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..
Usually low annual biennial or perennial caulescent herbs, with prostrate or erect stems. Leaves alternate, sinuate or pinnatifid. Flowers perfect, yellow, axillary, or sometimes in terminal spikes, nocturnal; buds erect. Calyx-tube elongated, sometimes filiform, terete; calyx-segments 4, finally reflexed, deciduous. Petals 4, spreading. Stamens 8, equal in length; filaments filiform; anthers linear. Ovary 4-celled, elongated; united styles filiform; stigma deeply 4-cleft; ovules numerous, in 2 rows, ascending. Capsules usually narrowly cylindric, sometimes slightly tapering, spreading or ascending, obtusely 4-angled, loculicidal. Seeds numerous, in 2 rows, terete, crowned by a tubercle. [Name in honor of Rud. Raimann, a monographer of this family.]
Glabrous or sparingly hirsute-pubescent; seeds Oitted.
Flowers in terminal bracted spikes.
Oenothera humifusa Nutt. Gen. 1: 245. 1818.
Oenothera sinuata var. humifusa T. & G. Fl. N. A. 1: 494. 1840.
Raimannia humifusa Rose, Contr. Nat. Herb. 8: 331. 1905.
Spreading and decumbent or ascending, branched from the base and usually also above, silvery-pubescent with white appressed or ascending hairs; stems 8'-18' long. Leaves lanceolate to oblanceolate, sessile or narrowed into a petiole, acutish or sometimes obtuse at the apex, ą-2' long, repand-denticulate, the lower pinnatifid; flowers axillary, yellow, nocturnal, 6"-15" broad; calyx-lobes linear, obtusish, shorter than the tube, somewhat spreading; capsule linear, 6"-12" long, about 1 1/2" thick, very pubescent; seeds striate longitudinally.
Oe. minima Pursh, Fl. Am. Sept. 262. pl. 15. 1814.
R. laciniata Rose, Contr. Nat. Herb. 8: 330. 1905.
Decumbent or ascending, simple or sometimes branched, 4'-2 1/2° high, glabrous or sparingly hirsute-pubescent. Leaves sessile or the lower petioled, oval-lanceolate or oblanceolate, acute or obtusish at the apex, sinuate-dentate or often pinnatifid, 1'-2' long; flowers axillary (or on small plants sometimes solitary and terminal), 6"-2' broad; calyx-lobes linear-lanceolate, reflexed, much shorter than the slender tube; capsule linear, 1'-1 1/2' long, about 1" thick, more or less pubescent, straight or curved upward; seeds strongly pitted.