Se. Meyer et Sg. Kitchen, HABITAT-CORRELATED VARIATION IN SEED-GERMINATION RESPONSE TO CHILLINGIN PENSTEMON SECTION GLABRI (SCROPHULARIACEAE), The American midland naturalist, 132(2), 1994, pp. 349-365
Members of Penstemon Section Glabri are common perennial herbs in habi
tats from desert shrublands to subalpine meadows throughout the Interm
ountain West. Germination response to moist chilling was evaluated for
36 populations belonging to 13 species within the section. Eleven spe
cies (P. cyananthus, P. cyaneus, P. cyanocaulis, P. fremontii, P. laev
is, P. leiophyllus, P. perpulcher, P. scariosus, P. speciosus, P. stri
ctus and P. subglaber) had seeds that were largely dormant at harvest
and responded positively to chilling, whereas two (P. ammophilus and P
. commarhenus) had seeds that were largely nondormant. The proportion
of seeds that could be rendered nondormant through chilling varied amo
ng species, populations and years of collection; many middle elevation
collections contained a large fraction nonresponsive to chill. Most c
hill-responsive seeds germinated during prolonged chilling. Across spe
cies, germination rate during chilling was significantly correlated wi
th mean January temperature at the collection site for each of 3 yr of
collection, i.e., collections from habitats with warmer winters germi
nated more quickly in the cold than those from sites with colder winte
rs. Similarly, the chilling period needed for maximal postchilling ger
mination increased as collection site winter temperature decreased. Ex
periments with common garden-grown seeds of six of the species showed
that patterns characteristic of wild-collected seeds persisted in the
garden, indicating a probable genetic basis for the differences. Adapt
ive radiation in Penstemon Section Glabri has resulted in evolution of
population-level germination syndromes that maximize the probability
of establishment in a range of specific habitats.