Variations on a Theme: Sunflowers


woodland sunflower
Helianthus divaricatus



thin-leaved sunflower
Helianthus decapetalus

These two species have very similar looking inflorescences, with yellow disks and anywhere from 8 to 20 rays; note that despite the specific epithet “decapetalus” (meaning ten petals), thin-leaved sunflower does not always have ten rays.

Both grow from two to six feet tall. Despite this and the similar flowers, it’s easy to tell them apart if you look at some of the details.

Habitat: woodland sunflower, as the name suggests, tends to be found in the shade of woodlands, often in drier soils than the other species.  Thin-leaved sunflower is more often found in open areas between trails and the river, where there’s more sun and moisture.


Woodland sunflower has long-tapering, lance-shaped leaves  that are either sessile or with very short petioles. The margins have a few slight teeth. The leaf surface is rough to the touch, like sandpaper.


The leaves of thin-leaved sunflower have long petioles, often winged (especially the larger leaves, which are sharply toothed), and the top leaf surface is smooth.

Woodland sunflower can be found in the eastern US and a few states west of the Mississippi.  In the Potomac Gorge, it’s not too common.  It’s listed as “special concern” in Rhode Island.

Thin-leaved sunflower has a similar range and is much easier to find in the Gorge, especially along the eastern half of Billy Goat C.  There are no conservation issues.

Sixty more native species and naturally occurring hybrids of Helianthus are in the continental US and Canada. Seventeen total can be found in Maryland; of these, three are listed as S1 (“highly state rare”) by the DNR.

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Flowers of the Day: Sunflowers

woodland sunflower, Helianthus divaricatus 

thin-leaved sunflower, Helianthus decapetalus

Asteraceae (aster family)


Both of these woodland species share a similar range across the eastern US. The woodland sunflower likes conditions a little shadier and a little drier, while thin-leaved sunflower likes a bit more sun and moisture.  Woodland sunflower will grow three to six feet tall, with flowers one and a half to three inches across.  Thin-leaved sunflower will grow to five feet tall and can have slightly larger flowers (two to three and a half inches across).

(both images above: woodland sunflower; below: thin-leaved sunflower)

The most obvious differences between the two lie in the leaves. Woodland sunflower leaves are blunt at the base, sessile (the leaf base touches the stem of the plant), and are exceptionally long-pointed at the tip.  Thin-leaved sunflower has a slightly long-tipped leaf that narrows dramatically into long, winged petioles.