Wild and Domesticated Oats

One or the other or both wild species, common (Avena fatua) or slender (A. barbata) wild oats are extremely widespread all along the Pacific Coast. They can be found in vacant lots, roadsides, pastures, and yes, even in our beautifully kept native plant gardens. This doesn’t mean that we’re bad gardeners, just that this genus produces very effective weeds.

Identifying Wild Oats

Wild oats are members of the grass family (Poaceae or Gramineae). Oats have some of the largest flowers in this family of otherwise tiny to minute flowers.

Parts of Oats (Avena spp.)

Parts of Oats (Avena spp.)

Their parts are almost large enough to be seen with the naked eye. Individual grass flowers are aggregated into tiny clusters (spikelets). The spikelets are the readily visible units hanging down in the photograph and drawing.

Each oat spikelet consists of two large scales (bracts or more specifically glumes) surrounding two to three small flowers called florets. Each floret contains the 3 male organs (stamens) and a single pistil consisting of a basal ovary and two feathery stigmas. The stamens and pistils can’t be seen in the drawings or photo as they are totally hidden between to additional bracts.

The outer (and the only one visible) is the canoe-shaped lemma and a totally surrounded, thin palea. There are no recognizable sepals or petals. In the wild oat species, a stout bristle arises from the back of the lemma. This bristle is known as an awn. After the pistil is pollinated, its single seed matures and fuses to the inner ovary wall to become the unique fruit produced only by the grasses (caryopsis or grain).

The seed coat and ovary walls, when removed from the grain, are the bran we can buy at grocery and health food stores. In oats, the outside of the developing grain adheres to the inside of lemma and palea. This means that seed dispersal in oats (as well as most other grasses) is actually floret dispersal. The awn plays a vital role in this dispersal. The long, stout awns are bent in the middle; they bend or straighten depending on moisture availability. When it is moist, the awns absorb water and straighten at the bend. This causes the floret body (including enclosed seed) to be pushed forward. When it is dry, the awn flexes at the bend. Why doesn’t it pull the floret back? Notice the short, backward oriented “hairs” at the base of the floret. As the floret dries, these flip out and prevent it from being pulled backwards. Thus the floret is consistently pushed forward until it buries itself under a clod or it falls into a crack in the soil. Either way, the process both disperses and plants the oat seed.

Local Oats

There are three species of oats listed in Hoover’s SLO County flora. Two of the species possess a moderate to stout awn. These are the slender oat (Avena barbata) and the common oat (A. fatua). The third species in found occasionally along road sides and in fields where it had been grown. It is the domesticated oat (A. sativa). Domesticated oats produce larger grains and either totally lack an awn or if awns are present, they are weak. The lack of an awn would make the domesticated oats much better for animal feed.


The origin of oats is somewhat controversial. It is for sure, Old World and domestication most likely took place somewhere in the area surrounding the eastern Mediterranean Sea. It is rarely mentioned in literature of the early cultures of this area and then only as animal feed. It probably didn’t stack up well against the dominate grains of the area, wheat and barley. It seems to have had better acceptance further north and east in Central Eastern Europe and adjacent Western Asia. Here it became quite important, but not much as a human food but the mainstay of horse diet. It is from this area that the first mounted soldiers arose and horses allowed them readily to conquer the surrounding “horseless” peoples.

The conquering of horseless cultures by horse-mounted armies was repeated whenever it occurred. It even was a factor in Spain’s defeat of the Aztecs and Incas. Interestingly, the re-introduction of the feral horses into North America apparently caused the then agricultural Great Plains Native Americans to become mobile buffalo hunters. Why all this discussion of the horse? Because it was probably the need to bring grain on ships to feed the horses that introduced oats into California and beyond.

Uses of Oats by the Chumash

According to Jan Timbrook, the Chumash used the grains of wild oats and chia (Salvia colunbariae) seeds in a concoction. Wild oats (along with any native grasses growing with them) were beaten or striped into baskets. The chaff was beaten off with a mallet against rocks. The flour was separated from the chaff by winnowing. The flour was mixed with water and chia was added. It provided both energy and protein.

Controlling with Herbicides

There’s one more human-wild oat interaction worth mentioning. The July 2, 2011 Science News reports that herbicide resistant wild oats infects at least 4.9 MILLION hectares. This is over 1 million hectares more area than the second place plant water hemp.

First off, wild oats are not particularly “naturally” resistant to herbicides. Second, the article discusses herbicide resistance that is transferred to wild (weedy) plants from genetically modified crops. The way emphasized in the article, is via transfer of the herbicide resistant genes from genetically engineered crops to the weed via ordinary transfer of pollen. The crops are engineered to have a high tolerance for a specific herbicide. Then the farmer is assured that he may use large amounts of the herbicide to kill weeds without affecting the crop.

Unfortunately, many plant species can transfer pollen BETWEEN DIFFERENT species. Once the gene for herbicide resistance is in the weed, then it will spread rapidly via ordinary natural selection processes. When herbicides are applied wholesale as they are in modern monoculture agriculture, a few individuals that received the genetically modified gene are more likely to survive and produce seedlings that also carry the gene and are therefore resistant also. These seedling grow up and produce more and more resistant plants at an ever increasing rate. If you remember much about evolution, you can see that farmers are both supplying the source of the gene as well as applying a strong selection pressure for the spread of the resistance gene. The last is the same process, by the way, that creates antibiotic resistant microbes when we over use antibiotics. Only microbes often do it in a shorter time due to their faster reproductive rate.

The article talks primarily about a class of herbicides known as glyphosates which is found in a wide variety of herbicides including Roundup. It is this component that crop breeders have been adding to the genome of crops. The article talks primarily about resistance in and around crop fields, especially around grain fields. I suspect Roundup and Fusilade work in your garden because resistance is not universal. It just hasn’t reached isolated areas like your garden. Let’s hope it never does! But I hope it does raise a red flag about over use of any chemical pesticide. There is no genetic resistance to mechanical pulling of weeds!

by Dirk Walters, illustrations by Bonnie Walters | Dirk and Bonnie Walters are long-time CNPS-SLO members, contributors, and board/committee participants. In addition to his work at Cal Poly, Dirk is the current CNPS-SLO Historian.