Beneficial weed

For example, Parthenium hysterophorus which is native to Northern Mexico and parts of the US, has been an issue for years due to its toxicity and ability to spread rapidly.

In the past few decades though research has found that Parthenium hysterophorus has been used in traditional medicine to treat inflammation, pain, fever, neurological disorders and diseases like malaria dysentery.

Some beneficial weeds release volatile organic compounds that mask the scents of nearby plants, as with alliums and wormwood; others imitate the pheromones of pest insects and confuse them, as with ground ivy, oregano, and other mints.

[10] These pests: Some "weed" species, such as subterranean clover (Trifolium subterraneum L.), have been found to be specifically beneficial against pests targeting crops of common cabbage (Brassica) species, reducing insects by 39%-100% on brassica plants when they were sown surrounded with clover as compared to when surrounded by bare soil.

Many plants can grow intercropped in the same space because they exist on different levels in the same area, providing ground cover or working as a trellis for each other.

[16] Certain plants can be affected by a chemical emission through their roots or air, slowing their growth, preventing seed germination, or even killing them.

White clover is included in some grass seed mixes, because it is a legume that fixes soil nitrogen with help of mycorrhiza
Dandelions benefit neighboring plant health by bringing up nutrients and moisture with their deep tap roots.
Crow garlic , like any Allium , masks scents from pest insects, protecting neighboring plants [ citation needed ]
Queen Anne's Lace provides shelter to nearby plants, as well as attracting predatory insects that eat pests such as caterpillars, and may boost the productivity of tomato plants.