn’t likely to occur at this stage, in part because the anthers aren’t mature but also because the stamens initially bend away from the pistil. By day three in a flower’s life, however, the anthers are fully developed and the stamens change their position. Instead of bending away from the pistil, they bend toward it, increasing the odds that the flower will fertilize itself.

Left: In recently-opened flowers, the stamens and immature anthers bend away from the pistil.
Right: In an older flower (three days or so), the stamens bend toward and even arch over the pistil.

In a sense, this is bloodroot’s life insurance policy. If cross-pollination doesn’t happen – say in a stretch of cold, rainy or snowy weather that limits pollinator activity – self-pollination is a fallback. The resulting seeds will produce offspring much like the parent, but at least there will be seeds, tiny propagules that can be disseminated to expand the population.

Whatever ate these Bloodroot leaves might not have
enjoyed them for long. Bloodroot sap contains several
alkaloids, bitter molecules that can be harmful.

Of course, insects aren’t the only animals looking for food in early spring. Hungry herbivores are also on the prowl, and bloodroot provides some tempting, tender shoots. One chomp and bloodroot could lose its annual opportunity to grow and reproduce. The “blood” of bloodroot tends to discourage that activity, however. It contains several alkaloids, molecules that are distasteful if not harmful to animals that eat them. Alkaloids are most concentrated in the roots, but they are found in all parts of the plant, including the leaves and petioles. A mouthful of the bitter greens could be enough to put an herbivore off bloodroot for a long time.

It’s a gamble to grow early, but bloodroot has adapted to the risk. The plant's fragile appearance belies a durability born of countless generations on the forest floor. Through genetic trial and error, the dice came to be loaded in its favor.     

References

Hayden, W.J. (2005). Bloodroot pollination: Bet-hedging in uncertain times. Bulletin of the Virginia Native Plant Society 24(1): 5+

Matsuura, H., & Fett-Neto, A. (2015). Plant Alkaloids: Main Features, Toxicity, and Mechanisms of Action.

Schemske, D.W., Willlson, M.F., Melampy, M.N. et al. (1978). Flowering ecology of some spring woodland herbs. Ecology 59 (2): 351-366.


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