Don’t Nap on the Carnivorous Grass

30 Dec

Switch Grass
Panicum virgatum

What could be more boring than an article on grass?  Well, hey now, as a grass lover, I take offense at that narrow attitude!  Switch Grass is in fact an interesting grass.  Gardeners think so, with their fancy colorful cultivars, such as ‘Prairie Fire’ and ‘Ruby Ribbons’.  A more pragmatic energy-hungry world likes Switch Grass too: as a potential cellulosic biofuel, if anyone manages to start turning cellulose commercially into ethanol. According to Scientific American the yield from Switch Grass is over five times the energy used to produce it, compared with a wimpy 1:1 with corn.

Switch Grass (by JB)

Switch Grass (by JB)

Cellulosic ethanol may power the Ta-Ta in your future, but even more amazing, who ever heard of flesh-eating grass?  In a world of some 12,000 grass species, a local native may be the first documented mowable carnivore.  No, I have not effectively checked for other meat-eating grasses, but in any case, it turns out yet again that underground Florida is a strange social network.

Switch Grass inflorescence (by JB)

Switch Grass inflorescence (by JB)

That plant roots form symbiotic (mycorrhizal) contracts with fungi has long been known.  Mycorrhizal fungi help decay soil organic matter and shunt the results directly into the host plant.  Mycorrhizae are deemed especially important for phosphorus acquisition, as this nutrient does not “flow” into the roots in water as readily as nitrogen does.

To continue with the already-known, that fungi can attack, kill, and digest soil insects won’t stop the presses either, although commercial insecticidal applications sure are something.

But now dare to dream, and put those two hackneyed fungal phenomena together into a new innovation: insectivorous mycorrhizal fungi.  Switch Grass has em’.  The fungus Metarhizium robertsii has been shown to infect and murder soil insects, and to transfer the bug nitrogen to Switch Grass (and to beans).

The species is perhaps at heart a tallgrass prairie grass, with an enormous range sprawling from Canada to Costa Rica (and probably by introduction, to Argentina).  Here is our area, it is not rare, but not dominant, a visual treat mixed in with other grasses and sedges.

Out botanizing, it is easy to recognize Switch Grass.  The plants are often large and attractive, let’s say 3′-5′ tall with an open, airy, vaguely pyramidal inflorescence.  It looks somewhat like the non-native Guinea Grass (Panicum maximum), but differs in a way that is easy to see:  rub the spikelets briskly between your corn husker hands.  In Guinea Grass there is an inner white nugget (technically a hard lemma) white, bony, and wrinkled. Nothing like that in Switch Grass.

Getting back to biofuel, that might be more valuable.  But then again, maybe biotechnology can find a way to transfer bug-eatin’ ability to St. Augustine Grass so a few million acres of lawn in Florida can feed on its own grubs instead of megatons of lake-choking fertilizers.

Dog captured by carnivorous grass.

Dog eats grass is not news.   Grass eats dog, now that’s news.

Note: For readers interested in deeper reading:

1 Comment

Posted by on December 30, 2012 in Switch Grass


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One response to “Don’t Nap on the Carnivorous Grass

  1. George Rogers

    March 20, 2016 at 9:16 am

    thank you!


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