Orobanche uniflora L.

One-Flowered Cancer-Root

© SRTurner

Family - Orobanchaceae

Habit - Annual holoparasitic forb, lacking chlorophyll.

Stems - To 6 cm, 3-8 mm in diameter near base, not thickened, somewhat succulent, tan to brown or yellow-brown, often with scattered branches.

	Stems.
© SRTurner

Leaves - Scale-like, densely spirally alternate near base of aerial stem, appressed, broadly ovate.

	Leaves.
© SRTurner

Inflorescences - Usually solitary terminal flower. Flower stalks 3-16 cm long, erect, tan, densely short glandular-hairy.

Flowers - Calyces 5-10 mm long, the lobes triangular, acuminate, slightly longer than the tube. Corollas 14-24 mm long, erect in bud but later becoming somewhat deflexed, cream-colored to violet, with 2 yellow pleats in the throat, the lobes broadly obovate to oblong or nearly circular, rounded or broadly and bluntly pointed. Stamens 4, usually included. Style included or slightly exserted, the stigma capitate to slightly concave, somewhat 2-lobed.

	Flowers.
© SRTurner

	Flowers.
© SRTurner

	Corolla lobes.
© SRTurner

Fruits - Ovoid capsules, 9-12 mm long, tapering abruptly to the persistent style, dehiscing longitudinally. Seeds numerous, minute.

	Fruit.
© SRTurner

	Fruit (remnant corolla removed).
© SRTurner

	Sectioned fruit with seeds.
© SRTurner

Flowering - April - June.

Habitat - Forests, prairies, calcareous glades and bluffs.

Origin - Native to the U.S.

Lookalikes - None.

Other info. - This attractive little plant is often overlooked, being small and not very showy. It is found throughout most of Missouri except for the Mississippi Lowlands division and possibly the extreme northwest. It also ranges across most of the U.S. but with an unusual distribution, being mainly concentrated in three regions: western, northeastern, and Midwestern. It is largely absent from large portions of the Plains states.

Like all members of its genus, Orobanche uniflora is holoparasitic, lacking chlorophyll and deriving all of its nourishment from other plants. Confirmed hosts in Missouri include various species of Ostrya, Potentilla, Quercus, Rudbeckia, Solidago, and Symphyotrichum. Host specificity is poorly developed and this is certainly only a partial listing.

The genus Orobanche derives from the Greek, and roughly means "vetch-strangler." The common name "cancer root" apparently refers to the plant's fancied cancer-like parasitism rather than any connection with human cancers.

Photographs taken at Engelmann Woods Natural Area, Franklin County, MO, 4-27-2015, Danville Conservation Area, Montgomery County, MO, 4-18-2017, and Don Robinson State Park, Jefferson County, MO, 4-26-2019 (SRTurner).