N-Methylmorpholine was isolated from the dried, ground seeds of Cassia occidentalis L. (coffee senna), an annual legume naturalized from the tropics that grows in waste areas of the southeastern and southwestern United States and whose roasted seeds are used as a coffee substitute (toxic when unroasted). The isolation involved extraction with ethanol containing 3% tartaric acid at 50-60°C, concentration, acidification with sulfuric acid, benzene extraction to remove nonpolar substances, basification with sodium hydroxide, chloroform extraction of the base, conversion to the hydrochloride salt, purification, and crystallization from 2-propanol. The compound's identity was confirmed by comparing its infrared spectra (peaks at 2480, 2620, 2695 cm⁻¹ for R₃NH⁺Cl⁻ and 1110 cm⁻¹ for C-O-C), mass spectra (m/e 101 corresponding to C₅H₁₁NO, with fragments at 71 and 43), melting point (208-208.5°C for the hydrochloride salt), and mixture melting point with synthetic N-methylmorpholine hydrochloride. This is the first reported isolation of N-methylmorpholine from the plant kingdom. Previous studies on C. occidentalis seeds identified toxic principles including toxic albumin, chrysarobin, toxalbumin, and anthraquinone derivatives; a prior toxic volatile base was uncharacterized due to low yield.