This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Low branching annuals, with ternately divided finely dissected leaves, the ultimate leaf-segments linear, spatulate, or oblong, and small white flowers in terminal sessile or pedurr-cled slender-rayed umbels. Involucels of a few linear or dissected bracts. Calyx-teeth obsolete. Fruit ovate to oval, laterally flattened, strongly ribbed, the ribs tuberculate or spinulose-tuberculate; pericarp very thick and dense; oil-tubes solitary in the intervals, and 2 on the commissural side. Styles and conic stylopodium short. [Greek, sand-parsley.]
Two known species, of the southwestern United States and Mexico, the following typical.
A diffusely branched herb, 6'-15' high, the angled branches, rays of the umbels, and pedicels, rough. Lower leaves slender-petioled, the upper sessile, or nearly so, all dissected into linear obtuse or acutish segments about 1/2" wide; involucre usually of 1 dissected leaf or more; involucel-bracts few, entire, or dissected; longer rays of the umbels 1' long in fruit, or less, the shorter ones often 1-flowered; fruit ovate, 2"-2 1/2" long, narrowed above, 1" wide, or a little more, the ribs rather strongly tubercled, or even spinulose.
In sandy soil, Kansas to Texas. April-May.