Etymology of “weed”
Tim Boucher

Proto-Weeds in 23,000 yr old Israeli site

The change from wild-type morphology to domestic-type happens when wild plants are sown repeatedly in cultivated fields, Weiss explains: Clearly the Ohalo people had been cultivating cereals for years.
Wild wheat and barley scatter their seed without trouble, as it were. “When humans cultivate these grains over a number of successive seasons, however, a change occurs,” says Weiss. “They develop a rough scar that locks the seed dispersal units together. Such plants cannot sow themselves.
This is the hallmark of domesticated, rather than wild-type plants.” These cereals were found mixed with 13 species of “proto-weeds” — ancient ancestors of the current weeds known to flourish in cultivated, single-crop fields — indicating that they grew together with food crops, and were unintentionally harvested together.

Full research paper: