Cactodera galinsogae n. sp. (Heteroderinae) was isolated from dicotyledonous Galinsoga parviflora (Asteraceae) roots. It also reproduced on barley (Hordeum vulgare) and wild oats (Avena fatua) (Poaceae) and on other dicotyledonous weeds, notably Bidens odorata (Asteraceae). The samples were taken from a cultivated field of barley in the town of "La Raya", municipality of Singuilucan, Hidalgo, in the Central Valleys of Mexico. Cactodera galinsogae is characterized by the vulval cone of the females and the cysts are smaller than in most other species of this genus, with a straight neck, and the vulval cone with circumfenestra but without vulval denticles. The cysts are small (average length 523 µm), spherical or sub-spherical and light to dark brown with a straight neck, and with the transverse branching striae of the cuticle surface pattern of the midbody forming an interlaced pattern. The second stage juveniles have six pseudolips, and four lateral lines with incomplete areolation (non-areolated internal lines) on the side of the body. The eggs are retained in the females, although a gelatinous matrix (without eggs) is observed in some. The egg-shells, when observed under the scanning electron microscope, show a specific pattern of punctations. The males are cylindrical and small (average length 830 µm) compared to the other species of Cactodera. They adopt a 'C' shape when killed by heat, with 4-5 lip annuli on the irregular labial region. The excretory pore is located at the level of the esophageal gland lobe (distance from the anterior end to the excretory pore/L = 14.7%). The spicules are slightly curved and bifid.