Dodecatheon hendersonii

Shooting stars (April 4^th)

Dodecatheon hendersonii A.Gray (syn. Primula hendersonii A.R.Mast & Reveal), or Henderson's shooting stars, was extremely floriferous this spring. Vast swaths of the woodland countryside were filled with the mauve to violet (occasionally white) inverted flowers. This article is an attempt to give the reader an introduction to their morphology, life cycle, ecology (including pollination ecology), nomenclature, and my own personal observations in a relatively simple prose. It is my wish that the reader will become swooned by this plant. For me, knowing the intimate details of how a particular species "works" and interacts with the life around it helps me gain a deep admiration for that species. After all, flowers aren't necessarily for our eyes, but serve a greater purpose. Please enjoy!

Dodecatheon hendersonii (April 4^th)

Dodecatheon is a member of the family Primulaceae, and shares many similar characteristics with the genus Primula. Recent phylogenetic evidence even goes so far as to suggest that Dodecatheon is monophyletic and evolved from within the genus Primula, specifically subgenus Auriculastrum. To explain this in better detail, it is useful to know a bit about the genus Primula: Primula has a cosmopolitan distribution, while Dodecatheon is a mostly New World genus with the exception of one species (D. frigidum) which has a disjunct range that extends from Western Canada and Alaska into Eastern Russia, having apparently migrated across the Bering Strait. Primula is largely heterostylous, meaning there are two floral morphs: pin and thrum. The thrum morph has filaments that hold the anthers out with a reduced stigma that remains concealed in the calyx. With the pin morph, the configuration is reversed. Most Primula need cross-pollination between both morphs to set seed, although there is evidence that seed can occasionally be produced with two of the same morph. It is believed that Dodecatheon evolved from a pin morph due to the protruding stigma.

Primula veris (left) & P. vulgaris (right), both pin morphs from Primula section Primula, both share characteristics with Dodecatheon including form and color.

The name Dodecatheon appears to have been first used to refer to a Primula on Mt. Olympus by the Roman naturalist Gaius Plinius Secundus (AD 23-79), more familiarly known as Pliny the Elder. The name Dodecatheon is Greek meaning "twelve" (dōdeka, δώδεκα) "gods" (theoi, θεοί) in reference to the twelve primary gods in Greek mythology who resided atop Mt. Olympus. Theories as to why this name was given to a Primula vary considerably, but the most reasonable in my opinion is that the flower was so beloved to Pliny that he was sure that the flowers were protected by the gods, divine. Of course, Pliny would have never encountered the genus Dodecatheon as we now know it in Greece (or Rome), however, Mt. Olympus is host to a few primulas. Primula vulgaris subsp. rubra (Sm.) Arcang. (synonymous with Primula vulgaris subsp. sibthorpii (Hoffmanns.) W.W.Sm. & Forrest and perhaps Primula altaica, commonly referenced as part of the Olympian flora in older literature) as well as Primula veris are part of the modern Olympian flora.

Dissected flower of Dodecatheon hendersonii, from top: sepals, ovary (hidden), stigma; perianth; androecium

Fast forward to the year 1753, and Carl Linnaeus publishes Species Plantarum, a botanical reference work and one of the first (if not the first) to apply binomial nomenclature (genus, species). On the study and review of countless botanical samples from around the world, including the relatively new Virginia Colony, he received a sample of what we now know as Dodecatheon meadia. For a long time, the genus appears to have been considered monotypic.

Pollinator guides on the perianth; anthers with rugose connectives in the foreground.

By the year 1886, Asa Gray, a now famed and celebrated botanist from the 19th century, had authored Essay Toward a Revision of Dodecatheon in the Botanical Gazette (Vol. 11, No. 9 (Sep., 1886), pp. 231-234) describing five species of Dodecatheon where only one D. meadia, was previously considered. This is also where D. hendersonii first appears. This species, native from Northern California, through Western Oregon and Washington, and into Southwestern British Columbia, was first collected by famed plant collector Louis Henderson who suspected this was not D. meadia when he sent the sample to Asa Gray. The epithet hendersonii was given by Asa Gray to honor the collector.

Anthers are poricidal in newly opened flowers (requiring sonication for pollen dispersal).

It is difficult to talk about nomenclature and not talk about pollination ecology, since in this case the things which differentiate Dodecatheon from Primula are the things that specialize Dodecatheon for its pollination syndrome (sonication or buzz-pollination provided by bumblebees, Anthophorine bees, and possibly Eucerine bees). Dodecatheon is monomorphic (having one floral form, unlike most species of Primula) yet is specialized for sonication, or buzz-pollination. Swept back petals on pendant flowers strongly correlate with bee-pollinated plants. The anthers, though not fused, are tightly oriented against the stigma, which protrudes slightly. 

Stigma and part of androecium removed to show pollen within androecium.

