Herb to 150 cm tall, with appressed hairs. Stems unbranched, erect. Leaves basal and along stems; basal leaves divided; stem leaves divided, but less so. Capitula many in corymbs at apex of stems; summer. Ray florets with ligules about 1mm long, yellow. [A. eupatorium M. Bieb.]
Other yellow-flowered species include:
A. ageratum L., Sweet Yarrow, from the W Mediterranean, which has toothed stem leaves - 'Salmon Beauty' has flowers salmon, paling to creamy yellow;
A. clypeolata Sibth. & Sm. from the Balkan Peninsula to Romania, which has gland-dotted leaves and short ligules;
A. coarctata Poir. from the Balkan Peninsula to Ukraine,which has much-divided leaves and long ligules;
A. tomentosa L.,Woolly Yarrow, from SW Europe, which is a woolly herb with stem leaves with leaflets in more than 1 plane, and short ligules - 'Aurea', a cultivar of this species, is a compact, mat-forming dwarf plant with woolly leaves and dark yellow flowers.
Source: (2002). Asteraceae. In: . Horticultural Flora of South-eastern Australia. Volume 4. Flowering plants. Dicotyledons. Part 3. The identification of garden and cultivated plants. University of New South Wales Press.