Horseweed
Conyza canadensis
from the link ☼
For a whole lot of information and pictures of various stages of growth see Va. Tech. Weeds
Horesweed is an annual that reproduces by seed. Young plants form a rosette with softly toothed and hairy leaves. Mature plants produce a 2- to 5-foot stem that is terminally brached. Stems are stout, erect, unbranched at the base with bristly hairs. Flower heads are numerous, small, in axillary panicles. Numerous small, white or pink flowers are produced on stem branches. Seeds are 1/16 inch long with numerous slender white bristles on one end. Horseweed grows quickly when the weather turns hot in late June and July. It can grow to over 6 feet tall. Horseweed prefers dry sunny locations and can be found growing near annual sunflowers on many roadsides in the Central Valley.