Orobanche riparia

L. Turner Collins, Flora North America (Vol. 17)

Annual root parasite. Stem stout or slender, fleshy, 5–35 cm long, solitary or clustered, unbranched or rarely numerous branches. Cauline leaves reduced to scales, 7–10 mm long. Inflorescence a spike-like raceme, glandular pubescent; bracts mostly ca. 1 cm long, the distal ones shortened, narrowly oblong-lanceolate, pale lavender to dark purple. Flowers sessile or the proximal ones on short pedicels; calyces 7–11(–13) mm long, purple, deeply 5-lobed, the lobes lance-linear to linear-subulate, about equal in length, densely glandular pubescent; corollas (13–)15–22 mm long, constricted above the ovary, strongly curved at the constriction, the tube nearly horizontal, glandular puberulent or pubescent, persistent, the tube narrow or slightly flared distally, cream-white sometimes tinted with purple, upper lip ca. 5 mm long, erect, divided about half its length, the 2 lobes triangular-acute, lavender or purple, puberulent or densely pubescent with eglandular trichomes; lower lip 3–4 mm long, pubescent with eglandular trichomes, pale; stamen glabrous or with a few scattered hairs. Anthers glabrous or sparsely pubescent. Flowering mid-August to early October.

The species is found almost entirely on mixed sand and silt deposits on stream banks or sandbars of rivers including Ohio, Wabash, Meramec (near St. Louis), Platte, Canadian, Cimarron, and Rio Grande rivers (or tributaries). The hosts are annual members of Asteraceae, subtribe Ambrosiinae including Ambrosia trifida and Xanthium strumarium, and occasionally and Dicoria canescens. Alternate hosts are Nicotiana tabacum and N. glauca.

From Flora of Indiana (1940) by Charles C. Deam

A very local plant in Indiana. It has been reported from Jefferson and Vigo Counties and from the Lower Wabash Valley. Usually a parasite on the roots of Ambrosia trifida. I found it as a common plant on this host on the east bank of Goose Pond in Gibson County. Miss Edna Banta found it on the roots of tobacco plants in Jefferson County. In 1938 I found it in Knox County.

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Indiana Coefficient of Conservatism: C = N/A

Wetland Indicator Status: FACW