Helianthus annuus  L. 1753

pronounced: hee-lee-AN-thuss AN-oo-uss

(Asteraceae —  the daisy family)

common name: Common Sunflower, Sunflower

helianthus annuuswild sunflower helianthus annuusstand of sunflowersHelianthus is from two Greek words, 'ηλιος (helios), the sun, and ανθος (anthos), a flower; annuus is a Latin word that means ‘that lasts a year’, i.e., is an annual plant. In warm climates, the plants tend to be perennial, especially when they have encroached into the wild. The sunflower is native to the Americas, and was probably first domesticated in Mexico by at least 2600 BC.

What is usually called the flower is actually a composite flower, of numerous florets crowded together. The outer florets are the sterile ray florets, usually yellow, and the inner ones disk florets, that mature into ‘sunflower seeds’, the fruit of the plant. The inedible husk is the wall of the fruit, and the true seed lies within.

The florets within the sunflower’s cluster are arranged in a spiraling pattern, where the number of left spirals and the number of right spirals are successive Fibonacci numbers. Typically there are 34 spirals in one direction and 55 in the other, though there are often more in the larger flowers of the domestic sunflower.

helianthus annuusdomestic sunflowers helianthus annuusdomestic sunflower In the bud stage sunflowers exhibit heliotropism – at sunrise the flowers are turned towards the east. During the day, they follow the sun’s course and end up facing west, returning to their eastward-facing position during the night. As the bud stage ends, the stem stiffens, usually leaving the flowers facing east. Typically, the wild sunflower does not turn towards the sun: its flowering heads may face many directions when mature, but its leaves usually exhibit some heliotropism.

Many indigenous American peoples, including the Aztecs and the Otomi of Mexico, and the Incas of South America, used the sunflower as the symbol of the sun god. Gold images of the flowers, as well as sunflower seeds, were taken back to Spain early in the 16th century.

fruit On Magnetic Island there are quite a few stands of these wild sunflowers by road verges. They may have started as garden escapees. The ones photographed are situated in Picnic Street, Picnic Bay, near where the road crosses Butler’s Creek. When in flower they make a brave show.

The caterpillars of several Lepidoptera species feed on sunflowers. These include:

• the Tomato Grub Helicoverpa armigera;
• the Soybean Looper Thysanoplusia orichalcea;
• the Yellow Peach Moth Conogethes punctiferalis;
• the Light Ermine Moth Spilosoma canescens;
• the Australian Native Budworm Helicoverpa punctigera;
• the Apple Looper Phrissogonus laticostata;
• the Cotton Web Spinner Achyra affinitalis; and
• the Tobacco Looper Chrysodeixis argentifera.

Photographs taken in Picnic Bay 2008, 2009

Page last updated 19th March 2018

 

 

 

 

 

 

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