Goldenrod and Science, Part 2 - Systematics

I do not know what I may appear to the world; but to myself, I seem to have been only like a boy playing on the seashore, and diverting myself now and then in finding a smoother pebble or prettier shell than ordinary, while the great ocean of truth lay all undiscovered before me.... Isaac Newton

Seaside goldenrod, Solidago sempervirens

If Isaac Newton (1643-1727) were walking on the seashore at Halibut Point, the pretty yellow flowers (above) would have stirred his mind. To reach them he would have passed similar-looking plants in various upland environments. He would have thought about their similarities and diversities.

Elliott's goldenrod, Solidago latissimifolia

By the end of Newton's life a Swedish scientist named Carl Linnaeus (1707-1778) had begun formulating the classification system that we still use to sort out our encounters with organic life. We can now refer to any living thing by a unique two-word term that names its genus (first) and species. That singular name also gives a key to the plant's relationship to all other organic groups, through an evolutionary ladder tracing kinship to the entire plant kingdom and beyond. This is the simple, universal system known as binomial nomenclature.

As a general defining principle, members of a species can reproduce with each other but not with other, though similar, organisms. Finer distinctions in the characteristics of a particular plant that do not prevent its cross-breeding with other members of its species, are called subspecies, varieties or cultivars. The subspecies designation results in a trinomial such as the Solidago latissimifolia subsp edisoniana mentioned in the previous posting. Such cases may come about when two or more population groups of a species with distinctly different appearances, that do not interbreed due to geographic isolation, have fertile offspring when brought back in contact.

Notable traits within a species may be pursued or enhanced by hybridizers. They often result in an informal descriptor being appended to the binomial, such as Solidago rugosa 'Fireworks', which is a horticultural selection. Its progeny by seed might quickly revert to a type less desirable to gardeners if allowed to pollinate with other members of its species. Purity of the strain calls for restrictive sexual management, or else single-parent propagation (cloning).

These intricacies reflect the challenges to the field of taxonomy that attempts to fit all observable life into a universal system of classification.

Solidago latissimifolia flowering branches

In nature purity is not only unknown but counter-progressive. Natural life is constantly altering due to inner (genetic) or outer (environmental) influences. Noticeable variations in appearance do not reach the point of speciation unless accompanied by, or dictated by, sufficient genetic change to prevent the plant from inter-breeding with others. Sexual incompatibility with its original group may happen gradually, such as in geographic isolation during glaciations, or more suddenly in genetic mutation.

Solidago latissimifolia flower detail

The individual flower is the showy agent of a flowering plant's self-perpetuation. It has traditionally been examined by botanists for details in parsing the essential and exclusive characteristics of a species. Sometimes very minute distinctions in flower structure must be presented in your Field Guide to identify a species. Hopefully there is also more obvious morphological evidence such as leaf characteristics at hand for identification, or habitat indications.

A goldenrod-like discovery at Halibut Point

In exploring Halibut Point Isaac Newton would have been intrigued by a plant with narrow grass-like foliage and flowers for all the world like a goldenrod.

Solidago graminifolia (?)

Until recently Field Guides have presented this plant as Solidago graminifolia, the grass-leafed goldenrod. But lo and behold, current editions have re-classified it into a new genus as Euthamia graminifolia. The re-designation was made primarily because of distinctions in the arrangements of flower heads, gland-dotted leaves, and DNA sequence data.

Euthamia graminifolia

The robust, ongoing diversification of life forms challenges the search for an all-inclusive model of classification. Theories of a perfect taxonomic system undergo continual debate with new discoveries, perspectives, and tools. It is an area of very broad and also minute debates. Recently it has generated the concept of clades, which sees a species as the smallest lineage distinguishable by a unique set of either genetic or morphological traits, but where no claim is made about reproductive isolation. Thus the fact that traditional species can be seen to interbreed sometimes, across close genetic boundaries, does not invalidate the utility of the attempted scientific organization.

In the next posting we will look to the ladder of classification to see justification for the taxonomic association of yellow goldenrods with blue asters.