Yarrow is the plant that taught a hemisphere how to decide. Fifty of its dried stalks, sorted by hand, are the oldest randomiser of the Yijing — but long before it was an oracle it was a plant, and a strange, exact one. What stands on the plate to the left was not photographed. It was grown: a single 32-bit number, run forward through the rules that describe a real Achillea millefolium, until a whole stalk fell out. Sow the same number again and the same plant returns, leaf for leaf, forever.
The epithet millefolium — “thousand-leaf” — is barely an exaggeration. Each leaf is lanceolate only in silhouette; up close it is cut two or three times over (bipinnate to tripinnate) into dozens of thread-fine segments, so that a single leaf carries scores of leaflets and a whole plant carries, plausibly, its thousand. The texture is soft, almost feathery, grey-green and faintly hairy, and aromatic the instant it is crushed. Leaves are set alternately up the stem at the golden divergence of ≈137.5°; the basal leaves are largest and stalked, the stem (cauline) leaves smaller, stalkless, and half-clasping — so the plant tapers in leaf as it climbs.
The flowering stem is erect, tough, and faintly furrowed — angled rather than round — usually unbranched until the inflorescence, and lightly woolly toward the top. Dried, these stems are straight, light, and strong, which is precisely why, half a world from where yarrow grows wildest, fifty dried stalks became the counting-rods of the Book of Changes. The plant of staunched wounds — Achillea for Achilles, who is said to have dressed his soldiers' wounds with it; hence woundwort, soldier's woundwort, staunchweed, nosebleed-plant — became the plant of decisions. Its odds, cast in stalks rather than coins, are still weighted the old, lopsided way next door at /yijing.
What looks like a single flat bloom is a corymb: a crowd of small flower-heads whose lower branches are stalked longer than the upper, so every head is lifted to nearly the same plane — a landing-pad built for pollinators. And each “head” is itself a crowd. In the Asteraceae fashion, a capitulum gathers a ring of (typically five, occasionally three to eight) broad white ray florets — the false “petals” — around a button of ten to thirty tiny disc florets, the whole cupped in rows of dry, membranous-margined bracts. Dozens of these heads make one corymb; the eye, generously, reads the dozens as one.
Most wild populations are chalk-white. Rose and pink morphs occur naturally and are selected hard in gardens, where deep madder cultivars are common; the specimen at left is white.
The drawing is not a picture so much as a hypothesis about a plant: a small set of botanical rules, run forward from a seed. Phyllotaxis places the leaves up the stem, alternating at the golden angle and tapering in size toward the top. The leaf rule builds each leaf as a bipinnate rachis — so many pinna-pairs, each split into so many filaments; their product is the “thousand.” The corymb rule resolves a handful of primary branches onto one upper plane to make the flat top, then scatters the heads across its width. The capitulum rule draws each head's ray florets around the modal five, on an ochre disc. The morph rule paints the rays white, with a minority struck rose. Every value the rules chose for this specimen is listed under the plate — and because the seed is the only input, the plate is a permalink: ?seed=… grows this exact plant anywhere, any time.