Black-eyed Susan (Thunbergia alata) is regarded as an environmental weed in New South Wales and Queensland. It is also a potential environmental weed or “sleeper weed” in Western Australia and the Northern Territory.
A long-lived vine growing up to 5 m in height. Its slender stems are green and hairy when young. Its paired leaves (2-8 cm long and 1-4.5 cm wide) are borne on narrowly winged stalks. Its tubular flowers (3-4 cm wide) are borne singly in the upper leaf forks on stalks 30-95 mm long. These flowers are usually orange or yellow with a black throat and have two leafy bracts at their bases. Its fruit has a rounded base (5-10 mm across) containing the seeds and an elongated beak (9-15 mm long).