Chelidonium majus

,... commonly known as greater celandine or tetterwort, a herbaceous perennial plant, the only species in the genus Chelidonium.
The flowers consist of four yellow petals, each about 1 cm long, with two sepals. A double-flowered variety occurs naturally. The flowers appear from late spring to summer.
The whole plant is toxic in moderate doses as it contains a range of isoquinoline alkaloids but there are numerous therapeutic uses when used at the correct dosage. The main alkaloid present in the herb and root is coptisine. Other alkaloids present include methyl 2'-(7,8-dihydrosanguinarine-8 yl)acetate, allocryptopine, stylopine, protopine, norchelidonine, berberine, chelidonine, sanguinarine,chelerythrine, and 8-hydroxydihydrosanguinarine.
The chemicals in greater celandine might slow the growth of cancer cells.