1. Spinacia oleracea Linnaeus, Sp. Pl. 2: 1027. 1753.
Stems leafy, 1-5(-10) dm. Leaves gradually becoming smaller distally; blade oblong, base cuneate. Bracteoles orbicular-obovate, usually wider than long, apex with divergent spine or smooth. 2n = 12.
Flowering spring-fall. Waste areas; 0-1500 m; introduced; Calif., Conn., Maine, Mass., N.H., N.Y., N.C., Ohio, Oreg., Pa., R.I., S.C., Va., Wash.; Eurasia; n Africa.
Reports of populations in Canada and inland areas of the United States appear to be from gardens where the plants do not persist without benefit of cultivation.
Spinach is an important and widely cultivated crop of unknown origin, though known from the Mediterranean region since ancient times. The plant is prized as a rich source of vitamins, calcium, iron, and antioxidant carotenoids, but, if ingested in excessive amounts, the high concentration of oxalates in the leaves can be toxic by inhibiting the absorption of calcium. The cultivated form named var. oleracea has spiny seeds and tends to be more cold hardy than var. inermis, the smooth-seeded variety that is more tolerant of warm weather.