Sunday, February 06, 2011

Sandbur

What’s happening: We won’t know until spring how much has been killed by these bitter temperatures and dry ground; Russian olives, juniper and pyracantha berries persist.

What’s still green: A thin layer of snow covers most things; evergreens, yuccas, some grasses show.

What’s grey, blue-grey or grey-green: Piñon, four-winged salt bush and winterfat leaves.

What’s red/turning red: Cholla leaves; rose stems, although they’ve been covered with icicles since Thursday.

What’s yellow/turning yellow: Globe and weeping willow branches.

What’s blooming inside: When we lost our heat Thursday morning, I brought everything into the house where temperatures fall to the 40's, rather than the 20's.

Animal sightings: Rabbit tracks in snow when I left for work mid-morning Thursday.

Weather: The temperature fell to -12 Thursday morning, the lowest I ever remember, with only the slightest snow cover; last snow 2/5/11; 9:53 hours of daylight today.

Weekly update: This is the time of year when the most noxious weeds find ways to make human intruders plant their seeds. When I came in Wednesday morning from clearing snow off a thermometer that read 4 degrees, I had a sandbur in my heavy wool sock. It must have been hiding in my rubbers since I last wore them in December.

While I won’t believe it was lurking in the snow, I can believe the sandbur represents one of nature’s most hostile responses to changing environmental conditions.

The Cenchrus genus of grass probably emerged in tropical east Africa. Amelia Chemisquy’s team believes one of its ancestors was the parent of either Pennisetum ramosum, found today in tropical Africa, or Pennisetum orientale, which ranges from northern Africa through the Arabian peninsula into the Caucasus and Himalayas. The other possible parent was the progenitor of Pennisetum setaceum, which grows from tropical Africa north to the Mediterranean littoral that spreads from the Maghreb to the Levant.

Cenchrus longispinus probably developed in North America where it ranged from the Continental Divide to the Appalachians in 1971. Early in the twentieth century, Elmer Wooten and Paul Standley called it one of "the most pernicious weeds" in New Mexico, common in sandy soil at lower elevations throughout the state. Tewa speakers called it Ta nwæ’ig or thorny grass; Spanish speakers called it roseta.

This particular species has become an annual, no longer dependent on warm temperatures for survival. While the seeds may only last about three years, their germination rates are high. J. D. Twentyman found over 96% of those that managed to be buried, germinated within 2 years.

More important, he discovered the burs hold two types of seeds. The ones in the upper spikelet germinate within a year. The lower ones go dormant, and emerge more slowly. They’re programmed to not germinate when exposed to light or unfavorable high or low temperatures.

Beginning in May, the seedlings, which resemble barnyard grass, emerge directly from the bur. Various experts advise people they can confirm their identity by poking around the roots for the burs. This seems silly for two reasons: if they are sandburs, you hurt your finger; if they’re not, you harm a grass you might like to encourage in its place.

I’ve learned the leaves emerge in a V on opposite sides of a center, much like iris leaves. At that stage, the plant is flat to the touch. The more desirable grasses tend to be rounded. Still when you pull them, the underlying bur doesn't come out, but stays in the soil with that slow germinating seed.

Soon after, the leaves start to grow flat in a circle and resemble crabgrass. In July, zig-zagging stalks emerge from the center with bright green flower receptacles that already bear sharp spines. Inside are two minute flowers: the upper one is fertile with two stigmas, the other sterile or male. Flowers continue to appear as the stalk elongates, so the lower burs already hold viable seed while the top is still blooming.

Removing the plants at this time is much trickier than in June. I reach under the leaves and pull the fibrous roots from the soil, then try to carry the flat, round disk of a plant so no part can touch me. When I drop it in a plastic trash bag, I tell myself to remember it’s there so I won’t put something in later and reach down to compact the contents.

The prickles on the oval burs are formed from fused aborted branches on the flowering head. The lower spines are shorter that those above, and point downward. They all attach like velcro.

The only way to remove them is to use your nails and get beneath them so as few spines as possible find your flesh. It’s surprising how quickly you learn to remember the hidden contents of a trash bag.

As the plant completes its annual cycle, the burs harden and fall from the stems. With a killing frost, both the burs and remaining leaves fade to a whitened sand that emphasizes the ridges in the leaves and the sharp spines. By the following spring, the burs are dirty brown. The only ways they can be removed from the surface then is with a trowel or, less happily, a sleeve or pant leg.

During the fall and winter, the burs prevent most animals from eating the one to three seeds within. However, mice are more cunning. Around Pinckney, Michigan, prairie deer mice eat the seeds, while sandbur seeds are collected by plains pocket mice in Minnesota and hispid pocket mice in Oklahoma.

Longspined sandburs can pioneer seemingly barren soil and attach themselves to the animals who may be responsible for the devastation. In the past, I suspect they used the large mammals, then the buffalo to migrate and reclaim disturbed areas. More recently, they have followed sheep and men. They particularly like to colonize abandoned farm lands.

The seeds also punish those sloppy in their harvesting techniques. Wooten and Standley said the burs were particularly common then in alfalfa fields, suggesting contaminated seed. They migrate to Australia in corn exported from this country, then make handling wool dangerous.

Sandburs don’t much like competition - they need the wind to bury and fertilize them. Eventually they will die out where other plants are allowed to take over. However, I suspect even then the impotent burs will persist to attack anyone who wants to redisturb the ground, a knightly protector even in death.

Notes:Australia. Department of Agriculture, Fisheries and Forestry. "Weed Risk Analysis of a Proposed Importation of Bulk Maize (Zea mays) from the USA," March 1999.

Blair, L. F. "Faunal Relationships and Geographic Distribution of Mammals in Oklahoma,"
The American Midland Naturalist 22:85-133:1939.

Chemisquy, M. Amelia, Liliana M. Giussani, María A. Scataglini, Elizabeth A. Kellogg and Osvaldo Morrone. "Phylogenetic Studies Favour the Unification of Pennisetum, Cenchrus and Odontelytrum (Poaceae): A Combined Nuclear, Plastid and Morphological Analysis, and Nomenclatural Combinations in Cenchrus," Annals of Botany 106: 107-130:2010.

Curtin, Leonora Scott Muse. Healing Herbs of the Upper Rio Grande, 1947, republished 1997, with revisions by Michael Moore.

Hibbard, E. A. and J. R, Beer. "The Plains Pocket Mouse in Minnesota," Flicker 23:89-94:1960.

Howard, Walter E. and Francis C. Evans. "Seeds Stored by Prairie Deer Mice," Journal of Mammalogy 42:260-263:1961.

Iowa State University. Department of Ecology, Evolution, and Organismal Biology. "Sandbur (Longspine Sandbur)," Grasses of Iowa website.

Robbins, William Wilfred, John Peabody Harrington, and Barbara Friere-Marreco. Ethnobotany of the Tewa Indians, 1916.

Twentyman, J. D. "Environmental Control of Dormancy and Germination in the Seeds of Cenchrus longispinus (Hack.) Fern.," Weed Research 14:1–11:1974.

United States Department of Agriculture. Agricultural Research Service. Selected Weeds of the United States, 1970, reprinted by Dover as Common Weeds of the United States, 1971.

_____. _____. Germplasm Resources Information Network. Distributions for Pennisetum species available on line.

Wooten, Elmer Otis and Paul Carpenter Standley. Flora of New Mexico, 1915.

Photograph: Sandbur laying beside the road, 30 January 2011; burs are hidden among the leaves.

No comments: