Every spring the scene repeats itself: streets and parks are filled with white tufts that float in the air like out-of-season flakes. And every year, punctually, the accusation is made: blame the poplars. In fact, that association is wrong — and it’s worth understanding why.
What are those flakes really
The wads that invade cities are not pollen. They are called pappus and perform a purely mechanical function: to transport the poplar seeds through the wind, so that they are deposited far from the mother plant. It is a very widespread evolutionary mechanism in the plant world, known as anemochorous dissemination. Pappi are essentially fruits: structures of light cellulose, the same fiber that makes up cotton, completely devoid of allergenic properties.
The poplar pollens – the potentially annoying ones, even if they have low allergenic potential – had already been released weeks earlier, when the tree was still without leaves. Invisible to the naked eye, they had gone unnoticed. When the pappuses begin to fly, the poplar has already closed its reproductive season long ago.
Because then we feel worse precisely on those days
The answer is a classic case of apparent correlation. The period in which pappus saturates the air coincides with the intense flowering of grasses, among the most allergenic plants of all, which from April onwards release enormous quantities of pollen into the atmosphere – invisible, odourless, imperceptible. The symptoms are there, but the culprit is not seen. The white balls, on the other hand, are clearly visible: and it is on them that the blame instinctively falls.
However, there is an element that partially justifies the suspicion: pollen from other flowering species, or particles of fine dust produced by traffic, can adhere to the soft surface of the pappus. In this sense, pappus does not cause allergies, but can act as involuntary carriers, amplifying exposure to substances already present in the air. Added to this is a simple mechanical nuisance: when inhaled or in contact with the eyes, these flakes can irritate the mucous membranes independently of any allergic reaction.
The poplar in Italy
The poplar — Populus spp. — it is one of the most characteristic trees of the Po Valley, present along the rivers, on the banks of the lakes and widely cultivated both for ornamental purposes and by the paper industry. In Italy mainly four spontaneous species grow: the black poplar, the white poplar and the cypress poplar, among the best known, all capable of reaching considerable heights and flowering between February and April.
The spring snow phenomenon is produced exclusively by female specimens during fruiting. It is no coincidence that in urban plantations there is now a tendency to prefer male trees: the cypress poplar that can be seen along Italian roads is almost always in its male variant, physiologically incapable of producing pappus.
