Andropogon, several species
Hurricane Sandy and Hurricane Work Obligations thwarted the usual Friday trip this week. A little alter in time, this morning dawned cold and brightly sunny, and I visited the Sweetbay Natural Area near the Palm Beach North County Airport. One of John’s and my favorite wet sites with a civilized paved sidewalk. The cold was compensated by the striking beauty of the horizontal sunbeams lighting up the silvery beards on the various Bluestem (Andropogon and Schizachyrium) grasses. Those fireworks alone justify an early start.
It is not my purpose now to be schoolin’ ya about how to distinguish the Andropogon species. John and I tried that, and the results are a click away at floridagrasses.org.
Some readers might agree that locally the Bluestem Grasses can be tough to differentiate. Whenever you see reference to a “species complex,” watch out for a puzzling network of funny business. Most of our nearby species belong to the “Andropogon virginicus complex,” which seems to be diploid, comparatively free of apparent hybridization, and yet often with subtle visible differences between species.
One of the prettiest and most distinctive species is the Splitbeard Bluestem, Andropogon ternarius, which is a tetraploid (has 4 sets of chromosomes) and has a particularly delicate appearance: tall and slender with big long silvery-white bunny ears (spikelet clusters) displayed on wirelike wands. It looks like a work of art, and I always enjoy encountering this exquisite bit of creation. Gardeners agree. I recently saw this species for sale at approximately $40 per cell tray. A seedy variant developed in Florida chiefly for habitat restoration is called “Ft. Cooper.”
The plant world is full of fluffy-puffy feathery wind-dispersal units, but Andropogons are the ZZTops of the flora. In fact the name Andropogon means dude with a beard.
You could scarcely design a species more appropriate to wind-dispersal. The bunny ears bust apart at the slightest whisper, separating into parachute-bearing “seeds” (spikelet clusters) to blow hither and thither. The microscope view shows what they bust apart into. The feathery parachute hairs in the photo are of obvious function. The two long threads (awns) visible in the picture are less obviously useful. The awns probably catch the wind or bump against adjacent plants and help the bunny ears bust apart. Also interesting are the two small vertical “daggers” you see flanking the main spikelet. Those are sterile (seedless) spikelets. Who knows—maybe they’ve lost their function but the genes that make them have not quit altogether, sort of like the human canine teeth.
The natural distribution of Andropogon ternarius is roughly the southeastern 1/3 of the US from Florida to New Jersey, Indiana, and Texas. At least that was where it was is was yesterday. Sandy may redistribute some bunny ears today.