Prionosciadium thapsoides (DC.) Mathias

Prionosciadium thapsoides (DC.) Mathias, Brittonia2: 245. 1936.
Ligusticum dubium H.B.K. Nov. Gen. & Sp. 5: 19. 1821. Not L. dubium Spreng. 1806.
Elaeoselinum thapsoides DC. Prodr. 4: 215. 1830.
Imperatoria mexicana Hort. Chels.; G. Don, Gen. Syst. 3: 336. 1834; Steud. Nom. Bot ed 2 1:
805. 1840. Angelica mexicana Vatke, Ind. Setn. Hort. Berol. 1876. app. 2. no. 12. 1876. Prionosciadium mexicanum S. Wats. Proc. Am. Acad. 23: 275. 1888. Prionosciadium Seleri Rose, Contr. U. S. Nat. Herb. 8: 335. 1905. Prionosciadium moschalum Rose, Contr. U. S. Nat. Herb. 8: 335. 1905. Prionosciadium Palmeri Rose, Contr. U. S. Nat. Herb. 10: 130. 1906. Plants stout, 1.5-4 m. high, the foliage and inflorescence more or less hispidulous; basal leaves deltoid in general outline, excluding the petioles 2.5-3.5 dm. long, 1-2-ternate to 1-2pinnate, the leaflets lanceolate to oblanceolate, obtuse or acutish at the apex, tapering or abruptly confluent at the base, 3-8 cm. long, 0.8-3 cm. broad, crenate to crenate-serrate, the leaflets confluent into the narrow, entirewinged, secondary rachis, the primary rachis essentially unwinged; petioles 1-3 cm. long; upper cauline leaves opposite, ternate with inconspicuous sheaths; inflorescence of a series of opposite umbels, the terminal whorled; peduncles stout, 2.5-10 cm. long, subtended by leaves; involucre wanting or of 1-several filiform bracts about 5 mm. long; involucel of several filiform bractlets 3-6 mm. long, puberulent; fertile rays 17-25, spreading, subequal, 2-3 cm. long, or 3-4 cm. long in some terminal umbels; fertile pedicels 2-4, 2-4 mm. long; calyx-teeth obsolete; flowers greenish-yellow or purple, the ovary hispidulous to glabrate; fruit oval, retuse at apex and base, 9-14 (16?) mm. long, 6-10 mm. broad, glabrous, the dorsal ribs short-winged, the lateral, broadly thin-winged, the wings equaling or a little broader than the body; oil-tubes 2-4 in the intervals, 3-6 on the commissure; seed-face involute.
Type locality: "In Mexico circa Sanctum-Angelum," probably Hahn. Distribution: Zacatecas and Mexico to Guatemala (Pur pas 7448, Seler 3106).

Prionosciadium thapsoides is a plant species native to the States of Veracruz and México, in the República de México, as well as Guatemala.

Prionosciadium thapsoides is a biennial herb with a large taproot. Leaves are bipinnately compound, the leaflets pinnately lobed with broad obovate lobes. Flowers are white, borne in dense compound umbels at the top of the flowering stalk.

Chemical studies have revealed the existence of several new dihydrofurochromones in the roots.