This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The best-known species are the Southernwood, A. Abrotanum, a fragrant shrubby plant, 2-4 ft. high, also known as "Lad's Love" and "Old Man". It has divided grey-green leaves, and small yellowish flowers. There is a variety, Tobolskiana, larger in all its parts. A. lactiflora grows 4-6 ft. high. It is a noble-looking plant with branching sprays of creamy flowers borne well above the grey-green leaves in August and September. It flourishes in any soil and is even excellent as a bog plant. Other good species are holosericeus and lanata, both with silvery leaves.