The Beardtongues?

Here is a genus that I find interesting. The Penstemon is made up of approximately 270 species and is the largest genus of flowering plants that are endemic to North America. Now classified in the plantain family (Plantaginaceae), this is a very diverse genus found across a variety of habitats and altitudes. Most species should be readily identified as a Penstemon due to their unique flower morphology. The corolla is a fused tube, comprised of five petals that can be identified as lobes in a two on top, three on the bottom configuration. Inside the corolla you will find two pairs of stamens with anthers pushed towards the top of the open mouth. In between the fertile stamens is a staminode that lies towards the bottom of the tube. This sterile modified stamen usually ends in a brush-like structure. This is the eponymous “beardtongue”. The generic name, Penstemon, meaning “stamen-like”, also refers to this staminode.

I got to meet four species of Penstemon in bloom this year – two of which I planted in the garden. I was happy to see them bloom in their first season.

Penstemon pallidus (pale penstemon) from my front garden in St. Louis Co., MO.
A closeup of Penstemon pallidus flowers. Note the yellow beard (staminode) that is thought to aid in pollination by pushing hymenopteran pollinators towards the stigma and anthers located at the top of the corolla tube. Also note the dark nectar guides that point towards the back of the tube.
Penstemon digitalis (foxglove beardtongue) is the most common and least particular member of the genus in eastern Missouri. These plants were found in a field at Beckemeier Conservation Area in St. Louis County.
The flowers of Penstemon digitalis are mostly white in color and have a relatively long blooming period compared to other local members of the genus.
Penstemon tubaeflorus is a showy white penstemon that is found primarily in the southwestern quadrant in Missouri. These photos were taken at Tingler Prairie Natural Area near West Plains, MO.
Here you can see why this species gets its common name of ‘trumpet beardtongue.’
The large and showy flowers of Penstemon cobaea (prairie beardtongue). These were photographed from the author’s front garden in St. Louis Co., MO.
I used focus stacking to capture the details in the flower of this Penstemon cobaea (prairie beardtongue). Note the two pairs of stamens that wrap around the inside of the corolla and present their pollen-filled anthers at the top. The stiff brush-like beard of the staminode pushes would-be pollinators towards these reproductive organs.

-OZB

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