Ozone pollution also harms forests because it causes early leaf drop and lower growth rates. Ozone reacts with photosynthetically active cells on the upper surface of leaves typically causing an interveinal injury which is dark purple to black in color with distinct edges. Leaves are opposite, oval, and 2-10 inches long. The surface of the leaf is hairy beneath and smooth above. The leaf stem is short and thick.
Milkweed exudes a thick white sap from any cut or broken surface.
It also appears that milkweed may send up stems intermittently through the growing season. This may result in stems being at different life stages throughout the summer. Milkweed is common in fields, meadows, and along roadsides. This species is found from New Brunswick to Saskatchewan, south to Georgia and Tennessee and west to Iowa and Kansas. Milkweed flowers from June to August.