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Bristlegrass

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By Jake Landers

Published March 2013

Jake Landers Southwestern bristlegrass grows in August in shadow of building in downtown Menard, Texas, on ancient floodplain soils. We have several native perennial Bristlegrasses that are important in our pastures.  We also have a bunch of annuals we received from the Old World.  The natives are rancher friendly, but the aliens are aggravating to farmers as weeds in crops and fields, and one of them is especially aggravating to me in my garden.

Southwestern bristlegrass in our deep soils is the largest of the natives with Plains bristlegrass smaller and more widespread in our rangeland.  Grisebach bristlegrass is in between and sometimes overlaps in appearance with Southwestern bristlegrass to make identification untrustworthy.   Knotroot bristlegrass is similar to Plains with knotty roots. 

Most of the seed heads of the Bristlegrasses look like overgrown toothbrushes, but Reverchon bristlegrass has lost all of its bristles except for one or two per seed (spikelet) due to genetic changes.

Reverchon bristlegrass retains one tiny bristle at each seed, hardly visible even at this high magnification.  Photo by Ricky Linex. The loss of bristles is an evolutionary process that doesn’t answer the question, “Why?”  A trend that reinforces itself is called “positive feedback.”  How the loss of bristles, or for that matter, the gain of bristles in other species, gives an advantage to the next generation as a driving force in evolution is unknown.  Little things, however, are helpful in our identification and classification of grasses.

You don’t need to worry about the scientific names unless you are serious about the study of grasses.  They are Setaria scheelei, Southwestern; S. grisebachii, Grisebach; S. leucopila, Plains; S. parviflora, Knotroot; S. reverchonii, Reverchon; and S . ramiseta (No common name).  One alien from the Old World is S. adhaerens, Hooked bristlegrass.

The seeds of Bristlegrasses are about the same size of the grain we call Millet, which is one of the annual grasses from the Old World brought into cultivation by our ancestors.  Most of the other annual Bristlegrasses evolved on their own as weeds among the cereal crops of early times, and were inadvertently brought here mixed with crop or bird seeds.  In crops they can be very damaging weeds.  Germinating and growing by the bird feeder, they can be an interesting and often surprising addition to your backyard flora. 

Hooked bristlegrass is a bothersome weed in my garden and flower beds. It got here somehow from the Old World.  When it’s mature the seed heads hook onto anything, and like Velcro, will not turn loose easily.  Socks, dog fur or double-knit pants can be plastered with bristles and seeds that don’t come out easily in the washing machine.

Hooked bristlegrass becomes all tangled up because of the tiny hooks on the bristles, helpful in moving the seeds to a new site to become established. A single bristle—called an awn if it’s longer, or seta if shorter—is shorter than a cat’s whisker and more complicated in construction.  It grows, like all plant parts, one cell at a time from the genetic instructions provided in the plant’s DNA, combining molecules of cellulose for structure and proteins for glue in a bath of watery sap that is hard to envision in a dry-looking grass. If the DNA says so, hooks are made at regular intervals along the length of the awn or it stays smooth.  Through the ages of its existence, each Bristlegrass has survived and prospered in different habitats with its own characteristics, with hooked or smooth awns.  The bristles, as to size and number, are most useful in the identification of species.

For doves, quail, and other seed eating birds, the Bristlegrasses are of great importance.  As a grazing resource the Bristlegrasses are in the category of fair.

Our natives persist as perennials on rangeland, and are seldom in abundance, but the annuals from the Old World can dominate cultivated ground with much vigor.  All grow during the warm season when moisture is available.


Reading The Landscape

Perhaps this is a dreary winter scene in central Texas for some, but to an owner interested in ranching for a living, it may better be described as depressing.  Why?

Perhaps this is a dreary winter scene in central Texas for some, but to an owner interested in ranching for a living, it may better be described as depressing.  Why?     —JL

See below for Jake's answer

































Reading the Landscape: Answer

Jake’s comments: Dense Mesquite with some Pricklypear cactus visible in the left pasture would indicate severely reduced grazing potential for livestock and lack of desirable browse plants for deer.  Though this was historically open country, Mesquite trees have come in since the 1920s.  Fire lines have been cleared between pastures and along the highway suggesting the rancher will use prescribed burning in the future to improve forage production.         —JL


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