Description

O. biennis has been described in varying detail by Gleason and Cronquist (Reference Gleason and Cronquist1991), Zomlefer (Reference Zomlefer1994), Miller and Miller (Reference Miller and Miller1999), Bryson and DeFelice (Reference Bryson and DeFelice2010), and Wagner (Reference Wagner2017); the following summary is derived from these sources. Common evening-primrose is an erect biennial that can grow to heights of 2 m. A deep, fleshy, fibrous taproot anchors the plant in the ground. Seeds germinate in the summer or fall and give rise to rosette leaves that are 5- to 30-cm long and 1- to 7-cm wide. Rosette leaves are alternate, with long petioles and blades that are lanceolate, pubescent, and have tips that are gradually pointed. Leaf margins are entire to sometimes shallowly dentate or wavy. Cauline leaves are up to 15-cm long and 4-cm wide, alternate, lanceolate, pinnately veined, and are sessile or else held on short petioles. Stems produced the second year are erect, stout, and branched with short, appressed trichomes often giving them a reddish appearance. Plant tissues contain raphides (i.e., bundles of needle-like calcium oxalate crystals) and tannins.

Oenothera flowers occur in a terminal spike that can be 0.6 m or more long. Mature buds are erect and curve upward. Flowers are regular, perfect, and sessile in the leaf axils. The corolla has four obovate petals that are yellow fading to pale reddish and 1.0- to 2.5-cm long. Floral tubes are 2- to 5-cm long, slender greenish-yellow, pubescent, with glandular or plain trichomes. Stamens as long or longer than the stigma and style. There are four greenish-yellow sepals that are reflexed at anthesis. An interesting attribute of the Onagraceae is their distinctive pollen characteristics. Pollen grains may occur in tetrads or monads, are relatively large, and are more or less triangular due to three protruding, stopper-like apertures. Pollen grains are connected with viscin threads, which are composed of an elastic and somewhat viscid material. Viscin threads may vary in number and structure. These slender strands also occur on pollen of certain Ericaceae.

Darlington and Steinbauer (Reference Darlington and Steinbauer1961), Gleason and Cronquist (Reference Gleason and Cronquist1991), Zomlefer (Reference Zomlefer1994), Miller and Miller (Reference Miller and Miller1999), and Bryson and DeFelice (Reference Bryson and DeFelice2010) have all described the fruiting structures and senescence of common evening-primrose in some detail. Fruits are a capsule that is 1.4- to 3.5-cm long and 3.5- to 6-mm thick near the base, strigose to subglabrous, four-celled, four-angled, and many-seeded. Capsules gradually split from the tip downward to the base, progressively releasing the seeds. Seeds occur in two rows in each locule. Seeds are 1.3- to 1.6-mm long, sharply angled, irregularly shaped, pyramidal with a varying number of sides, reddish-brown, ridged, and often have winged edges. Because they have no special adaptations for dispersal, most seeds are released close to the parent plant. Seeds may remain viable in the soil for decades (Darlington and Steinbauer Reference Darlington and Steinbauer1961). Although the parent plants die after setting seeds, the erect and leafless stems often persist into winter (Bryson and DeFelice Reference Bryson and DeFelice2010; Miller and Miller Reference Miller and Miller1999; Gleason and Cronquist Reference Gleason and Cronquist1991; Zomlefer Reference Zomlefer1994).

In the southern United States, common evening-primrose plants will typically flower from June to October. The attractive and scented yellow flowers typically open at dusk (hence the name “evening primrose”) in synchrony with the nocturnal feeding habits of primary pollinators (especially Hymenoptera and Lepidoptera) (Horn and Cathcart Reference Horn and Cathcart2005; Mabberley Reference Mabberly1997; Zomlefer Reference Zomlefer1994). Flowers remain open until morning and potentially longer on cloudy days. Nectar is secreted at the base of the style or by nectaries within the lower part of the hypanthium and accumulates in the floral tube. The pollen sticks to insects by means of the viscin strands that form between the pollen grains. Cross-pollination is generally promoted by protandry, although self-pollination is prevalent in this family as well (Zomlefer Reference Zomlefer1994). Reproduction is by seeds, which may be dispersed by wind and birds.

History and Distribution

Pollen from the Onagraceae “appears in generalized form in the Maastrichtian, and in gradually increasing diversity form the Eocene onwards” (Gleason and Cronquist Reference Gleason and Cronquist1991). The genus Oenothera may have spread from Central to North America between the successive ice ages of the Pleistocene epoch. The prolific genetic diveristy of this genus may be due, in part, to hybridization between survivors of different colonizing events. Common evening-primrose is now endemic to much of North America, ranging from Mexico to Florida; north to central Ontario and Quebec, Canada; and west to North Dakota and Oklahoma. It can also be found along the Pacific coastline of North America (WSSA 2019).

