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.
