|Penstemon oklahomensis is a member of Penstemon subg. Penstemon sect. Penstemon subsect. Penstemon (Bennett et al. 1987). Its common name is Oklahoma Beardtongue, and it is one of just a few plants found only in Oklahoma. Penstemon oklahomensis is also unusual in having a closed throat, which limits nectar access to large bumblebees. Carpenter bees and honeybees access the nectaries through slits at the base of the corolla, and are nectar thieves.|
Bennett, R. W., K. Lodewick, and R. Lodewick. 1987. Penstemon nomenclature. Eugene, OR: American Penstemon Society.
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