From its origins in North America, O. biennis has been moved by man and become established in all other continents, excluding Antarctica. Its first documented introduction to Europe was in 1870 in England; it was imported for its medicinal qualities. From there it became well established through much of Western Europe. During the 1960s, there was a measurable increase in the area invaded by common evening-primrose, which was characterized by spread into central and eastern Europe. Interestingly, the proliferation of Oenothera spp. in Europe has actually occurred because of the influx of two distinct groups of this genus. The biennial species of common evening-primrose, which originated from North America, is reported to be well adapted to inland conditions in Europe (which has lower mean temperatures and more balanced monthly precipitation) as compared with annual and perennial Oenothera spp. originating from South America, which favor a more oceanic climate. Common evening-primrose has also spread to Japan, Australia, and South Africa, and has become established, or is becoming established, in most other temperate environments around the globe (Frean et al. Reference Frean, Balkwell, Gold and Burt1997; Holm et al. Reference Holm, Pancho, Herberger and Plucknett1991; Mihulka and Pysek Reference Mihulka and Pysek2001; Miller and Miller Reference Miller and Miller1999; Stadler et al. Reference Stadler, Mungai and Brand1998).

The literature on the Onagraceae, especially the genus Oenothera (e.g., Cleland Reference Cleland1972), is extensive, with many studies focused on embryology, cytology, chemistry, and evolutionary ecology; O. biennis was one of the earliest model species in genetics and cytogenetics. (Conti et al. Reference Conti, Faschback and Sytsma1993; Johnson Reference Johnson2011). According to Johnson (Reference Johnson2011) O. glaziovana Micheli, in Martius, which is a hybrid of O. biennis and O. elata subsp. Hoookeri, played a role in the rediscovery of Mendel’s laws of inheritance through the independent assortment of alleles. This is despite that many Oenothera (at least 43 species), including common evening-primrose, do not display independent assortment, owing to permanent translocation heterozygosity. With permanent translocation heterozygosity, progeny are genetically identical to their parent plant, because of a lack of recombination and segregation.

Characteristics

Uses

Many indigenous peoples in North America used Oenothera spp. generally (and common evening-primrose, in particular) for food and medicinal purposes (Borchers et al. Reference Borchers, Keen, Stern and Gershwin2000; Moerman Reference Moerman1998). For example, the Cherokee cooked and ate common evening-primrose leaves as greens and boiled the roots like potatoes (Hamel and Chiltoskey Reference Hamel and Chiltoskey1975; Perry Reference Perry1975). Seeds had several uses. Members of the Gosiute used them for food, and the Lakota are reported to have burned them as incense. The Potawatomi used the tiny seeds as a medicine for unspecified ailments (Chamberlin Reference Chamberlin1911; Rogers Reference Rogers1980; Smith Reference Smith1932a). The Ojibwa tribe soaked the whole plant and applied it to bruises (Smith Reference Smith1932b). The Iroquois, Cherokee, Ojibwa, and Potawatomi peoples used O. biennis to varying degrees as a dermatological aid, a hemorrhoid remedy, a treatment for premenstrual and menstrual pains, and a stimulant and strengthener (Borchers et al. Reference Borchers, Keen, Stern and Gershwin2000; Hamel and Chiltoskey Reference Hamel and Chiltoskey1975; Herrick Reference Herrick1977).

Culpeper’s Complete Herbal stated the primroses were a commonly used remedy and the leaves could be made into a salve to heal wounds (Culpeper Reference Culpeper1653). Common evening-primrose extracts inhibit Escherichia coli and Staphylococcus spp. (Hayes Reference Hayes1947). Seeds are a source of γ-linoleic acid, important in production of fatty acids and prostaglandins and used in the treatment of premenstrual tension (Mabberley Reference Mabberly1997). The seed oil has been investigated experimentally for treating a wide variety of conditions, including eczema, asthma, inflammation, premenstrual syndrome, breast problems, metabolic disorders, arthritis, and alcoholism (Coffee Reference Coffey1993). Common evening-primrose is a source of a pain-relieving compound used for headaches and a remedy for venereal disease and eruptions of the skin (Horn and Cathcart Reference Horn and Cathcart2005). Complementing the aforementioned indigenous knowledge, there is documentation that, during the first year of growth, the young roots may be boiled and eaten as a vegetable and the shoots, fruits, and seeds may be consumed (Coffee Reference Coffey1993; Horn and Cathcart Reference Horn and Cathcart2005; Mabberley Reference Mabberly1997).

Common evening-primrose has nutritional value for wildlife, such as various small mammals, as well as white-tailed deer. Birds, including the northern bobwhite, mourning dove, American goldfinch, and dark-eyed junco, consume the seed (Kindscher Reference Kindscher1987, Mabberly Reference Mabberly1997; Miller and Miller Reference Miller and Miller1999; Stubbendieck et al. Reference Stubbendieck, Friisoe and Bolick1994). The flowers are nectar sources for many moths and butterflies, particularly sphinx moths (Hilty Reference Hilty2018; Miller and Miller Reference Miller and Miller1999). Several species of bees, including honeybees and bumble bees, have been reported to visit common evening-primrose flowers seeking nectar and/or pollen (Hilty Reference Hilty2018). In addition, the larvae of some moths and beetles consume O. biennis plant parts. Numerous species of aphids and adult beetles feed on the foliage, including adult Japanese beetles (Popillia japonica Newman) (Hilty Reference Hilty2018).