Virginia Tech Weed Identification Guide

Spanishneedles: Bidens bipinnata

Weed Description:  Summer annual with dissected leaves and yellow flowers reaching 5 1/2 feet in height.  Primarily a weed of pastures, roadsides, and noncrop areas that can be found throughout Virginia, Georgia, Florida, Alabama, Tennessee, Kentucky, and West Virginia. 

Seedling:  Stems below the cotyledons (hypocotyls) are maroon or slightly maroon-tinted and square.  Cotyledons green on the upper surface and maroon-tinted on the lower surface.  The upper surfaces of the cotyledons have a distinctive midvein.  First true leaves are opposite and deeply dissected.

Leaves: Opposite, with short hairs along the margins and veins that are pressed closely against the leaves (appressed).  Leaves are finely dissected and have 2 to 3 rows of lateral leaflets that are ovate to lanceolate in outline.

Stems:  Erect, square in cross-section, branching in the upper section, and with small tufts of hairs at the nodes.

Flowers:  Occur in solitary heads on long stalks.  Flowers are yellow and are composed of inner disk flowers and outer ray flowers.  Ray flowers are sometimes absent but are approximately 1/2 inch long and 3 mm wide.  Flowering heads are surrounded by green bracts that are approximately 2 to 7 mm long and narrow.

Fruit:  An achene that is approximately 8 to 18 mm long, linear in outline, and dark brown in color.  Achenes have 3 to 4 spines at the apex that are pointed downward.

Roots:  A taproot.

Identifying Characteristics:  Summer annual with leaves that are dissected 2 to 3 times and have yellow flowers.  Spanishneedles seedlings are similar in appearance to those of Common Ragweed (Ambrosia artemisiifolia), however the cotyledons of common ragweed are much more rounded than those of spanishneedles.  Additionally, common ragweed seedlings do not have the characteristic maroon highlights on the cotyledon and leaf undersurfaces like those of spanishneedles.  Devils Beggarticks (Bidens frondosa) is also similar in appearance to spanishneedles, however devils beggarticks does not have leaves that are dissected 2 to 3 times.  Spanishneedles can also be confused with Coreopsis Beggarticks (Bidens polylepis), however coreopsis beggarticks has flowers that are much larger and more showy and leaflets that are more linear than those of spanishneedles.