Taxonomy

Bidens biternata (Lour.) Merr. & Sherff, The Botanical Gazette 88: 293. 1829.

Common synonyms

Coreopsis biternata Lour. Fl. Cochinch. 2: 508. 1790; Actinea biternata (Lour.) Spreng.; Bidens abyssinica Sch.Bip.

Common name

Yellow-flowered blackjack

Description

Propagule or dispersal unit is the fruit with pappus. Fertile part 6-15 mm long, 0.4-1 mm wide, in side view mostly +/- equal thickness (cylindrical), widest in the middle, rarely widest in upper part (obovoid) (by misinterpretation), conspicuously curved, the upper (apical) end narrowing or suddenly cut off (truncate), in cross-section angular (prismatic), basal scar (carpopodium) pronounced and well-differentiated, off to the side (oblique) or at least asymmetric, beak (=thinner sterile stalk between seed and pappus) absent, wings absent, fruit surface black, smooth (except at cellular level), with no hairs (glabrous) or simple straight hairs, thickened margin absent, longitudinal ribs present, 5-10, their surfaces smooth or bumpy or notched (by misinterpretation), with no hairs (glabrous) or simple straight hairs.

Pappus type awns or spines, pappus elements all +/- similar or clearly differentiated, up to 1.5-4.5 mm long, in one row, number of pappus elements three to four, persistent, the individual awns serrated or barbed, +/- divergent, +/- straight.

Notes: This species has three to four pappus awns, and the fourth may be smaller than the others. The surface appears to have a surface ornamentation under the microscope, but this is merely the cell network. Nonetheless, the species has been scored to accommodate a user who checks it as having a bumpy surface. Ribs can be counted as either five with regular surface between them, or as ten. Among the three Bidens in this key that have non-flattened fruits this species stands out through its consistently hairless fruit surfaces.