Global description
Oenothera stricta is a biennial or perennial herb, erect, sparsely branched, reaching up to 1 m in height. The leaves are simple, narrowly elongated, elliptical to linear, pointed ends, those of the base are arranged in rosette, sessile, alternate caulinary. The yellow flower is large (up to 7 cm diameter) with reflected sepals. The fruit is a narrowly elongated capsule with 4 valves. It contains many ellipsoids brown seeds.
Growth habit
Grass biennial or perennial, erect, sparsely branched, up to 1 m in height.
Underground System
Taproot.
Stem
The stem is sometimes reddish in colour. It has short stiff hairs (especially near the base) and longer hairs.
Leaf
The leaves of the base, arranged in rosette, are narrowly elliptic to obovate or nearly linear, with pointed end. They measure 8 to 15 cm long and 0.8 to 1.2, or even 2 cm wide. The stem leaves are sessile, simple and alternate. They are also narrowly elliptic to obovate, with wedged to rounded base, acute apex, serrated margin. They are 5 to 11 cm long and 0.5 to 1 cm wide.
Inflorescence
Flowers arranged in a very loose terminal cluster. The bracts (2-4 cm long and 0.5 to 1.5 cm wide) are sessile, oval to narrowly oval, truncate or nearly cordate base, with acute end. They are sometimes reddish in colour.
Flower
Regular tetramer flower. The free sepals (1.2 to 2 cm long and 0.3 to 0.7 cm wide) are reflected at flowering. The petals, obovate broad, 1.5 to 3.5 cm long, are yellow, then reddish, sometimes with a red spot at the base. They are spread out and follow a floral tube of 2 to 4.5 cm long, thinly covered with short straight hairs. Stamens (8) have unequal filament (whose length varies from 1 to2 cm) and anthers of 7 to 9 mm long. The ovary with 4 loculus containing many ova, is extended by a style of 3 to 6 cm long ending with 4 elongated stigmas arranged crosswise.
Fruit
The fruit is a capsule of 4 valves, oblong, narrow elongate, 2 to 5 cm long and 0.3 to 0.4 cm in diameter, often reddish. It contains many seeds.
Seed
Seeds broadly ellipsoidal, 1.4 to 1.7 mm long, are brown in colour.
