SHRUBBY BEARDTONGUES WITH WOOLLY ANTHERS (DASANTHERA
PENSTEMONS) By Myrna Jewett
beardtongues with woolly anthers are not unpleasant, bristly characters, but
are a group of western alpine flowers - memorable in the wild and good
choices for rock gardens. “Beardtongue” is the common name sometimes used
for Penstemon, a North American genus with about 270 species, mostly
inhabitants of western and plains states.
With close to 300 species, how does one figure out which ones to grow? Help comes from our own late, great plantsman, Roy Davidson. In his article “Penstemons of Value,” suggests woody penstemons, many native to the Northwest, for the rock garden. Woody penstemons include the Penstemon procerus alliance, a good choice if you are going for the blues. But he writes, “As nice as these species are, the most useful of the shrubby penstemons are those of subgenus Dasanthera, which includes about a dozen taxa, with forms varying from minute, matted plants to striking bushes one foot and 30 centimeters or more high, spreading to 3 ft./90 cm, or occasionally as much as 6 ft./180 cm.” The shrubby penstemons include evergreen, small-leaved, large-flowered plants, with blooms mostly in lavenders, violets and purples.
|Penstemon fruticosus, Wenatchee Mts., Washington|
|Coloradan Bob Nold, who has tried growing over 200 species of the 272
species he describes in his book on Penstemon, suggests penstemons for each
of traditional, Mediterranean, dry, rock and pot or trough gardens. For rock
gardens, “All Dasanthera penstemons are fabulous plants, along with their
cultivars and hybrids.” For container gardening, “Some of the smaller
Dasanthera penstemons make excellent trough plants”. I’m convinced!
The genus name Penstemon is now accepted as derived from “almost a thread (stamen)” rather than from “five stamens.” Penstemons have just four fertile stamens; the fifth is instead a staminode, with no pollen-producing anther. Its base is at the top back of the floral tube, but it drops down to the floor at the front. This staminode is bristly in some species; thus, beardtongue.
The subgenus name Dasanthera (see above note) is derived from the Greek dasy, thick or hairy, and anther; thus, stamens with woolly anthers, which key this subgroup. However, the utility of the hairy anther is not plainly understood.
There are nine species in Dasanthera,
some with further subdivisions. The species are: Penstemon
Of this group: P. ellipticus, P. lyallii and P. montanus are found in the Northern Rockies; the rest are found in the Cascade - Sierra Nevada mountains. P. fruticosus also inhabits intermountain regions. P. ellipticus and P. lyallii have woody bases only; the rest are more or less evergreen shrubs.
||Penstemon montanus, Western Wyoming|
||Penstemon rupicola, Cascade Mts. Washington|
||Penstemon davidsonii var. davidsonii, Crane Mt. Oregon|
including P. davidsonii and P. rupicola, are mat-forming, rooting at the
stems. Others are of clumping, carpeting or mounding habit. P. rupicola and
P. davidsonii inhabit rock crevices; the rest are often found in screes.
lyallii may exceed two feet in height; most are under 12” tall. Most have
purple or lavender blooms; P. newberryi and P. rupicola have red or magenta
All are insect pollinated, mostly by bees; P. newberryi and P. rupicola are also pollinated by humming-birds.
There are some nice books on penstemons, helpful for becoming acquainted with them in the wild, and also helpful for acquainting them to one’s garden. Dee Strickier’s book on Northwest penstemons describes 80 northwestern species, has good-sized photographs of each species, line drawings of distinguishing flower parts, and very approximate distribution maps for species and subspecies. Nold’s book, mentioned earlier, is an enthusiast’s dream come true, with descriptions of 272 species. Sixty-four are pictured in photographs, in reproductions of Cindy Nold’s watercolors, or in line drawings. This book contains a whole lot of information about the genus.
Penstemons were assigned to the figwort family, Scrophulariaceae, a large family with about 275 genera and 5000 species. Many members of this family have snapdragon-like, bilaterally symmetrical flowers.
But hold on to your hats! Taxonomists (botanists who like to classify plants and confuse/irritate horticulturists by renaming them), have a newish tool - DNA sequencing of plant genes - and they are stirring up the pot. Using computer analysis of DNA data, they are teasing out reasonable guesses of how present-day plants have evolved from common ancestors and how they are related to each other. They are redrawing the tree for flowering plants. So there goes the scroph family as it’s been known for about 150 years, and how we are used to seeing its members grouped together by family in plant identification books. Penstemons are newly placed in the Plantagenaceae, or the plantain family. Unfortunately precedence rules for nomenclature dictate the choice of family name. Thus Penstemon is in “Plantaginaceae”, and Mimulus is in “Phrymaceae” the lopseed family, and not “Mimulaceae”. Yuk!
These genetic studies indicate penstemons have a fairly recent and New World origin. The broad details of the story are: Penstemon putatively descended from Keckiella, a genus which today is found in the southwest and Baja California. Penstemons originated in ice age (Pleistocene) refugia in the northern Rocky Mountains. P. montanus, a Dasanthera now found in the Idaho to the Montana Rockies, may be our earliest extant penstemon, the parent of the rest of subgenus Dasanthera. This lineage migrated across the Columbia Plateau, then down the Cascade and Sierra Nevada mountains, shifting from suffrutescent (woody at the base) to more or less evergreen shrubs.
