Date of this Version
University of Nebraska Studies : new series no. 39, March 1969
The genus Carduus L., a member of the Compositae, consists of approximately 120 species native to Europe (Arenes, 1949; Mulligan and Frankton, 1954). Of these, C. acanthoides L., C. crispus L. and C. nutans L., have been introduced to North America, but only C. acanthoides and C. nutans have been reported in Nebraska.
A general description of the Nebraska members of this genus is as follows: annuals or biennials; herbaceous stems spiny winged; leaves lobed with spiny margins; heads solitary or clustered at end of branches; phyllaries imbricated, spine-tipped in many rows; florets tubular, perfect, usually purple, rarely white; cypsela oblong, glabrous, with shallow longitudinal grooves; pappus of simple, denticulate hairs in many rows.
From field observations, it appeared that the seeds of Carduus normally germinate in mid-summer and then the plant passes through the following winter in a rosette stage. In the spring the plant mayor may not bolt and produce flowers. If it does not bolt, then it passes through the next winter still in the rosette stage.
According to present evidence, members of the genus Carduus were introduced into Nebraska in the early 1930's, but they posed no significant problem until recently. However, since approximately 1958, the population has demonstrated a dramatically rapid increase from a few scattered members in the southeast portion of the state to large stands covering up to twenty or more acres. This increase has become so great that in 1966, upon the recommendation of the Nebraska Extension Weed Control, the genus was placed on the Nebraska list of noxious weeds.