The title is the Latin name for common ragweed, a plant known for causing allergies, and the poem seems to start from that familiar misery. The speaker sits by an open window with clogged sinuses and red-rimmed eyes, the classic signs of hay fever. Nothing is said about the plant at first, so we only feel the symptoms.
Then the poem turns. It describes what happens after the wind carries the pollen: the female flower becomes a prickly burr holding a single arrowhead-shaped seed. The language shifts from the body to botany, calm and precise.
That shift is what makes the poem interesting. The speaker's discomfort and the plant's reproduction are really the same event seen from two sides. There is no complaint, only a quiet, almost amused detachment. The mood is still and observant, and the poem ends on the small, sharp image of the seed, as if the plant has the last word.