Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
culmus, i, m. [kindr. with culmen], a stalk, stem, esp. of grain, straw, Varr. R. R. 1, 48, 3 (Cod. Vindob. culmen); Cic. Sen. 15, 51; Verg. G. 1, 111; 1, 317 al.
Of other plants: milii, panici, Plin. 18, 7, 10, § 52: holci, id. 27, 10, 63, § 90: lilii, Stat. S. 3, 3, 128.