1.Two Competing Hypotheses Relating to Thermostress Were Proposed to Understand Skewed Sex Ratios in Syntrichia Caninervis, a Reproductive Investment Hypothesis and a Wildfire Selection Hypothesis.2.Nearly All Shoots from Both Sexes Remained Viable (Regenerated in Culture) Following Exposure to 120 °C for 30 Min, Thus Setting a New Upper Thermotolerance Record for Adult Eukaryotic Organisms for a Minimum 30 Min Exposure Time.3.Males Regenerated Faster Than Females, Produced More Biomass, and Suffered Less Fungal Attack Than Females. Findings Support the Wildfire Selection Hypothesis. © 2008 Elsevier Ltd.