The nine Dasanthera species are the most ancient of the 270 or so penstemon species. Living at high elevations with short growing seasons, these are relatively long-lived and have a relatively long generation time. This results in a slower rate of genetic divergence, thus the Dasantheras hybridize readily with each other.
One more penstemon, P. personatus, may be included in subg. Dasanthera as a result of the genetic studies. P. personatus is a rare endemic to northern California, and previously was assigned to its own subgenus. Nold says of it: “a bizarre and not terribly attractive plant”. Hmmm.
P. montanus also may be parent to the rest of penstemon. Here, speciation occurred repeatedly, producing a twiggy branch of the family tree; a few penstemons eventually made it to the eastern US or as far south as Guatemala. New species arose rapidly as the genus expanded into new ecological niches and specialized for various pollinators.
Penstemons likely started out as bee-pollinated, but about 40 (15 percent) have shifted or are shifting from insect pollination to hummingbird pollination. This shift has occurred independently for various lineages of penstemons, as bird-pollination tends to be more efficient than bee-pollination. To see how this gradual shift might take place, envision an alpine habitat with a population of penstemons in bloom. The plants are not identical to each other, but vary in flower color, flower shape, etc. The hummingbirds, less sensitive to chilly temperatures than bees, show up earlier in the day than do nectaring and pollen-collecting bees.
|Sphinx Moth on Penstemon davidsonii var. davidsonii, Crane Mt. Oregon|
|Pollen grains are knocked off the
anthers of the flowers by the visitors, with some sticking to body surfaces.
The bees groom off the pollen grains; the hummers mostly ignore them. Some
stowaway grains are transported to other flowers, where they may be
dislodged. But, assuming an equal number of visits from birds and bees, more
pollen grains are successfully ferried from one flower to another by
hummers. So the genes (as pollen grains) hitchhiking with hummingbirds would
likely contain more alleles (alternate forms of genes) favorable to birds
than in the general population of plants, and those hitchhiking with bees
would tend to contain bee-friendly alleles. Because the birds are more
successful pollinators, the next generation will have a slight shift to
Some of the ways in which hummingbird flowers differ from insect pollinated flowers are: in color, the corollas are redder; in tube shape and length, the tubes are narrower and longer; in the lower lip shape, it forms a less-pronounced or absent insect-landing platform; in the orientation of the floral tubes the pedicels are more inclined, making the flowers easier for hummers to approach; in the placement of stigma and anthers, the anthers are exserted (outside the tube) rather than inserted; in pollen release, pollen is released less frequently, but in larger quantities; in nectar:, nectar is less-concentrated, but produced in greater quantities.
We know why bees visit blue/purple flowers before red: they can see blue flowers better than they can see red flowers, so it takes them longer to find the red flowers. But why hummingbirds visit red flowers is more of a mystery as they see the colors blue and red equally well. The blue! purple, or bee-pollinated penstemons, are seldom visited by hummers (but are visited by other insects), while the red, or bird-pollinated penstemons, including P. rupicola and P. newberryi, are visited by both bees and birds.
By the way, does anyone grow the magenta and white forms of P. rupicola side-by-side and have they observed any difference in visits by hummers to the two color forms?
Northwest chapter members have a long history of seeking out and selecting forms of Dasantheras. I’ve found references to selections and hybrids introduced by early Northwestern chapter member Carl English, by Roy Davidson, and by present chapter members Carla Lankow and Rick Lupp. Mark McDonnough, who lived in this area for a while, has introduced several hybrids.
Penstemons are available from mail-order nurseries; Dasantheras are included in the on-line catalogs of: Mt. Tahoma Nursery, Beaver Creek Greenhouses, Fraser’s Thimble Farms, Pacific Rim Native Plant Nursery and Siskiyou Rare Plant Nursery. Other sources for penstemons are local nurseries specializing in natives, NARGS plants sales, or, best of all, fellow chapter members sharing seedlings and rooted cuttings from their gardens (thank you!).
Seeds are available from commercial seed collectors and from seed exchanges, including that of the American Penstemon Society. This group was founded in 1945, showing great dedication of some to the genus.
So which penstemons to grow? Any or all of the Dasantheras. Include the red ones, to see if the hummers will come. Now that I have narrowed down a group of penstemons to grow, have even learned something about their history, and know something about their habitat - alpine, thus stony, sunny and cool - my next question is how will they fare with me? And, will I become a...
B. LeRoy Davidson, Penstemons of Value, pp 126 -132, in Rock Garden Plants of North America, 1996, Jane McGary, editor
Dale Lindgren and Ellen Wilde, Growing Penstemons: species, cultivars and hybrids, 2003
Robert Nold, Penstemons, 1999
Dee Strickler, Northwest Penstemons, 1997
Note: For the complete bibliography, which includes about a dozen journal articles about DNA and pollination studies, published since 2000, please contact Myrna.