Evening Primrose

Oenothera stricta Ledeb. ex Link

Synonyms - Oenothera odorata, Oenothera striata.

Family: Onagraceae.

Names:

Evening Primrose because its flowers open in the evening.

Other names:

Common Evening Primrose.

Summary:

Evening Primrose is an erect herb with a basal rosette of long, narrow leaves and a leafy spike with showy flowers. The flowers are up to 80 mm across and yellow, opening in the evening, becoming tinged with red and withering the following day. The flowers are up to 10 cm across with a slender tube, 4 large spreading petals and 8 stamens. The fruit is long and slender. The stem is up to 1 m tall and lacks the prominent red spots present on some other species. It has a tuberous rootstock.
Native to South America, it is a common roadside weed and flowers for much of the year with a flush in spring.

Description:

Cotyledons:

Two. Oval. Pimply or frosted surface. Tip round. Base tapered. Edges slightly toothed. Hairless. Short petiole.

First leaves:

Narrowly oval, Tip pointed. Edges slightly toothed. Base tapered. Short petiole. Hairless.

Leaves:

Spirally arranged, alternate. Basal leaves form a rosette.
Stipules - none.
Petiole - leaf narrowed into a petiole-like base.
Blade - Dark green, parallel sided to lance shaped, 80-260 mm long x 5-10 mm wide. Midrib conspicuous and often pale or white. Usually has tiny teeth near the tip. Tip pointed, Sides toothed or smooth and convex. Base tapering. Usually hairless.
Stem leaves - Become shorter up the stem, 30-100 mm long x 5-12 mm wide, almost no petiole to half-clasping, wavy edges, sharp teeth near the tips. Usually with tiny hairs.

Stems:

Stiff, erect or bending upwards, 500-1000 mm tall, glandular, often whitish and tinged with red, occasionally becoming woody. Unbranched or just a few branches. Hairy, especially near the top. Short blunt hairs mixed with long hairs that don't have a bulbous base.

Flower head:

Single stalkless flowers in axils of leafy bracts on erect long stems.
Long leafy spike.

Flowers:

Yellow to orange fading to purple. They open early in the morning or late in the afternoon and wither by the next day as the flower above it opens. Fragrant, tubular, erect.
Ovary - 10-12 mm long, 4 celled, silky and glandular hairs. Style 10-15 mm long with 4 spreading stigma lobes 3-8 mm long. Receptacle tube 20-40 mm long.
Sepals - 4, Green to reddish, 15-20 mm long x 1.5-2.5 mm wide, and lance shaped, bent outwards. Hairy. Tips often joined in pairs.
Petals - 4, 22-40 mm long, egg shaped, notched, overlapping, spreading, yellow or orange then turn red-purple. Tubular or on the top of the slender receptacle tube.
Stamens - In 2 rings of 4. Filaments 12-15 mm long.
Anthers - 6-8 mm long, versatile, attached on the back. Pollen in sets of 4 cells.
Free part of receptacle tube falls off with the sepals with age.

Fruit:

Capsule, 18-35 mm long, club shaped, broadest in the upper most third, silky (long) and glandular (short) hairs. Splits into 4 sections along its midribs from the top downward to release the seed and leaving the persistent axis.

Seeds:

Yellow to brown. Almost smooth, egg shaped to oval to tear shaped, 1 mm long x 0.75 mm wide. Tip round to pointed. Edges smooth to rough. Base round to pointed. Surface rough and dull. No tuft of hairs.

Roots:

Fleshy rootstock.

Key Characters:

Leaves almost entire. Capsule ribbed and broadest in the upper most third. Flowers yellow turning red when they wither. Receptacle 30-35 mm long or less. Long hairs on the stem don't have a bulbous base. Hairy sepals. Has glandular hairs on the stem.

Biology:

Life cycle:

Annual, biennial or perennial. Grows throughout the year depending on available moisture and growth may be slow in the cooler months. Flowers October to November and rarely in autumn. Seeds germinate from autumn to spring.

Physiology:

Reproduction:

By seed and rootstock.

Flowering times:

Most of the year in SA.
Mainly from September to March in western NSW.

Seed Biology and Germination:

Vegetative Propagules:

Fleshy rootstock.

Hybrids:

Forms hybrids with closely related species.

Allelopathy:

Population Dynamics and Dispersal:

Spread by intentional planting and seed.

Origin and History:

South America. Chile.

Distribution:

ACT, NSW, NT, QLD, SA, TAS, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Mainly on sandy soils.

Climate:

Most abundant in coastal locations.

Soil:

Sandy soils.

Plant Associations:

Significance:

Beneficial:

Ornamental.
Fodder.
Soil stabiliser for sandy areas prone to wind erosion.
Honey plant.
Does not host Root Lesion Nematode (Pratylenchus neglectus or thornei) (63).

Detrimental:

Weed of roadsides and disturbed areas.

Toxicity:

Not recorded as toxic.

Legislation:

None.

Management and Control:

Increased grazing pressure or cultivation normally controls it.

Thresholds:

Eradication strategies:

It is difficult to remove by hand because it tends to break off and regrow from the rootstock. If removing manually, use a fork and ensure that all the fleshy rootstock is collected and burnt or buried more than 1 m deep.
It is relatively tolerant of glyphosate.
Spray young actively growing plants and a 5 m buffer area in spring or autumn with 50 g/ha Logran® plus 1% spray oil. Use 1 g Logran® plus 100 mL spray oil in 10 L water for hand spraying. Alternatively 4 L/ha 2,4-DB(400g/L) may be used. Both herbicides are relatively selective in bushland situations. 2,4-DB is preferred in areas where there are many seedlings of native species.
Respray regrowth as it appears.
2,4-D amine(500g/L) at 1-3 L/ha is used in South Australia for control in pastures.

Herbicide resistance:

Biological Control:

Related plants:

Beach Evening Primrose (Oenothera drummondii) is hairier, has larger leaves and capsules and is usually close to the sea.
Common Evening Primrose (Oenothera stricta) is a herb to 1 m high, with narrower leaves and stems lacking prominent red spots. The flowers are smaller and up to 8 cm across. Common on roadsides.
Four winged Evening Primrose (Oenothera tetraptera)
Long flowered Evening Primrose (Oenothera affinis) has longer leaves, slightly larger flowers and is hairier.
Rose Evening Primrose (Oenothera rosea)
Small flowered Evening Primrose (Oenothera indecora) has smaller flowers.
Tall Evening Primrose (Oenothera glazioviana) is a herb to 1.5 m high with stems that have tiny red spots (the bases of hairs). The flowers are larger and up to 10 cm across and occur from early summer to autumn. Common on roadsides.
White Evening Primrose (Oenothera speciosa) has pinnately lobed lower leaves and white or pink flowers.
(Oenothera acaulis)
(Oenothera glazioviana)
(Oenothera laciniata) is a low sprawling plant.
(Oenothera molissima) is often on limestone soils.

Plants of similar appearance:

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P193. Photo.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P638. Diagram.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P277-278. Diagram.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P534. Photo.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P188. Photo.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #893.9.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P433.

Moerkerk, M.R. and Barnett, A.G. (1998). More Crop Weeds. R.G. and F.J. Richardson, Melbourne. P109. Diagrams. Photos.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.