Type for Wiborgia oblongifolia Hook. Catalog Number: US 1803415 Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany Verification Degree: Original publication and alleged type specimen examined Preparation: Pressed specimen Collector(s): A. Cruickshanks Locality: Lurin, near Lima., Lima, Peru, South America
Yerba de Tajo is a common plant in southern and central Illinois, but uncommon or absent in northern Illinois, where it may be adventive (see Distribution Map). This plant has a world-wide distribution and can be found in many Pacific Islands. It is a common weed in the American tropics, but in some of the northern states in the U.S., such as Wisconsin and New York, it is considered an endangered or threatened native plant. In Illinois, habitats include poorly drained areas of moist black soil prairies, muddy borders of ponds and rivers, ditches, poorly drained areas in fields, gardens and edges of yards. This plant is most often found in disturbed wetland habitats, but it occasionally occurs in areas that are drier and more developed.
Annual herb, usually with prostrate or decumbent stems, rooting at the nodes, sometimes suberect. Leaves subsessile, elliptic-lanceolate, up to 12 × 2.5 cm; margins toothed. Capitula solitary in the upper leaf axils, 6-10 mm in diameter. Ray-florets, 1-2 seriate, short, numerous, white.