CARDUUS CINEREUS (ASTERACEAE) – NEW TO NORTH AMERICA

Abstract

Carduus cinereus M.Bieb. populations have been discovered in the Hells Canyon Wilderness of northeastern Oregon and western Idaho. These plants were initially identified as C. pycnocephalus L. They are distinguished from that species by loosely clustered, usually pedunculate, heads and by scarious-margined phyllaries. These plants are genetically distant from other North American Carduus species (<94% similarity) based on DNA sequence comparisons of the internal transcribed spacers between the 18S and 26S nuclear rDNA regions. Carduus cinereus is new to North America. A revised key to the species of Carduus in North America is presented.