1	"Anther sacs not dehiscing full length (opening only partly)"	2
1	"Anther sacs dehiscing full length, valves generally spreading widely apart"	3
2	"Anther sacs dehiscing at distal end (proximal portion indehiscent) (subg. <i>Habroanthus</i>)"	"Penstemon Group 1"
2	"Anther sacs dehiscing at proximal end (leaving distal portion indehiscent) (subg. <i>Saccanthera</i>)"	"Penstemon Group 2"
3	"Corolla mouth closed by arched floor (subg. <i>Cryptostemon</i>)"	"Penstemon personatus"
3	"Corolla mouth open"	4
4	"Anthers densely woolly (subg. <i>Dasanthera</i>)"	"Penstemon Group 3"
4	"Anthers glabrous (subg. <i>Penstemon</i>)"	"Penstemon Group 4"