Oenothera linifolia Nutt. - Threadleaf Evening Primrose

Oenothera linifolia plant

Family - Onograceae

Stems - To +/-30cm tall, erect, herbaceous, simple to branching near apex, from a branched taproot, multiple from base, hirsutulous below, glabrous near apex.

Leaves - Alternate. Basal rosette typically drying by anthesis. Leaves of rosette petiolate, spatulate, to 3cm long, 6mm broad, entire to shallow serrate, glabrous. Cauline leaves linear, 2-3cm long, 1-2mm broad, glabrous, entire.

Oenothera linifolia leaves

Inflorescence - Terminal raceme, compact in flower, elongating in fruit. Each flower subtended by a single bract. Bracts acute to acuminate, lance-ovate, mostly glabrous, entire but with strigose margins. Flowers sessile.

Oenothera linifolia infloresence

Flowers - Petals 4, yellow, distinct, obcordate, 5mm long, 4-5mm broad, glabrous. Stamens 8, erect, adnate at apex of floral tube. Filaments yellow, glabrous, +/-2mm long. Anthers reddish-yellow, .7mm long. Style yellowish, glabrous, 4.5mm long. Stigma 4(5)-lobed. Ovary inferior, 4-locular, 4-angled, slightly winged on angles, obovoid in outline, 5-6mm long n flower, longer in fruit, with antrorse strigose pubescence. Placentation axile. Ovules many. Floral tube yellow, 3mm long, mostly glabrous or with a few strigose hairs as ovary. Sepals 2, reflexed, ovate, glabrous internally, with small strigose hairs externally, yellow-green, -3mm long, 2.3mm broad.

Oenothera linifolia flowerFlower close-up.

Oenothera linifolia calyxCalyx close-up.

Oenothera linifolia fruitFruit close-up.

Flowering - April - July.

Habitat - Glades, rocky fields.

Origin - Native to U.S.

Other info. - This small species can be found in the southern half of Missouri. The small flowers of this species wilt quickly and barely last a day. More commonly, the plant is found in fruit, if at all. Because of its thin stems and leaves, and its small flowers, this species is often overlooked.
This is a characteristic glade species in Missouri.

Photographs taken at Dave Rock Conservation Area, St. Clair County, MO., 6-16-05, and on Taum Sauk Mountain, MO., 6-1-03.


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