Bidens frondosa L.

Global description

Bidens frondosa is an upright annual herbaceous plant, branched, with opposite, simple leaves, but deeply lobed to the point of appearing to be composed of 3 or 5 narrowly oval lobes, with a strongly toothed margin. The base of the lateral lobes is narrowed into an acute wedge forming a pseudo-petiole. The inflorescence is made up of numerous terminal or subterminal capitula, pedunculated, surrounded by an involucre of 2 series of bracts. The outer bracts are foliaceous and distinctly longer than the inner ones. The peripheral ligulate florets are very few (0 to 3), yellow in colour, the central tubular florets are numerous and orange. The fruit is a very flattened achene, topped with two strong straight spines, with more or less warty with short, stiff hairs.

General habit

Bidens frondosa is an upright, abundantly branched or even bushy annual plant, 20 to 120 (200) cm high.

Stem

The stem is cylindrical, solid, finely cannaliculate and often tinged with red. It is glabrous or subglabrous.

Leaf

The leaves are opposite, borne on a 10 to 40 (60) mm  long. The blade is simple but deeply lobed, with 3 to 5 fully individual lobes, leaving the rachis (midvein) bare. The general shape of the leaf blade is broadly ovate to ovate lanceolate, 3 to 8 (15) cm long and 2 to 6 (10) cm wide. The lobes (resembling leaflets) are narrowly oval, 2 to 6 (12) cm long and 1 to 2 (3) cm wide. The base is acute wedge-shaped, often asymmetrical and more or less attenuated into a pseudo-petiole, the apex is long acuminate and the margin is strongly toothed. The secondary and tertiary veins are pinnate. Both sides are glabrous or very finely pubescent.

Inflorescence

The inflorescence consists of a very large number of terminal and axillary flower heads at the level of the terminal leaves, borne on 10 to 40 (80) mm long peduncles. The flower head is campanulate or hemispherical, 6 to 9 mm long and 7 to 12 mm in diameter. It is surrounded by an involucre with 2 series of bracts. The outer bracts (5 to 10) are erect or more or less spread out, spatulate or oblanceolate, sometimes even foliate, and much larger than the inner bracts. They are 5 to 20 (60) mm long and 3 to 6 mm wide. They are glabrous or finely pubescent on the underside. The inner bracts (6 to 12) are lanceolate, erect, 5 to 9 mm long, not extending beyond the  florets.

Flower

The peripheral ray florets are few (1 to 3) or usually absent, 2 to 3.5 mm long and yellow in colour. The central tubular florets (20 to 60 (100)) are 2.5 to 3 mm long and yellow-orange in colour.

Fruit

The fruit is a flattened achene, obovate or broadly wedge-shaped, dark brown to black in colour. The smaller outer achenes are 5 to 7 mm long, while the larger inner achenes are 7 to 10 mm long and 3 to 4 mm wide. They are topped by two strong, straight, erect lateral spines, 2 to 5 mm long. The faces and spines are more or less warty and covered with short, stiff hairs.

Origin

Bidens frondosa is native to North America.

Worldwide distribution

This species has been introduced to Morocco, Western Europe, Central Europe, Asia (China) and New Zealand.

https://www.gbif.org/species/5392174