Bupleurum chinense Seeds | Chai Hu, Growing Guide
LATIN NAME: Bupleurum chinense
COMMON NAME: Chai Hu
Plant Profile
Walk the genus and you notice how the leaf keeps its own counsel. Instead of the ferny, much-divided blade that marks most Apiaceae, Bupleurum holds a simple leaf with entire margins and parallel veins, its base often wrapped round the stem as a clasping collar. That single character is the quickest field mark for the whole group.
The flowers are tiny, yellow-green, and gathered into compound umbels that open through midsummer. The arrangement is unusual in one respect that matters at the bench: the umbel sits inside a ring of small leafy bracts, and each little umbellet carries its own inner collar, so a plant in flower reads as a set of nested crowns. The fruit that follows is a ribbed schizocarp, splitting into two halves with oil canals between the ribs.
Thorowax is a modest-looking plant that earns its keep twice: as a root crop dug at the end of its second or third season, and as a fine-textured filler for a gravel bed.
A good bupleurum root is pale grey-brown outside, with the fine lateral roots intact and the crown uncut, and it should still smell faintly of the volatile oil found in the outer tissue. Roots are washed, spread and dried whole rather than sliced, since slicing loses the volatile fraction quickly.
Plants grown for decoration are best left alone to flower. The blue-green foliage is fine enough to read as mist, the flat umbels hold their shape into late summer, and the dried seed heads stand through winter if the stems are left uncut.
Science & Biotechnology
The root stores oleanane-type triterpenoid saponins known as saikosaponins, chiefly saikosaponin a and saikosaponin d, with saikosaponin c and a family of closely related forms. They accumulate in the outer tissue of the root, which is why the thin skin is prized and why a brash handling of the root during digging can cost the grower.
Saikosaponin a and saikosaponin d are the parent compounds, and the b series arises largely through loss of a sugar unit and rearrangement during drying and storage. A grower who dries a root slowly in warm air therefore ends up with a different profile from one who dries it fast, and buyers of the dried drug test for that difference.
Hairy-root cultures of Bupleurum started with Agrobacterium rhizogenes have been used to follow how the saponins are assembled, and the cultures respond to methyl jasmonate and similar elicitors with a rise in saponin content.
Bupleurum root sits at the centre of several well-known prescriptions, among them the Minor Bupleurum Decoction and the free-and-easy wanderer powder, Xiao Yao San. Research on the root has followed the liver and the inflammatory pathways that these formulae were traditionally used to address.
Uses & Benefits
The root sold as bupleurum root comes from B. chinense in the north, while the southern drug is B. scorzonerifolium, and a third species, B. falcatum, fills the same role in Japan and Korea. They are separated on leaf width, root shape and on the branching of the root crown, and the northern drug is the one most commonly planted for the root trade.
Growing from Seed
Sieve a bed of loam and grit, aim for a neutral reaction, and site it in full sun where the ground drains fast. Scatter the seed thinly and cover it with a bare film of soil, no more than its own thickness, then water gently and keep the surface from crusting until the rows are up.
Thin to about 15 cm apart for a root crop, and further if you are growing the plants for flower. Handle seedlings early, because a taproot bent at planting stays bent, and every fork in a dried root is money lost at the buyer’s table. Weed while the plants are small and then leave the ground alone.
Autumn-sown plants overwinter as small rosettes and benefit from a gravel mulch to keep the crown dry. In a wet winter the root can rot where water sits, so raise the bed if the site is heavy. Cut the flowering stems off plants grown for root, and lift the roots in autumn when the tops begin to yellow.
Our Take
Bupleurum is rarely grown alone in my experience. It shares a bed well with the other dry-land roots of the Chinese repertory, and the sweet root of Chinese liquorice is the classic companion in the decoction tradition. If you want to compare species, the Japanese drug plant Bupleurum falcatum is grown from the same seed stall, and prepared roots are available as Radix Bupleuri root.
Related Reading
Gardeners who grow Chai Hu often pair it with these related subjects: