Buddleja sessiliflora is a trioecious shrub or small tree 1.5 – 5 m tall, the trunk reaching < 7 cm diameter, bark is yellow-brown in colour and fissured. The young branches are subquadrangular, yellowish, the youngest sections tomentose. The leaves vary widely, those at the base ovate, 9 – 23 cm long by 5 – 14 cm wide, the margins serrate, whilst the upper leaves are lanceolate or narrowly elliptic, 5 – 15 cm long by 1.5 – 3 cm wide, the margins entire or irregularly serrulate. The upper surfaces of both are generally glabrescent. The yellow leafy-bracted inflorescences are 6 – 25 cm long, comprising sessile or short pedunculate heads 1 – 3 cm in diameter, each with 10–35 flowers. The scent of the flowers is generally regarded as unpleasant, 'like ammonia but sweeter'. Ploidy: 2n = 76.[5]