Tricky Tick Trefoils

(The pod sticks like a tick. Trefoil refers to the trifoliate leaves)

Desmodium tortuosum and so many more species

Fabaceae

This weekend’s botanical joy has been a study for plant physiology class of the leaf movements by Desmodium leaves to light changes and biological rhythms. Boring to most folks no doubt, but one of the tricky treats we all can see in this back yard marvel. The leaf bases have muscle power, true of most legumes and big-time in Desmodium. The leaf-muscles are called pulvini (pull-VINE-ee), and wiggle-waggle the leaf blades up and down in response to the plant’s wants and needs.

Flowers and segmented pods (John Bradford)

Anybody with socks or pant cuffs knows Desmodium for its laundry fun. The segmented flat pods cling to fur and fabric with hooked hairs like Velcro. Although a hiker’s nuisance, it’s quite an evolutionary trick to take a flat “peapod,” segment it into break-apart pieces like a Kit-Kat bar, and give them stick-o-rific hairs. I find that as amazing and awesome and phenomenal as any ol’ orchid flower, but sadly there are no Desmodium Societies to join.

Possibly the beggar-lice helped make Desmodium such a successful genus, with some 300 species around the world, with two dozen in Florida a mix of native, introduced, and of ambiguous nativity. Anything that clingy gets around, and how much of that travel over thousands of years is “natural” is impossible to say. Weeds is weeds.

Just to narrow the field, let’s zoom in on a big one, “Florida” Tick Trefoil, Desmodium tortuosum. The book in front of me deems it not native, but other authorities place its “natural” origins as close as Cuba, and who’s to say those pods don’t sometimes cover the 90 miles without human help! So let’s not be overly dogmatic. In any case, humans sure have moved it around the southern U.S. quite a bit on purpose.

Here’s a case of why flip-flopping with Mother Nature is not always wise. A couple generations ago the species was “good”—even planted. It smothered weeds. It fixed nitrogen. It was a green manure, a cover crop, living mulch. It succeeded…opps, a little too well.

Modern Dixiemodium tortuosum tortures agriculture. (The “tortuosum” refers to the twisted pods.) It is arguably the #1 peanut weed in Georgia, prompting lots of herbicide spraying. I wonder if any gets into the Skippy. Desmo-tort pesters peanuts something awful. I just read that a single specimen about 2 feet from a peanut plant can diminish the yield by almost 20%, and just 8 desmodiums per approx. sq. yard can cut peanut production by over a third. That’s a serious weed, and it gets in the way of adding fungicides. Farmers are lucky that Dixie Tick Trefoil is one of the few annual Desmodiums, rising up during late season growth. Certain herbicides can be timed to pass over the early-growing peanuts and to suppress the later-maturing Desmodium.

Let’s end on a more colorful note. A curious aspect about Desmodiums is mixed flower color, even on single individuals, the combo usually being lilac flowers mixed with blue-ish blossoms (as well sometimes as white). This link shows a mix on the same inflorescence TRIP HERE and look closely.

Mixed colors are not rare in plant species, and are generally interpreted as a signal to pollinators conveying the reproductive status of the flower, let’s say nectar availability. It would be reasonable to regard the changes as mere floral age, but some Desmodium species take it a step further. The flowers have a tippy landing platform with the anthers and stigmas concealed until a bee lands, fairly standard for many legumes. In Desmodiums, the penetrating bee “trips” the flower on a one-time basis like a rat trap. The tripped flower pulls the trigger on the color change: “attention pollinators: this flower is taken care of, so go find another.”

Bluestem Grasses

11 Oct

Andropogon (and Schizachyrium)

Poaceae

Today’s sunny fieldtrip took John and George through the north end of Seabranch State Park near Hobe Sound, Florida, the present epicenter of our green interests. Today’s word to describe the glory of nature: Bluestem Grasses!

All Bluestem Grass photos today by John Bradford.

These are those large puffy-topped grasses, sometimes over 6 feet tall so pretty in October. Always reluctant to pick favorites, apply tickle-torture and I may confess preference for those gorgeous wands of puff. It isn’t just the silvery tops dancing in the breeze, but also the array of foliar colors. So autumnal, a celebration of sunbeams and flickering memories, such as fond recollections of childhood strip mines.

I grew up in West Virginia immediately across the Ohio River from bigtime earth-rape. Bluestems restore a tentative wisp of beauty to the toxic post-mining landscape. (“Restoration,” yea sure. Let’s go see the phosphate mines here in Florida.) CLICK to see a Bluestem (“Broomsedge”) consoling an old mine crater in Illinois.

Bluestems make all the difference along roadsides, in old abandoned farm fields, along railroad tracks, and on rocky hilltops across much of North America and worldwide. By the way, grouse like them. Here is a Bluestem enhancing John’s path of life.

Several species coexist locally. If you are nutty enough to try to sort them out, try our grassy web site. Distinguishing these species can be extra-exasperating because: 1. The common species can be bewilderingly variable. 2. Different nearby regions house different species assortments. 3. Some hybridize. 4. They do not stick to their textbook habitats or to field-guide dimensions. So for today, they’re just all “Bluestems.”

Andropogons usually have two bunny-ears.

As hinted a moment ago, they tolerate the world’s worst soils: graded roadsides, rocky hilltops, hellish railroad tracks, and scrub. These rugged grasses have a few tricks, some of them studied in only one or few species.

Trick #1. Some Bluestems have symbiotic root fungi (mycorrhizae) procuring phosphorus from shamefully nutrient-poor soils.

Trick #2. Bluestems suppress potentially competing vegetation. It is not mere competition. Recent research shows some to diminish the “normal” nitrogen-fixing (fertilizer-providing) bacterial associates of non-grass species.

Grasses are turning out increasingly to have their own symbiotic arrangements with unconventional nitrogen-fixing bacteria. Although data are sparse and preliminary, Bluestems sometimes have such unconventional nitrogen-fixers. So could they sabotage the other guy’s nitrogen relations while enhancing their own, making the Bluestems kings of the starved soils? Can they form a nitrogen monopoly?

Even weirder, one species preferentially takes up its soil nitrogen as ammonia, as opposed to slurping in nitrate, the other form in which plants take up nitrogen. The selfish Bluestem is able to diminish soil nitrate to the detriment of potential competitors, while it somehow enhances soil ammonia for its personal private consumption.

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Posted by George Rogers on October 11, 2014 in Bluestem Grass

Tags: Andropogon, Bushy Bluestem

Bluestem Grasses – Andropogons

29 Oct

Bluestem Grass

Andropogon, several species

Poaceae

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.

Splitbeard Bluestem with its split beard (don’t recall who took the pic)

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.

Andropogon ternarius spikelet cluster. Center-left is large fertilie spikelet with long awn. Smaller sterile spikelet “dagger” is vertical just center-right. Another awn is visible tilted to the right.

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.