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.
Two species - B. cordata (fig. 185) and B. microcarpa, both natives of China and Japan, have become popular plants of late years, and are in every hardy-plantsman's catalogue. They are exceedingly vigorous growers, but the trade in them is strictly confined to the roots, although the stems, leaves, and plumes of whitish blossom are also useful for cutting. The plants grow in any except the worst and sourest soil, in shade or sunshine, and cannot be suppressed. They are easily increased by pieces of the root in spring, but will also come up like weeds from seed. The leaves are very large, deeply lobed, and very ornamental, with a white under surface, the fleshy fistular stems being often over 1 in. in diameter, and often 10-12 ft. high.