Native to the western United States. There are several dozen species of native plants in this genus, many of which are rare and some of which are classified as Protected or Threatened species.
Perennial plants with foliage that dies back in the winter, with new growth from the rootstock in the spring. Reproduction is from wind blown seeds. Plants usually require habitats with high moisture, and often are highly localized in their distribution due to their occurrence in temporary pools of water. Sometimes will be found as a common roadside plant.
Plants have a bushy appearance due to the numerous and dividing stems, which are slender and fairly weak, and generally without leaves. Small leaves occur basally. Stems and leaves may be covered with a dense layer of minute, soft hairs. The extremely spiny flower heads appear at the ends and junctions of stems, without any showy petals.
Characteristicts Important to Control:
While these plants may grow along roadside and in disturbed fields, their presence is not considered noxious, and with the protected status of some species they should not be controlled until positively identified.