Chelidonium majus is a brittle, herbaceous biennial that reaches 11-31 in. (30-80 cm) in height. Its stems are ribbed and branching. The lower parts of the branches are pubescent. When the branches or leaves are broken a yellowish-orange sap can be seen.
Foliage
The alternate cauline leaves can be up to 13 in. (35 cm) in length, with petioles measuring 0.75-4 in. (2-10 cm) long. The thin leaf blades are glaucous beneath, deeply 5-9 lobed and are irregularly dentate around the margins. The veins of the lower leaf surfaces have fine, short hairs.
Flowers
The bright yellow flowers are contained in axillary pedunculate umbels. The peduncle itself measures 0.75-4 in. (2-10 cm) long. Each flower has four obovate to oblong petals that measure about 0.4 in. (1 cm) wide. This plant usually flowers from May to June.
Fruit
The "lumpy" capsules are linear to oblong-shaped and measure 0.75-2 in. (2-5 cm) in length. Within the capsule are black seeds with reticulate pitting on their surface.
Ecological Threat
Chelidonium majus can become abundant in minimally managed habitats and can outcompete other native herbaceous plants. It is most often found in disturbed areas especially with moist soil. Conceivably its seeds could be moved to other habitats by ants.