Evening-Primrose, Night Willow-herb – Flowers

(Onagra biennis)

(OEnothera biennis of Gray)

Flowers—Yellow, fragrant, opening at evening, 1 to 2 in. across, borne in terminal leafy-bracted spikes. Calyx tube slender, elongated, gradually enlarged at throat, the 4-pointed lobes bent backward ; corolla of 4 spreading petals ; 8 stamens ; 1 pistil ; the stigma 4-cleft. Stem: Erect, wand-like, of branched, 1 to 5 ft. tall, rarely higher, leafy. Leaves : Alternate, lance-shaped, mostly seated on stem, entire, or obscurely toothed.

Preferred Habitat—Roadsides, dry fields, thickets, fence-corners.

Flowering Season—June—October.

Distribution—Labrador to the Gulf of Mexico, west to the Rocky Mountains.

Like a ball-room beauty, the evening primrose has a jaded, bedraggled appearance by day when we meet it by the dusty roadside, its erect buds, fading flowers from last night’s revelry, wilted ones of previous dissipations, and hairy oblong capsules, all crowded together among the willow-like leaves at the top of the rank growing plant. But at sunset a bud begins to expand its delicate petals slowly, timidly—not suddenly and with a pop, as the evening primrose of the garden does.

Now, its fragrance, that has been only faintly perceptible during the day, becomes increasingly powerful. Why these blandishments at such an hour ? Because at dusk, when sphinx moths, large and small, begin to fly (p. 249), the primrose’s special benefactors are abroad. All these moths, whose length of tongue has kept pace with the development of the tubes of certain white and yellow flowers dependent on their ministrations, find such glowing like miniature moons for their special benefit,when blossoms of other hues have melted into the deepening darkness, If such have fragrance, they prepare to shed it now. Nectar is secreted in tubes so deep and slender that none but the moths’ long tongues can drain the last drop. An exquisite, little, rose-pink twilight flyer, his wings bordered with yellow, flutters in ecstasy above the evening primrose’s freshly opened flowers, transferring in his rapid flight some of their abundant, sticky pollen that hangs like a necklace from the outstretched filaments. By day one may occasionally find a little fellow asleep in a wilted blossom, which serves him as a tent, under whose flaps the brightest bird eye rarely detects a dinner. After a single night’s dissipation the corolla wilts, hangs a while, then drops from the maturing capsule as if severed with a sharp knife. Few flowers, sometimes only one opens on a spike on a given evening—a plan to increase the chances of cross-fertilization between distinct plants; but there is a very long succession of bloom. If a flower has not been pollenized during the night it remains open a while in the morning. Bumblebees now hurry in, and an occasional humming bird takes a sip of nectar. Toward the end of summer, when so much seed has been set that the flower can afford to be generous, it distinctly changes its habit and keeps open house all day.

During our winter walks we shall see close against the ground the rosettes of year-old evening primrose plants—exquisitely symmetrical, complex stars from whose centre the flower stalks of another summer will arise.

Floriform sunshine bursts forth from roadsides, fields, and prairies when the Common Sundrops (Kneiffia fructicosa)—formerly OEnothera fructicosa—is in flower. It is first cousin to the similar evening primrose of taller, ranker growth. Often only one blossom on a stalk expands at a time, to increase the chances of cross-fertilization between distinct plants; but where colonies grow it is a conspicuous acquaintance, for its large, bright yellow corollas remain open all day. Bumblebees with their long tongues, and some butterflies, drain the deeply hidden nectar; smaller visitors get some only when it wells up high in the tube. As the stigma surpasses the anthers, self-fertilization is impossible unless an insect blunders by alighting elsewhere than on the lower side, where the stigma is purposely turned to be rubbed against his pollen-laden ventral surface when he settles on a blossom. Unable to reach the nectar, mining and leaf-cutter bees, wasps, flower flies, and beetles visit it for the abundant pollen; and the common little white cabbage butterfly (Pieris protodice) sucks here constantly. The capsules of the sundrops are some-what club-shaped and four-winged, angled above, with four intervening ribs between. Range from Nova Scotia to Georgia, west beyond the Mississippi.

A similar, but smaller, diurraal species (K. pumilla), likewise found blooming in dry soil from June to August, has a more westerly range North and South.