펜스테몬 우닐라테랄리스-[정명] Penstemon unilateralis Rydb.

One of the most familiar and beloved wildflowers in the Rocky Mountains is the so-called “one-sided penstemon”.  True to its name, the plant has its flowers all on one side of the stem. 

You can read the Wikipedia article about this plant.

Recently it crossed my mind that I had no idea why the plant goes to the trouble of keeping all of its flowers on one side of the step.  So I surfed around a bit on the Internet.  I figured that surely this must be a question that has occurred to others!  Surely there must be web sites at which this question has been raised, thoroughly discussed, and answered fully.

But no.  So far as I can tell, nobody has ever thought this to be a question worth raising.  So far as I can tell, the question has never been the topic of discussion.  I am not aware of anyone having answered this question.

Family:Plantain (Plantaginaceae)
AKA: Oneside Beardtongue
Photo taken on: July 18, 2016
Location: CO SR 114, S of Cochetopa Pass
Life Zones: Foothills to montane
Habitat: Shady slopes, roadsides

Grows to 2 feet with flowers on one side of the stem. Leaves are long narrow and folded inwards. Flowers are broad with a white throat and strong purple lines, nectar guides. The stamens are white, curved and hairless. The sterile stamen is white, hairless, broader at the tip and extends a little from the throat. This differentiates it from some of the similarly patterned Beardtongues.

Flora of North America reference.

https://youtu.be/FGsgB9eyuJU