Yesterday I took a trip to Muddy Brook Wetland Preserve out on Van Sicklen Rd with Boots + Sophia. It’s a pretty wet area – as the name would imply – with different levels of “wetness” and so lots of species of dogwoods, willows, and viburnums. With all the variety it’s a great place to bone up on ID skills. Not a bad soundtrack this time of year either with all the warblers (e.g. chestnut-sided warblers, common yellowthroats).
One thing that caught my eye was the striking color of the red maple seeds that had fallen to the forest floor (each clump of unripe seeds had either been torn off or nipped off by squirrels, not shed actively by the plant to be dispersed by the wind). Red color in plants is caused by the class of pigments calledÂ anthocyanins. Their primary function is to act like a sunscreen, protecting plant tissues from harmful radiation (check out the contrast between the color of the top vs bottom of your raspberry canes). In the fall these colors are produced to protect deciduous leaves while theyÂ deconstruct themselves toÂ reabsorb nutrients/energy. In the spring, the protective pigments likely protect young leaves that don’t yet have a cuticle (a waxy protective layer).
I didn’t find specific research confirming/rejecting another hypothesis: that a plant could use the bright coloration to ward off would-be herbivores from eating them. There are many examples in the animal kingdom of aposematic coloration to deter predators. TheirÂ bright, flashy colors warn predators of their toxicity (think skunks, dart frogs, monarch butterflies, lady beetles). To test this hypothesis, we’d need to know if these plants had higher concentrations of toxins than their verdant counterparts. As I’m writing this though I’m realizing that most of these plants lose their red/purplish hues as they mature. It’s not like potential predators dissipate as spring turns to summer – just the opposite is true. Maybe the leaves have mechanical defenses (again, that waxy cuticle and tougher fibrous dermal cells). Or maybe it indicates that the color does indeed only protect the plant from harmful UV radiation. I can’t think of any plants that retain their purplish colors into maturity. Why spend energy making warning colors and then getting rid of them?
Another reason why my hypothesis is probably not totally true as that the opposite is true of these colors on certain plant tissues. Fruits often start out green and only turn a bright showy color to advertise to herbivores that the fruits are ripe and can be eaten. This gives the plant enough time to develop seeds with adequate seed coats to protect against the acidic digestive tracts of mammals and birds. Red maple goes from red to green but it’s not advertising to animals to eat it as it relies on the wind for dispersal.