If you wonder where that pile of white, cotton-like fluff in your yard came from, look around to see if there are poplar trees nearby. If so, their seeds are the likely cause. The name "poplar" is commonly used to refer to the different species of trees in the Populus genus, which is part of the Salicaceae, or willow, family.
Poplar tree seeds, like most tree seeds, are dicotyledons, meaning they have two cotyledons -- the embryonic leaves growing inside the seed and the first leaves that emerge once the tree starts growing. The cotyledons also store food for the plant, giving it a head start until it can begin producing food on its own. The name "dicotyledon" can be shortened to dicot. Monocots, the other, less common type of seed, only have one cotyledon.
Capsules are a type of dry fruit. When the female flowers of poplar trees mature, they form capsules with seeds inside. When the capsule reaches maturity and splits open, it releases the seeds. Poplar capsules range in colour from brown to light green and have two valves containing several seeds. The number of seeds varies by species. On poplar trees, the capsules grow on catkins, which have several flowers grouped together in a thin, dangling group.
Poplar seeds are small and lightweight. They are oval-shaped, brown and smooth, with no lines or creases. The seeds are comose, meaning they have tufts of white, silky hair. This fluffy, cotton-like hair is why some poplar trees are also referred to as cottonwoods.
Most poplar seeds are dispersed by the wind, which can easily pick up and carry the seeds due to their lightness and the tufts of hair on the seeds. Water can also disperse the lightweight seeds by floating them to other locations. Because they are so easily dispersed, seeds can travel miles away from the parent tree.
Poplar seeds mature in the spring, but they are not viable for long. Once the seed ripens, it is only viable for two to four weeks. If the seed does not encounter favourable soil and moist conditions in that time, it will not germinate. Dried and frozen seeds can remain viable for approximately one year.