DESCRIPTION of INVASIVE HAWKWEEDS

Hawkweeds are fibrous-rooted, perennial herbs growing from a stout rhizome.  Plants reproduce by seeds and vegetatively by stolons, rhizomes, and adventitious root buds.  The small, dandelion-like heads are borne singly at the top of a long, hairy to hairless stem, or in compact, rounded or loose, elongated panicle-like clusters.  All but one invasive species has yellow flowers (likewise, all but one native species has yellow flowers).  Seed production is primarily asexual through apomixis (the production of seeds without pollen), although occasional sexual reproduction, outcrossing, and hybridization is believed to occur.  Hawkweeds are distinguished largely on a few key morphological characters, including leaf, stem and phyllary (involucral bract) pubescence.  Hairs, both type and abundance, are important characters used to distinguish hawkweed species.  Three types of hairs are common: long simple hairs; dark, glandular hairs; and small, star-shaped (stellate) hairs.  All invasive hawkweeds are polyploid (n=9) and typically asexual, compared to the entirely diploid and sexual native species.

Key to Identification of Invasive and Native Hawkweeds (Hieracium spp.) in the Pacific Northwest

Printable list of Invasive Hawkweeds (Word doc.)

Hawkweed Family Tree (Word doc.)