ragweed

noun

Etymology: From rag + weed. Compare Middle English ragwed (“butcher's broom”).

1. A plant of the genus Ambrosia. These weeds are particularly noted for producing pollen that triggers hay fever.

   “Fig. 1.—Spiculated pollens of ragweeds (ambrosias) low in protein. […] In the cocklebur (Xanthium americanum) and the rough wild elder (Iva ciliata), the spicules are shorter, being 0.7 and 0.5 microns, and the reaction is proportionately less active than with the ragweeds (ambrosias). […] While the grass pollens have so light a coat that they are frequently crushed in the ordinary process of mounting, the ragweed (ambrosias) pollen grains resist pressure between two glass slides carried to the point of crushing the glass.”

   “RAGWEED (Jeffogia Fingerolia) : The hayfever king, ragweed, brings tears to the eyes of grown men.”

2. A summer cypress, mock cypress (Bassia scoparia).