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https://www.sciencenews.org/article/why-dandelion-seeds-spread-wide
On any given dandelion, some seeds are destined to go north, while others are fated to fly east, south or west, and every direction in between. In effect, each dandelion seed is programmed to release for a wind coming from one direction and resists winds from other directions, according to research to be presented at the American Physical Society's Division of Fluid Dynamics in Indianapolis on November 20.
Dandelion seeds are susceptible to different wind directions depending on where they are on the seed head, says Jena Shields, a biophysicist at Cornell University. The feathery seeds on the side facing a breeze will let go most easily; the others hold on tens to hundreds of times tighter — until the wind shifts.
[...] Shields measured the force it takes to pluck dandelion seeds by supergluing a fine wire to the tufted ends and pulling them from the seed heads at various angles. This seed-by-seed study mimicked what happens when wind, or a child's breath, pushes them over. Because each seed is most susceptible to winds from distinct directions, it helps prevent seeds from all going the same way, Shields says, and may explain why the plants are so successful at spreading. Once blown off a dandelion, the umbrella-like tuft on a seed carries it on the breeze that pulled it away.
(Score: 2) by canopic jug on Sunday December 04 2022, @07:59AM
It's an interesting investigation in fluid dynamics, at least to me since I've wondered about that a little but never enough to dig into the matter: I've seen areas with many dandelions where there is usually a light to medium breeze, but not usually stronger, in one direction or another. When the seeds ripen there is usually a tuft remaining on the leeward side. The milder the breeze the larger the tuft.
Basically the individual seeds are sunken a little in very shallow pock mark on the head of the stalk which gives them a good grip. At low levels of air movement, the seeds detach only when a seed is bent past a certain angle and the little parachute helps the wind do that for most angles except those which are mostly down wind from the stalk head. Furthermore the parachutes on the seeds help create local turbulence so they can ride the breeze better [sciencenews.org].
What I'd like to know is how all subsequent flowers lie very low and flat to the ground if the first few blooms were mown. If you don't mow a patch, they'll grow as straight and as tall as needed to stand over the grass they are in, within limits of course. Yet once they are mown the new flowers go out sideways and hug the ground. In that case the stalks still rise but only a bit and only about a day before the seeds are released.
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