JAMES A. YOUNG AND RAYMOND A. EVANS Highlight: Germination tests on squirreltail seed showed that three temperature regimes always produced optimum germination of 76 to 100%. We defined optimum as not statistically (p = 0.01) different from maximum. The always optimum temperature regimes were: (1) a constant 15?C, (2) alternating 10/15?C (16 hours cold/8 hours warm each day), and (3) 10/20?C. When seed was produced in a year with good growing conditions, optimum germination extended over a wide range of temperatures. At optimum temperatures, the rate of germination was very rapid with a high percentage of total germination occurring within a week. The lack of inherent germination requirements that restrict germination, high germinability, and a rapid rate of germination help to explain the colonizing ability of this species.