Small Sundrops
Oenothera perennis
Evening Primrose family (Onagraceae)

Description: This perennial wildflower is 8-24" long, unbranched or sparingly branched, and erect to ascending. The stems are light green to pale red and terete; they are often pubescent above, becoming glabrous below. The alternate leaves are up to 2" long and " across; they are medium green, glabrous to slightly pubescent, and narrowly ovate or elliptic. The base of each leaf is sessile, while its tip is blunt. In addition to the alternate leaves, the basal leaves are often present at the bottom of each plant. The central stem (and any lateral stems) terminates in a leafy spike of several flowers; it is usually several inches long. Individual flowers usually alternate along the spike, although sometimes they occur in pairs. At the base of each flower, there is a leafy bract about –1" long that is linear-oblong. The central stalk of the spike is often pubescent.

Each flower is about –" across, consisting of 4 yellow petals, 4 green or reddish green calyx lobes, a slender calyx tube that is often reddish, and an ovary that is located below the calyx tube. There are also several yellow stamens and a central style with a cross-shaped stigma. The well-rounded petals are often slightly notched at their tips. Each petal has a central vein, from which several lateral veins radiate from both sides; these veins are pale-colored and rather inconspicuous. The calyx lobes are lanceolate in the shape and pubescent on their outer surfaces; they eventually hang downward from the petals and turn yellow. The calyx tube is about the same length or a little shorter than the ovary. The blooming period occurs from early to mid-summer and lasts about a month; the flowers are diurnal. After the blooming period, each fertile flower is replaced by a pubescent seed capsule about " long; it is ovoid-obovoid with 4 strongly winged margins along its sides that are reddish green. Each capsule contains numerous seeds.

Cultivation: The preference is full or partial sun, moist to dry-mesic conditions, and sandy or gravelly soil.

Range & Habitat: Small Sundrops is a boreal species that is restricted to NE Illinois, where it is native. This plant is rare in Illinois and state-listed as 'endangered.' Habitats include sand prairies, gravel prairies, sandy savannas and open woodlands, and abandoned sandy fields. In some parts of its range, this wildflower is found in damp depressions of various kinds. Occasional wildfires and brush-removal are beneficial because they reduce competition from woody vegetation.

Faunal Associations: The flowers are cross-pollinated by bees, skippers, and butterflies; a Halictid bee, Lasioglossum oenotherae, is an oligolege (specialist pollinator) of Oenothera spp. These insects suck nectar from the flowers, and some bees also collect pollen for their larvae. There are several insects that feed on Oenothera spp. They include the caterpillars of Eudryas unio (Pearly Wood Nymph), Schinia florida (Primrose Moth), and some Mompha spp. (Momphid Moths). Other insect feeders include the weevils Tyloderma foveolatum and Chalcodermus collaris, and the aphid Anoecia oenotherae. The seeds of Oenothera spp. are eaten to a minor extent by the Eastern Goldfinch and Mourning Dove, while the foliage is sometimes eaten by White-Tailed Deer.

Photographic Location: A nature preserve in Cook County, Illinois. The photograph was taken by Lisa Culp (Copyright 2009).

Comments: Small Sundrops is a pretty little plant that blooms during the day. It resembles the often cultivated Oenothera fruticosa (Common Sundrops), but this latter plant has larger flowers (1" across or more) that bloom together in rather flat-topped clusters. In contrast, the flowers of Small Sundrops bloom along a more elongated floral spike. Other Oenothera spp. have seed capsules that lack the strongly winged margins that are characteristic of Small Sundrops' seed capsules. Some Oenothera spp. have night-blooming flowers that are pollinated by Sphinx moths; they are commonly referred to as 'Evening Primroses' rather than Sundrops.