Weeds with feathery wind blown seeds
Annual herb with spreading taproot; stems bushy, much branched, 1/2 to 4 feet tall, 1 to 5 feet in diameter, rigid, spiny, spherical, often reddish-purple in age, young stems and leaves green and succulent.
Leaves: Leaves alternate, the first-formed leaves fleshy, cylindrical or awl-shaped, 7/16 to 2-1/2 inches long and less than 1/16 inch wide, with a pointed tip, the latter-formed leaves shorter, stiff, dilated and thickened at the base, ending in a hard sharp spine.
Flowers: Flowers June to October; flowers small, greenish, mostly solitary in the axils; petals none; sepals 5, papery and persistent; 2 bracts at the base of each flower are rigid, spine-tipped; fruit surrounded by the 5 enlarged sepals, each developing a fan-shaped, strongly veined wing on its back, 1/8 to 3/8 inch in diameter.
Fruit: Seeds numerous (to 250,000 per plant), top-shaped, 1/16 inch in diameter, with a yellowish coiled embryo, visible through the thin gray wall.
Cultivated and disturbed or degraded sites in grassland and woodland communities, and roadsides in any type of well-drained, uncompacted soil, however, it is most frequent in alkaline or saline soils within elevations that generally range below 8,500 feet.
Reproduces by seed; Russian thistle is a highly effective reproducer, after seeds mature in late fall, the plant stem separates from the root, the plant is then blown by wind; seeds, held in the leaf axils, fall to the ground as the plant tumbles.
Native to the Mediterranean region; Russian thistle aids in spreading fire; burns easily because stems are spaced in an arrangement that allows for maximum air circulation; dead plants contribute
to fuel load by retaining their original shape for some time before decomposing. In general appearance, this species could be confused with kochia. This species generally occurs as a weed in wildland areas of the Southwestern Region rather than as an invasive plant.
Activity | Dust storms, tumbleweeds and traveling seeds!
Windy days are part of the seasonal experience living in the Sonoran Desert. Dust storms commonly referred to as haboobs, form when a large mass of cold, unstable air moves swiftly across dry ground covered with loose silt and fine sand. These dust storms can be about a mile high, travel 200 miles and are most intense and frequent during the summer months.
Surprisingly, many plants rely on wind for dispersing its seeds. Wind provides ‘free transportation’ for a new plant to germinate (grow) away from the parent plant. This is important since seeds that are too close to the parent plant often will not have the resources (enough water and space) to grow.
Common plants that rely on wind to reproduce include desert milkweed, desert willow, birdcage primrose, cottonwoods and desert broom to name a few. The famous “tumbleweed” often seen blowing across the road during a dust storm, relies on wind as well. Did you know that tumbleweeds are not native to Arizona? They are actually a thistle from Eurasia.
Look closely at the following seeds. You will notice that some have feathery bristles, which allows them to be carried long distances by the wind. These seeds are also light and can lift off the ground easily. Some desert plants have a round shape when they dry and can roll, allowing their seeds to fall out onto the ground as they travel across the desert.
Desert Milkweed Seeds
Desert Broom Seeds
Desert Willow Seeds
Spending time outside observing wind and learning about seed dispersal is great activity for kids of all ages.
- Head to the Garden, a park or explore your neighborhood and ask your child if they can see the wind.
- Encourage them to explain how they know it is there even though they cannot really see it.
- Ask them if they can tell you which direction the wind is blowing. Ask them if it is difficult to tell which direction the wind is blowing.
- Encourage them to look for rustling leaves, swaying trees or palm trees. During your walk, collect seeds and see which ones move with the wind and which ones do not.
- Have fun and encourage movement by running with the wind and running against the wind. Which was easier? Have them stand still and wave their bodies like the wind. Then have them twirl and whirl like the wind.
Design your own imaginary seed that can travel by wind from the seeds collected. What will a seed need to have to move by wind? Wings? Lite weight? Encourage your child to be creative with their imaginary seed creation.
For older children, consider the following extension to conduct a seed dispersal experiment, mimicking an exploding seedpod like a cattail. Participants will need a balloon, small birdseed, a small cup, a funnel, a sharp pencil, butcher paper (or something similar), a ruler and a sheet of paper.
- Head outside and place the butcher paper on the ground.
- Blow up the balloon (this allows the seeds to flow more easily into the balloon.)
- Use the funnel to pour in a cup of the birdseed.
- Hold the balloon with the birdseed over the center of the paper on the ground. Use the pencil to pop the balloon.
- Use the ruler to measure how far the seeds traveled from the center of the paper to all four sides and use these measurements in the diagram.
- Use the blank sheet of paper to draw a diagram of where the seeds fell and label the surroundings. Include any trees or bushes nearby and where you stood and the distance the seeds traveled from the center.
After participating in these activities come to the Garden and enjoy Wind by Natasha Lisitsa and Daniel Schultz of Waterlily Pond Studio on display through Feb. 19.
Junglerice ( Echinochloa colona ) and feather fingergrass ( Chloris virgata ) seed production and retention at sorghum maturity
In Australia, junglerice and feather fingergrass are problematic weeds in sorghum. The high seed production potential of these weeds increases their seedbank in the soil and makes weed control practices more difficult and expensive, particularly when weeds have evolved resistance to herbicides. A study was conducted to evaluate the seed production and seed retention behavior of junglerice and feather fingergrass at sorghum crop maturity following four transplanting times: 0, 2, 4, and 6 wk after sorghum emergence. Averaged across years, junglerice and feather fingergrass produced 4,060 and 5,740 seeds plant -1 , respectively,when they were transplanted with the emergence of a sorghum crop. Seed retention ranged from 42% to 56% for junglerice and 67% to 75% for feather fingergrass when these weeds were transplanted from 0 to 4 wk after crop emergence. A positive correlation ( r = 0.75 for junglerice; r = 0.44 for feather fingergrass) was found between seed production and weed biomass in both weeds, indicating that larger plants produced more seeds than smaller plants. However, no correlation was found between weed biomass and seed retention for junglerice. A weak positive correlation ( r = 0.44) was found between feather fingergrass biomass and percent seed retention, indicating that seed retention was greater in larger plants compared with smaller plants. Our results suggest that feather fingergrass is a good candidate for harvest weed seed control (HWSC) tactics if crop harvest is timely. There is limited opportunity to use HWSC tactics for targeting junglerice seeds in sorghum crops, because most seeds dispersed before crop maturity. Additional research is required to evaluate seed retention levels of these weeds in other summer crops such as corn and soybean to determine the potential for HWSC for management of these species.