Liorhyssus hyalinus (F.) is a nearly cosmopolitan, polyphagous rhopalid, or scentless plant bug, that feeds mainly on flowers, fruits, and seeds of its hosts. Adults are known from numerous plants in diverse families, whereas nymphs develop on fewer species. Thirteen species of host plants were recorded for L. hyalinus during the sampling of grasses, forbs, subshrubs, and shrubs in the western United States (west of 100th meridian) from 2000 to 2015. The 11 new host records are Lygodesmia juncea, Machaeranthera tanacetifolia, Sonchus asper, Stephanomeria exigua, S. pauciflora, and S. thurberi (Asteraceae); Chamaesyce albomarginata (Euphorbiaceae); Erodium botrys and E. texanum (Geraniaceae); and Malva parviflora and Sphaeralcea ambigua (Malvaceae). The most common host (9 collections) was the adventive Erodium cicutarium, previously reported as a host in the Old World. Another previously known host was Sonchus oleraceus. Hosts of L. hyalinus in western states comprise four principal groups: latex-bearing (milky) composites of the tribe Cichorieae (Asteraceae); latex-bearing, mat-forming euphorbs or spurges (Euphorbiaceae); herbs and subshrubs of mallows (Malvaceae); and species of the stork's bill genus Erodium (Geraniaceae). Nymphs were observed on grasses (Poaceae) once: in a small, still-green colony of an undetermined species during prolonged drought in California. Based on fieldwork and a review of the literature, the common name hyaline grass bug appears to be a misnomer. The presence of adults on plant species that apparently do not support nymphal development is discussed in relation to the bug's bionomics, proximity to crop fields, and weather conditions. Although somewhat different definitions of “host plant” might be needed for different insect groups, a more consistent and restrictive interpretation of the term is recommended.