Bidens discoidea T. & G.) Britt.

Bidens discoidea plant

Family - Asteraceae

Stems - From fibrous roots, rooting at lower nodes, erect, 4-angled (the angles rounded), often purplish, glabrous or with a few antrorse hairs near the apex of the stem, delicate, much-branched, herbaceous, to 1.5m tall, single from the base.

Leaves - Opposite, petiolate, trifoliolate. Petioles to -5cm long, with narrow adaxial groove (the groove with sparse pubescence). Leaflets serrate, acuminate, glabrous or with a few antrorse hairs on the veins below, to 10cm long, 3cm broad, lanceolate. Serrations of margin often with minute whitish apices. Lateral leaflets with petiolules 1-3mm long. Terminal leaflet with a petiolule to +/-2cm long. Blade tissue of leaflets often obliquely terminating at the base.

Bidens discoidea leaves

Inflorescence - Loose cymose arrangement of flower heads terminating the branches.

Involucre - Outer phyllaries 1-5(6), to +3.5cm long, 5-6mm broad, entire, oblanceolate to spatulate or lanceolate, glabrous or occasionally with antrorse strigose margins, spreading. Inner bracts glabrous, green, erect, appressed, 5-6mm long, 2mm broad, blunt to subacute, often minutely fimbriate at apex (use a lens to see).

Bidens discoidea flowers

Ray flowers - Absent.

Disk flowers - Disk to 5-6mm broad in flower. Corolla +/-2mm long, whitish below, yellow at apex, 5-lobed, glabrous. Lobes erect to spreading, .2mm long, acute, yellow. Stamens 5, partially exserted, adnate in basal 1/3 of the corolla tube. Anthers purplish, connate around the style, .7mm long. Style exserted, bifurcate, yellow at the stigmas. Achenes to 5mm long, becoming greenish-black, 2-awned, compressed, antrorsely pubescent. Awns to 1.5mm long. Chaff translucent-green, orangish at apex, blunt, glabrous, to 6mm long, 1mm broad, linear.

Bidens discoidea flowers

Bidens discoidea flowers

Flowering - August - October.

Habitat - Wet ground.

Origin - Native to U.S.

Other info. - This species can be found mostly in the Ozark section of Missouri but also along rivers and swamps of a few more southern and central counties. The plant is fairly easy to ID in the field because of its small flower heads. Because it freely roots at the nodes, the plant can be found growing off the ground in dead stumps and from the bark of living trees.
The genus name "Bidens" means "two teeth" and is so given because of the two awns of the fruit.

Photographs taken in Brown Summit, NC., 9-8-02.


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