Bright yellow poppy flowers are produced from spring to early summer on the greater celandine poppy (Chelidonium majus), a hardy perennial that thrives in shaded locations with moist soils. This is another example of a woodland plant that completes its growth and starts to go dormant during the heat and drought of mid to late summer. All parts of the plant contain chemicals that can alternate between medicinal and toxic, depending on the dose and the size and sensitivity of the patient. It has a long history of medicinal use in Europe and western Asia, but the yellow-orange sap has been known to cause allergic dermatitis.