Rare Woodland Plant

 This passage is adapted from “Rare Woodland Plant Uses

‘Cryptic Coloration’ to Hide from Predators.” ©2009 by

American Journal of Botany, Inc.

It is well known that some animal species use

camouflage to hide from predators. Individuals that

are able to blend in to their surroundings and avoid

being eaten are able to survive longer, reproduce, and

thus increase their fitness (pass along their genes to

the next generation) compared to those who stand

out more. This may seem like a good strategy, and

fairly common in the animal kingdom, but who ever

heard of a plant doing the same thing?

In plants, the use of coloration or pigmentation as

a vital component of acquiring food (e.g.,

photosynthesis) or as a means of attracting

pollinators (e.g., flowers) has been well studied.

However, variation in pigmentation as a means of

escaping predation has received little attention.

Matthew Klooster from Harvard University and

colleagues empirically investigated whether the dried

bracts (specialized leaves) on a rare woodland plant,

Monotropsis odorata, might serve a similar purpose

as the stripes on a tiger or the grey coloration of the

wings of the peppered moth: namely, to hide.

“Monotropsis odorata is a fascinating plant

species, as it relies exclusively upon mycorrhizal

fungus, that associates with its roots, for all of the

resources it needs to live,” notes Klooster. “Because

this plant no longer requires photosynthetic

pigmentation (i.e., green coloration) to produce its

own energy, it is free to adopt a broader range of

possibilities in coloration, much like fungi or

animals.”

Using a large population of Monotropsis odorata,

Klooster and colleagues experimentally removed the

dried bracts that cover the 3- to 5-cm tall stems and

flower buds of these woodland plants. The bracts are

a brown color that resembles the leaf litter from

which the reproductive stems emerge and cover the

pinkish-purple colored buds and deep purple stems.

When Klooster and colleagues measured the

reflectance pattern (the percentage of light reflected

at various wavelengths) of the different plant parts,

they indeed found that the bracts functioned as

camouflage, making the plant blend in with its

surroundings; the bract reflectance pattern closely

resembled that of the leaf litter, and both differed

from that of the reproductive stem and flowers

hidden underneath the bracts. Furthermore, they

experimentally demonstrated that this camouflage

actually worked to hide the plant from its predators

and increased its fitness. Individuals with intact

bracts suffered only a quarter of the herbivore

damage and produced a higher percentage of mature

fruits compared to those whose bracts were removed.

“It has long been shown that animals use cryptic

coloration (camouflage) as a defense mechanism to

visually match a component of their natural

environment, which facilitates predator avoidance,”

Klooster said. “We have now experimentally

demonstrated that plants have evolved a similar

strategy to avoid their herbivores.”

Drying its bracts early to hide its reproductive

parts is a good strategy when the stems are exposed

to predators for long periods of time: all the other

species in the subfamily Monotropoideae have

colorful fleshy bracts and are reproductively active

for only a quarter of the length of time. Somewhat

paradoxically, however, Monotropsis odorata actually

relies on animals for pollination and seed dispersal.

How does it accomplish this when it is disguised as

dead leaf material and is able to hide so well? The

authors hypothesize that the flowers emit highly

fragrant odors that serve to attract pollinators and

seed dispersal agents; indeed they observed bumble

bees finding and pollinating many reproductive

stems that were entirely hidden by the leaf litter itself.

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