Sunflower

Helianthus annuus L.

Family: Asteraceae.

Names:

Helianthus is from the Greek helios for sun and anthos for flower because the flower heads turn towards the sun.
Annuus refers to its annual growth form.
Sunflower refers to its flowers that look like and follow the sun.

Other names:

Annual Sunflower.
Common Sunflower.

Summary:

A coarsely hairy, stout, rough to touch, erect stemmed annual or occasionally biennial plant to 3000 mm tall with large leaves and large yellow flowers with a black centre.

Description:

Cotyledons:

Two. Large, oval. Tip pointed. Base tapering. No stalk.

First leaves:

Dull green, oval, rough to touch. Short hairs. Strong Sunflower odour when crushed.

Leaves:

Mainly alternate but sometimes opposite on the lower stem. Rough hairs.
Stipules - None.
Petiole - Long.
Blade - Dark green on upper and lower surfaces, egg shaped to triangular, 10-200 mm long x 60-120 mm wide, 3 prominent veins. Base may be notched where the petiole joins almost at right angles to the blade. Edges usually serrated. Tip tapering to a point. Stiff, low lying hairs on both surfaces.

Stems:

Erect, stout, up to 3000 mm tall. Usually single but may branch from the upper leaf axils or from the base. Coarsely hairy.

Flower head:

Bright yellow with a dark centre, single, nodding on a long stalk (peduncle) at the end of stems. Small headed and giant headed varieties. Head of naturalised plants usually about 50-100 mm wide and cultivated varieties may have heads up to 300 mm diameter.

Flowers:

Large with yellow petals surrounding a brown-black centre. Black centres of flowers of cultivated forms up to 300 mm diameter and wild forms up to 100 mm diameter.
Bracts - In several overlapping rows underneath head are egg shaped to oblong, more than 4 mm long quickly tapering to the tip, or 3 lobed and membranous and roughly to silky hairy.
Florets - Ray florets without stamens or ovary (neuter), bright yellow usually in one row with oval to oblong ligules, 20-40 mm long that fall off as head matures.
Disc florets, bisexual, tubular, brownish to purplish black, many, 5 lobed. Finely hairy on the lower swollen part of the tube.
Ovary - Receptacle is slightly convex, with 3 lobed membranous scales that are as long as the floret. Style branches are lance shaped and flattened with stiff red collecting hairs on the back and sides of the branches.
'Petals' - Yellow, 20-40 mm long, fall off as flower matures.
Stamens -
Anthers -

Fruit:

Achene about 5 mm long, wedge shaped, flattened, 4 angled, smooth to very finely hairy, brown or black often with white or grey stripes. Pappus of scales that fall off easily.

Seeds:

Black, dull, often with white or grey stripes. Oval to tear shaped, 10-12 mm long x 5-6 mm wide by 2-4 mm thick. Surface smooth, ridged and hairy.

Roots:

Strong taproot.

Key Characters:

Leaves mainly alternate. Disc florets with red, purple or brown lobes. Involucre bracts usually more than 4 mm wide, ovate to narrowly ovate and often abruptly attenuate. Disc usually more than 30 mm diameter. Achene glabrous.
Large yellow daisy-like flowers with a dark centre.

Biology:

Life cycle:

Annual or occasionally biennial. Germination mainly occurs in the warmer months but it will germinate at any time of the year and grow then flower whenever moisture is available. Flowering mainly occurs from February to September.

Physiology:

Reproduction:

Flowering times:

Summer in SA.
Mainly summer with occasional flowers throughout the year in western NSW.
February to May in Perth.
February to September in WA.

Seed Biology and Germination:

Vegetative Propagules:

None.

Hybrids:

There are a number of commercial varieties and hybrids.

Allelopathy:

Population Dynamics and Dispersal:

Spreads slowly.

Origin and History:

North America.

Distribution:

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

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Warm temperate.

Soil:

On moist soil types. Often more common on sandy soils.

Plant Associations:

Significance:

Beneficial:

Commercially grown for fodder, birdseed, and oil from its seed.
Buds are used as a cooked vegetable.
Seeds are eaten raw or roasted or ground into a coffee beverage.
Honey plant.

Detrimental:

Weed of roadsides, disturbed areas and fallows.
Not grazed to any extent by stock, but birds eat the seed.

Toxicity:

Pollen may cause asthma.
May cause allergic dermatitis.

Legislation:

None.

Management and Control:

Thresholds:

Eradication strategies:

Herbicide resistance:

Biological Control:

Related plants:

Texas Blueweed (Helianthus ciliaris)
Jerusalem Artichoke (Helianthus tuberosus).
Helianthus debilis is a more slender plant with reddish stems

Plants of similar appearance:

Crown Beard (Verbesina encelioides) is similar but has expanded wings at the base of the leaf stalk, opposite leaves on the lower stem and smaller flower heads.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P104. Photo.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P876.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P679-680. 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). P98. 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). #632.1.

Moerkerk, M.R. and Barnett, A.G. (1998). More Crop Weeds. R.G. and F.J. Richardson, Melbourne. P59. Diagrams. Photos.

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). P682.

Acknowledgments:

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