The photo above shows naked-stemmed evening-primrose as seen along the Domingo Pass Road in the Pueblo Mts of southeastern Oregon.........5/27/2000.
Naked-stemmed evening-primrose is an annual wildflower with a cluster of basal leaves and erect to spreading stems up to 40 cm long. The stems of smaller plants are usually simple while those of larger plants is often branched with the central stem erect while the side stems may be prostrate to ascending.
The herbage of the leaves is mostly glabrous although the stems may be glandular or variously haired, including densely fine haired or covered with longer, stiff and sharp appressed hairs. The leaves are petiolate with the blade ovate to lance-ovate or elliptic in shape and measuring up to 6 cm long and up to 3 cm wide. The margins may be entire or toothed and small lateral lobes or segments maybe found below the large terminal blade. The main veins on the undersides of the blades maybe lined with oil-cells.
The numerous flowers are in elongating racemes with the unopened buds clustered at the nodding tip of the stem. The floral tube ranges from 1.1-4.5 mm long. The 4 sepals are 2-4 mm long, separate and reflexed downwards when in bloom. The yellow petals are 2-5 mm long and may contain fine red spots near the base of the petals. The 8 stamens have anthers from 0.5-2 mm long. The style is roughly equal in length to the stamens, and the globose stigma is closely surrounded by the anthers. The fruit is a thick, cylindrical capsule from 1.2-4 cm long and 2-3 mm thick. The capsules are roughly 0.4-4 times longer than the pedicels which spread or ascend.
Subspecies brachycarpa: Paiute Suncup
Subspecies scapoidea: Leaves simple with entire margins. Oil-cells lining the veins on the undersides of the leaf blades pale yellowish-brown, rarely darker. Found from eastern Oregon east through Idaho to southwestern Montana and south through eastern Nevada, Utah, western Wyoming and Colorado to northern Arizona and northwestern New Mexico. Paiute Suncup
Subspecies utahensis: Leaves more or less dentate and often pinnately compound. Oil-cells lining the veins on the undersides of the leaf blades dark brownish. Found from southeastern Oregon east through southwestern Idaho and south through northeastern Nevada to western Utah. Utah Suncup
Naked-stemmed evening-primrose may be found in open areas in the desert on sandy, gravelly or clay soils from 700-1900 meters of elevation.
Naked-stemmed evening-primrose may be found from southeastern Oregon south to eastern Nevada, Utah, western Wyoming, Colorado and south to northern Arizona and northwestern New Mexico. It is found eastward through Idaho and southwestern Montana. The species may also be found in southeastern Washington.