Helianthus divaricatus L. - Woodland Sunflower

Helianthus divaricatus plant

Family - Asteraceae

Stems - Thin erect, simple, herbaceous, typically single from the base, from a long horizontal rhizome, typically purplish and somewhat glaucous, mostly glabrous but with a few pustulate based hairs directly below the nodes, terete, 2-4mm in diameter at the base, -1m tall, with +/-10 nodes below the flowers.

Helianthus divaricatus rootRoot.

Helianthus divaricatus stem

Leaves - Opposite, decussate, sessile or very-short petiolate. Petioles to 2mm long. Blades lanceolate, attenuate, shallow serrate, very scabrous on the top, less scabrous below, rounded at the base, the lowest to +10cm long, +/-2cm broad at the base, with two lateral veins arising from the base of the blade. Teeth of the margins often with a minute white tip.

Helianthus divaricatus leaves

Helianthus divaricatus leaf baseLeaf base.

Helianthus divaricatus leaf adaxialAdaxial surface of leaf.

Helianthus divaricatus leaf abaxialAbaxial surface of leaf.

Inflorescence - Single terminal flower head, typically just one per stem.

Involucre - -2cm broad in flower, 2.5cm broad in fruit. Phyllaries lanceolate, scabrous externally, glabrous internally, acuminate, to 1cm long and 5mm broad at the base, spreading with the tips ascending, light green, with ciliolate margins, imbricate.

Helianthus divaricatus involucre

Ray flowers - 8-9 flower per head, sterile. Ligule yellow, oblong, 2.5-3cm long, to 1cm broad, glabrous, acute with a very small single notch at the apex. Corolla tube -1mm long, glabrous. Achenes (in flower) -3mm long. Pappus of ray flowers a pair of serrate awns to 2mm long.

Helianthus divaricatus flowers

Disk flowers - Disk 1-1.5cm broad in flower, up to 2cm long in fruit. Flowers yellow. Corolla tube 3-4mm long, yellow, mostly glabrous but with some antrorse strigose pubescence externally (mostly in lines), glabrous internally, abruptly contracted at the basal 1mm. Lobes 5, 1-1.3mm long in flower, acute, erect to spreading. Stamens 5, included, adnate at the apex of the constricted portion of the corolla tube. Filaments white glabrous , 3mm long. Anthers maroon 3mm long, connate around the style, mostly included. Style exserted , glabrous, white, bifurcate, +/-5mm long. Stigmas yellow, to +2mm long, pubescent, reflexed. Achenes (in flower) white, glabrous, 3-4mm long. Pappus of 2 awns as in the ray flowers. Awns 2-3mm long. Receptacle hemispheric. Chaff enclosing the disk flowers almost entirely, to -1cm long, glabrous in basal half, pubescent on the margins and apex, slightly yellowish at the apex, acute, with a slightly reddish tip.

Helianthus divaricatus disk

Flowering - July - October.

Habitat - Rocky woods and thickets.

Origin - Native to U.S.

Other info. - This species can be found in the eastern-most counties of Missouri (essentially in the counties bordering the Mississippi River). The plant can be identified by its opposite, scabrous, sessile to nearly sessile leaves (which have rounded bases), thin stems, and long rhizomes.

Photographs taken at Fort Benning, GA., 7-3-05.


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