The anthers open on the inside of the cluster yielding yellow/cream colored pollen which must be sonicated to be obtained. Rugose anther connectives (and sometimes filaments) in some species, including D. hendersonii, offer sonicating pollinators a foothold while on species where the anther connectives are smooth sonicating bees have been observed to slip off. Another comparison, Primula produces nectar as the main reward for pollinators while Dodecatheon, however, has abandoned nectar production in favor of enlarged anthers and the production of excess pollen, an alternative pollinator reward. The lack of nectar helped Dodecatheon curb visits from ineffective pollinators (flies, beetles, Lepidoptera) and instead gave greater rewards to their most efficient pollinators: bees.

Leaves and buds of D. hendersonii in late February, not too dissimilar from some Primula at this stage of growth.

Plants are ephemeral, leaves appearing in late winter, flowering in spring, then quickly setting seed and disappearing. They survive dormancy as a fleshy starfish-like crown (see a photo of a crown here courtesy of Mary Sue Ittner from the Pacific Bulb Society Wiki). The crown is very fragile during dormancy, and the ground is also very hard at this stage so digging would surely damage or kill the plants. Growth initiates again sometime after the first fall rains. Some combination of moisture and temperature are ideal for flowering, and this year we has a lot of rain and a swift raise in daily temperature which compressed the flowering period for Dodecatheon. Most years the flowering is stretched over many weeks, some individuals flowering and setting seed before others even open their buds.

Seed pods (April 19^th)

When flowers are pollinated, they turn up to face the sky. The ovary swells to become a capsule where the seeds are developed. As the capsules dry, the "lid" (what's left of the anthers, stigma, and petals) will fall off leaving a cup. The seeds are dispersed mechanically by act of wind shaking the then dry scape where the seeds will simply be flung out or they will just pour out.

D. hendersonii growing around the base of a stand of Arctostaphylos viscida (April 4^th)

Dodecatheon hendersonii grows in woodland clearings and forest edges, often where it can get some sun but without the overwhelming competition of an open field. Associations include Arbutus menziesii, Arctostaphylos viscida, Ceanothus sp., Erythronium hendersonii, Pinus ponderosa, and a variety of others. Many of the plants that it grows with associate with mycorrhizal fungi, and D. hendersonii was found to form larger roots when inoculated with arbuscular mycorrhizal fungi. Primula is also known to form endomycorrhizal associations, though neither Dodecatheon nor Primula appear to require it.

A white flowered individual in the center (April 4^th)

While many species of Primula have self-incompatibility safeguards in place (seeds produced from self-sown plants do not germinate), Dodecatheon is fully self-compatible. However, not all of the flowers on a given specimen will have receptive stigma or pollen available at the same time, encouraging bees to visit multiple plants, over a period of days or weeks, to collect the pollen as it becomes available.

An uncommon white form of Dodecatheon hendersonii (April 4^th)

Apparently rare white forms weren't uncommon this year, likely due to the sheer magnitude of this year's bloom. Interesting that they should lack the red pigmentation not just in the flowers themselves, but also the scape which is typically a reddish hue.

An uncommon white form of Dodecatheon hendersonii (April 4^th)

An aging white-flowered Dodecatheon hendersonii. Note that as the flowers age, the anthers are no longer poricidal.

A somewhat intermediate colored form, this aging flower had the reddish scape and pedicels and a purplish blush on the mostly white petals. As the flowers of D. hendersonii age, and likely all species of Dodecatheon, the anthers separate though this plant seems to be slightly mutated.

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References

Gray, Asa. "Essay Toward a Revision of Dodecatheon." Botanical Gazette 11.9 (1886): 231-34. 

Harder, L. D., and R. M. R. Barclay. "The Functional Significance of Poricidal Anthers and Buzz Pollination: Controlled Pollen Removal From Dodecatheon." Functional Ecology 8.4 (1994): 509. 

Hilty, John. "Shooting Star (Dodecatheon Meadia)." Illinois Wildflowers. 

Mast, A. R., D. M. S. Feller, S. Kelso, and E. Conti. "Buzz-pollinated Dodecatheon Originated from within the Heterostylous Primula Subgenus Auriculastrum (Primulaceae): A Seven-region CpDNA Phylogeny and Its Implications for Floral Evolution." American Journal of Botany 91.6 (2004): 926-42. 

Mast, Austin R., and James L. Reveal. "Transfer of Dodecatheon to Primula (Primulaceae)." Britonia Brittonia 59.1 (2007): 79. 

Porter, Sasha. "Mycorrhizal and Microbial Inoculation Affect the Growth and Survival of Native Plants Raised for Restoration." Evergreen State College (2014). 

Reveal, James. "When a Shooting Star Is Really a Primrose." Rock Garden Quarterly 66.2 (2008): 83-93.