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Friday, August 5, 2016

Sun Trackers

This time of year, the most notable family of plants are the Heilianthus, or sunflowers.  From the Greek ‘helios’ or sun and ‘anthos’ or flower, these plants are usually tall annuals or perennials that during their growth phase exhibit a subtle behavior in the daylight hours.  This behavior, called heliotropism, is the ability for the young flower buds and leaves to gently tilt toward the sun, tracking it as it moves across the sky. By the time the flower heads mature, they are stationary but generally facing east to greet the rising sun.

Sunflowers are typically tall plants with one to multiple flower heads, consisting of bright yellow ray florets or flowers, surrounding yellow or maroon disc florets.  In wild or native species, the rough and hairy stems are normally branched, and the leaves are often sticky and lance or heart-shaped. Sunflowers also exhibit phyllotaxis, or the arrangement of leaves on a stem that forms a distinct pattern, in this case a repeating spiral.  Additionally, the disc florets also display a phyllotactic pattern, one that creates the optical effect of criss-crossing spirals in the flower’s center.

Common Sunflower (Helianthus annuus)
In our area, the two most abundant sunflowers are the Common Sunflower (Helianthus annuus) and the Maximilian Sunflower (Helianthus maximiliani).  Blooming from May to October, the Common Sunflower grows on dry soils, especially in disturbed areas.  It can reach 1.5 to 8 feet tall, and various parts of the branched stems can be either green or dark purple.  The heart-shaped leaves are coarse and covered in rough hairs, and grow from 2.5 to 10 inches long.  Up to 4 inches across, the flower heads have yellow ray flowers and reddish brown disc flowers.  As their scientific name suggests, these plants are annuals.

Maximilian Sunflower (Helianthus maximiliani)
Maximilian Sunflowers, on the other hand, are perennials that bloom in September and October. They grow 1 to 6 feet tall in colonies on both the dry ground of prairies and the moist ground of roadside ditches and other low places.  Shorter, rough hairs cover the narrow lance-shaped leaves, which average 2 to 4 inches long.  The 1.5 to 3 inch wide flower heads have yellow ray flowers surrounding yellow disc flowers, with numerous flower heads growing along the unbranched stems.

Aside from their aesthetic value to humans, sunflowers are generally palatable to deer and numerous species of birds eat their seeds.  Their flower heads support nectaring bees, and they are the food plants for several butterfly species such as the Bordered Patch and Silvery Checkerspot.  When mixed with other native annuals, these sun trackers provide good cover for many species of wildlife, and would be a great addition to your native wildscape.