Parasitism in Plants

Orobanche uniflora - One-flowered cancer root

When I came across this oddity growing on the woodland floor of Halibut Point it set off an investigative trail into the subject of parasitism. All parts of the Orobanche uniflora were white or essentially colorless which meant that it lacked chlorophyll and was incapable of making its own food. Therefore it had to be living at the expense of others.

I considered the negative associations of the word parasitism in art and science. I reflected on my own whiteness, lack of chlorophyll, and inability to make my own food. A parasite to plants? The paths of art and science blinked with caution lights. I didn't want to be associated with something small, creepy and invasive that takes without giving in return.

Research brought me to a distinction between parasites, which are typically much smaller than their hosts, do not necessarily kill them, and often live in or on their hosts for an extended period; and predators, which kill and devour right away. Honest predation seems the cleaner, if more lethal, individual existence, when considered one meal at a time.

Our prolific species requires billions of meals a day from our host organism Earth, living at the expense of others. I consider adjustments to my notions of parasitism. Possibly from the lighter side entomologist E. O. Wilson characterizes parasites as "predators that eat prey in units less than one."

Orobanche uniflora, the One-flowered cancer root, has no use for leaves because its roots invade other plant species for water and nutrition. It does have pretty flowers that produce seeds for self-perpetuation, which it has to be good at because it's an annual. Being categorized as a parasitic plant means it leads a one-sided robber's life. I wonder if we know the whole story about Orobanche uniflora's ecological relationships. Endurance in my experience isn't typically designed around one-sided behavior.

Monotropa uniflora, - Indian pipe, corpse plant

Indian pipe is a similar-looking plant with a more charming name and mode of existence. Until recently I thought it a respectable saprophyte, deriving its energy from dead organic matter. Modern investigation reveals that it has short stubby roots that harbor fungi. The fungi extend their organic threads through rotting humus to connect up to the roots of conifers. Termed mycorrhizal they maintain a mutualistic relationship with the tree, helping it absorb nutrients from the soil. The conifer in turn manufactures sugar which it shares with the fungi. Indian pipe may be parasitic to what we know of this process, but maybe not. At any rate it attaches to the fungus and not directly to our friend the tree.

 

Comandra umbellata - bastard-toadflax, a hemiparasite

Many shades and degrees of 'parasitism' have developed in the diversified quest for life. One of Halibut Point's plants Comandra umbellata is classified a "hemiparasite'  because it has both green leaves that use photosynthesis and also attaches specialized roots (haustoria) to the roots of a host-plant to derive some of its nutrients. Comandra's energy balance sheet is complicated by the fact that it produces edible fruits for consumption by animal species.
 

Agalinis purpurea - Purple agalinis

Another Halibut Point native Purple agalinis disguises its hemiparasitic operations by appearing to be pretty and innocent above ground. Meanwhile its haustoria are busy transferring sugars and proteins from the subterranean tissues of host plants to its own benefit.

Cuscuta epithymum - Clover dodder
Photo from the GoBotany website

If you prefer a more horrifying version of parasitism look for dodder, which lacks the respectability of roots and leaves and wraps its vampire strands around defenseless plants.

If the 'host' contains food it senses to be beneficial  the dodder inserts haustoria into its vascular system. The original, now unnecessary root of the dodder in the soil then dies. The dodder can drape itself over multiple plants.

Life's myriad processes tumble along. Is it a neutral game? All I know for sure is the importance my own defense system, and the satisfaction of my next meal.