A new invasive hawkweed, <i>Hieracium glomeratum</i> (Lactuceae, Asteraceae), in the Pacific Northwest

Abstract

During the summer of 2001, a newly recorded species of exotic hawkweed ( Hieracium glomeratum Froel.) for North America was identified from specimens collected in southeastern British Columbia, Canada, and eastern Washington state, United States. The specimens had previously been identified as the closely related Hieracium caespitosum Dumort. DNA fingerprints of plants from different localities proved to be identical. Their clonality, along with a spot-like distribution, indicates that this apomictic species probably originated from a single introduction from Europe, which subsequently spread. This species adds to the complex of 14 other exotic Hieracium species belonging to the Eurasian subgenus Pilosella that are adventive in the United States and Canada. A distribution map of the native and adventive range of H. glomeratum, and a key to distinguish it from related species in subgenus Pilosella that occur in North America are provided. The evolutionary and invasive potential of H. glomeratum is also discussed.