Name: Tagetes patula
A commonly grown, non-invasive french variety. Originally a sacred flower of the Aztecs.
Beneficial in the garden?
You bet. The roots repel nematodes and the flowers can act as a decoy or, strawman for Japanese beetles to protect your other crops.
… marigolds are best known for their ability to suppress plant-parasitic nematodes. Marigold roots release the chemical alpha-terthienyl, one of the most toxic naturally occurring compounds found to date (Gommers and Bakker, 1988). 1