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 two best species are B. salicifolium and B. speciosum or cordifolium, both 3-5 ft. high, with golden-yellow or orange flower heads 3-5 in. across. They grow in any garden soil, and are effective on the banks of lakes, streams, etc. They are easily increased by seeds and division. The trade is chiefly in the roots, but the plants are good for cut bloom.