By Tom Schweich
A common blue wildflower along Golden’s trails is “Blue Flax.” You will see it in all our open spaces and most of our parks. This may be our native Linum lewisii Pursh or the non-native Linum perenne L. or … a hybrid of the two.
Our native blue flax — Linum lewisii Pursh — was described by Pursh (1814) from a collection by Lewis & Clark (Those guys again!), found in the valleys of the Rocky Mountains and on the banks of the Missouri River. Typically, descriptions of new plants are written from a dried specimen, but Pursh wrote that he described the plant from a live specimen. How did that happen? Sometimes seeds can be found in dried plant collections. Perhaps there were some native blue flax grown from seeds in A. B. Lambert's London garden, where Pursh was working while he wrote his Flora of North America.
The non-native blue flax — Linum perenne L. — is native to central Europe east to Siberia and was well-known to botanists in the 18th century.
Genetic data shows that the blue flaxes are very closely related (McDill, et al., 2009). So close that some botanic authors treat our native L. lewisii as a variety of the Eurasian L. perenne, which is thought to be an ancestor of our native blue flax. It probably migrated to North America across the Bering land bridge 3 to 4 million years ago.
As it happens, the non-native blue flax is often planted (highway departments are the usual culprit) because the seed is more readily available. Or sometimes seed that was sold as the native blue flax is later determined to be non-native blue flax. This happened with a horticultural selection called “Appar.”
How do you tell the two flaxes apart? It’s not easy. Our native blue flax lost a very subtle technical trait called heterostyly, about the relative lengths of stamens and styles. So, the absence of one very technical trait determines native blue flax, whereas the presence of that trait shows non-native blue flax. There are also intermediate or ambiguous plants because the two flaxes hybridize. Sitting in the field beside a blue flax plant and carefully examining all the flowers, sometimes I can tell which blue flax it is, and sometimes I cannot.
Regardless of which blue flax it is, blue flax is a very attractive plant along our trails. It is also easy to grow from seeds in the garden. I don’t do anything special to prepare the soil or seeds. Mostly I just throw the seeds out when it starts to snow. Blue flax is a short-lived perennial and will come back year after year while spreading slowly by seed.
References
McDill, Joshua, Miriam Repplinger, Beryl B. Simpson, and Joachim W. Kadereit. 2009. The Phylogeny of Linum and Linaceae Subfamily Linoideae, with Implications for Their Systematics, Biogeography, and Evolution of Heterostyly. Systematic Botany. 34(2), pp. 386-405. https://www.researchgate.net/publication/235443463
Pursh, Frederick. 1814. Flora Americae Septentrionalis; or, A Systematic Arrangement and Description of the Plants of North America. 1. London: White, Cochrane, and Co., 1814. https://www.biodiversitylibrary.org/item/1987#page/251/
