Aster family (Asteraceae)
Description: This adventive plant is a winter or summer annual about 4-12" tall that occasionally forms side stems in the upper half. The round stems often have fine veins or longitudinal ridges, and they are hollow on the inside. Toward the base of the plant, the stems are often purplish green. The alternate leaves are up to 4" long and ¾" across. They are usually odd pinnate and have a few blunt teeth along the margins in addition to the lobes. The terminal lobes are often truncated or notched, rather than pointed. The edges of the leaf margins curve downward (revolute). The lower leaves have short stout petioles, while the upper leaves are sessile or clasp the stems. Some of the uppermost leaves may be lanceolate or oblong and smaller in size. The hairiness of the stems and leaves is highly variable, ranging from nearly glabrous to densely covered with white hairs that are appressed and cobwebby in appearance.
The upper stems terminate in small dense clusters of composite flowers. Each composite flower is more or less cylindrical in shape, spanning about ¼" in diameter and ½" in length. Its apex is densely crowded with tiny yellow disk florets; there are no ray florets. Each disk floret has 5 slender lobes that curl backward when it is in bloom. The inner floral bracts are arranged in a row around the cylinder as a single series. They are slender and green, sometimes with black upper tips. There are also outer floral bracts that are shorter and spread outward from the base of the flowerhead. They are also slender and green, except that their upper tips are always black. The blooming period for a population of plants can occur from early spring to late fall. An individual plant remains in bloom for about 3-4 weeks. Each disk floret is replaced by a slender achene with a tuft of white hair, which facilitates distribution by wind. The surface of these achenes is finely pubescent and can become sticky when wet. The root system consists of a shallow taproot. This plant spreads by reseeding itself.
Cultivation: Common Groundsel is often found in full or partial sun, mesic conditions, and fertile loamy soil. It blooms in as little as 5 weeks after the seeds germinate, and appears to favor cooler weather during the spring or fall.
Range & Habitat: In areas where it occurs, Common Groundsel is often locally common, otherwise it is uncommon or absent. In Illinois, Common Groundsel occurs primarily in NE Illinois and a few counties in central Illinois (see Distribution Map). Because this plant is rather inconspicuous, it is possible that official records underestimate its actual distribution within the state. Habitats include lawns, gardens, edges of yards, nursery plots, areas along railroads, and miscellaneous waste areas. It prefers highly disturbed areas where the vegetation is low or scant. Common Groundsel is native to Eurasia.
Faunal Associations: The tiny florets occasionally attract flower flies and small bees. Insects that feed on this grounsel include the leaf beetle Longitarsus jacobaeae, the polyphagous aphid Macrosiphum gei, and caterpillars of the moth Orthonama obstipata (The Gem). This plant is not a significant source of food for mammalian herbivores because the foliage and flowers contain a toxic alkaloid that can damage the liver. The value to wildlife of this species is rather low.
Photographic Location: At the edge of a lawn near the webmaster's apartment complex in Urbana, Illinois.
Comments: This is an inconspicuous little plant that is easily overlooked. There is another introduced Senecio sp. with a similar appearance. This species is Senecio viscosus (Sticky Groundsel), which has foul-smelling foliage that is covered with sticky glandular hairs. Unlike Common Groundsel, the floral bracts of this species never have black upper tips. While Common Groundsel often has hairs, they are non-glandular and the foliage isn't foul-smelling. Some authorities assert that Common Groundsel is always without hairs, but this isn't true.