Does smoke promote seed germination in 10 Interior West Penstemon species?

Recent research has shown that exposing seeds to smoke stimulates germination for a multitude of plant species, including several species in the genus Penstemon (Scrophulariaceae). I evaluated whether smoke, either alone or followed by 10 wk of stratification (moist prechilling), influenced germination for 10 Penstemon species native to the Interior West of North America. Seeds were collected from 3 to 9 wild populations per species, with each population serving as a replicate for that species in the experimental design. I found that percent germination increased in response to smoke for 3 species, Penstemon secundiflorus Benth., P. strictus Benth., and P. unilateralis Rydb., with smoke-exposed seeds exhibiting 1.9-, 2.5-, and 1.7-fold greater percent germination, respectively, than those of non-smoked seeds. Increased germination in P. unilateralis was only observed for seeds that had also been stratified, while increased germination for P. secundiflorus and P. strictus was observed for both stratified and non-stratified seeds. I also found that percent germination was stimulated by stratification for 6 species, P. auriberbis Pennell, P. eriantherus Pursh, P. glaber Pursh, P. rydbergii A. Nelson, P. secundiflorus, and P. strictus. Penstemon auriberbis, P. eriantherus, and P. secundiflorus were the most responsive, with percent germination increasing 63.4-, 10.6-, and 9.7-fold, respectively, following stratification. These findings improve our understanding of the role of smoke, as well as the role of stratification, in Penstemon germination ecology and should be of use to those who wish to propagate Penstemon species for restoration, horticultural, research, and other purposes.