Cutleaf evening primrose

Oenothera laciniata

This plant is an annual about ½–2' long that often sprawls across the ground, or it is weakly ascending (particularly near the tips of its branches). Small plants are usually unbranched, while larger plants produce lateral stems occasionally. Each stem is terete, light green, and more or less hairy. Along each stem, there are alternate leaves up to 4" long and 1" across. The leaves are oblong-lanceolate to oblong-oblanceolate and pinnatifid; they are hairy, although less so along their  upper surfaces. The middle to upper leaves are sessile, while the lower leaves have short petioles. From the axils of the middle to upper leaves, there develops individual flowers that are sessile. Each flower spans about 1" across when it is fully open, consisting of 4 yellow petals, a narrowly cylindrical calyx (about 2" long) with 4 narrowly triangular lobe-segments at its apex, a narrowly cylindrical ovary/fruit (about 1–1½" long), 8 stamens, and a central united style with cross-shaped stigmata. The flowers bloom at night and become closed during the morning. Even though it appears that each flower has a stalk-like pedicel about 3" long, this is actually the narrowly cylindrical calyx and ovary/fruit of the flower. The lobe-segments of the calyx hang downward. The blooming period occurs from late spring to mid-summer and lasts about 1½–2 months. Only a few flowers are in bloom at the same time. After pollination of a flower, the entire calyx becomes pale salmon pink and falls off the fruit. The cylindrical fruit (or developing seed capsule) is straight to slightly curved and ascends upward; it is terete, slightly 4-ribbed, and more or less pubescent along its length. This plant reproduces by reseeding itself; the surfaces of the small seeds are pitted.

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