Asteraceae, The Aster Family

At least 64 species of the Aster family grow naturally at Halibut Point, distributed among 27 genera.

Helianthus divaricatus, Woodland sunflower

It's not so hard to recognize the close relationship between asters and sunflowers. Their inflorescences are organized in the same composite fashion of single, brightly colored strap petals emanating from the ray flowers that surround the central button crowded with disc flowers bearing tiny, mute-colored petals.

Hieracium pilosella, Mouse-ear hawkweed

Lactuca  canadensis, Tall lettuce

The relationship between sunflowers and lettuce might not have been so intuitively grasped without a comparison of their respective flowers.

Lactuca biennis, Tall blue lettuce

The plumed seed heads of lettuce and of dandelions suggest that the family includes both of these members. The leaves of both plants are favored in salads.

Taraxacum officianale, Common dandelion

Cirsium vulgare, Bull thistle seeds

Thistle seeds likewise develop "sails" to help with dispersal into new colonies.

Bull thistle flower

The Bull thistle is composed entirely of disc flowers, all button and no surrounding corolla of splendid ray flowers. However it has developed other ways of attracting pollinators.

Arctium minus, Common burdock

The Burdock shows a similar reliance entirely on disc flowers. As in the case of the dandelion, pappus hairs at the base of the flowers develop into a dispersal unit. For the Burdock, hooked spines attach to passing animals to transport the seed head to distant territories.

Bidens frondosa, Devil's beggar-ticks

The hooked spines of Bidens carry seeds off individually rather than as a whole capitulum. However you will have noticed the effectiveness of the dispersal method if you brushed against the plant and picked up scores of seeds on your clothing.

Bidens frondosa flowers

Bidens rely primarily on disc flowers with a few ray flowers forming an incomplete outer circle.

Anaphalis margaritacea, Pearly everlasting

Anaphalis demonstrates another structural variation within the Asteraceae where profuse white sepals surround the yellow disc flowers rather than strap-petal bearing ray flowers.



Erechtites hieraciifolius, American burnweed

This arrangement also characterizes burnweed (above) and tansy (below).

Tanacetum vulgare, Tansy

Cichorium intybus, Chicory

Unusually, Chicory is a member of the Asteraceae bearing only ray flowers. I haven't yet discovered how that qualifies it as a composite. The clues and criteria of taxonomy form a very intricate scope of study that most of us accept as a field for experts, and we botanize innocently with their prescriptions until field guides change and we have to adapt to new names or charts.

Rudbeckia serotina, Black-eyed Susan

Meanwhile, a daisy is a daisy is a....

Asters of Halibut Point

Pictured here at Halibut Point are 16 species of asters, the star-shaped flowers of late summer. They grow in various habitats, from moist to dry and shady to sunny. Distinguishing them accurately in the field is a dedicated business that may require a comparison of details in the leaves, stems, and expression of the plant as well as flowers.

By the time asters come into bloom it's been months since the dazzle of spring. Our senses have been dulled  by a long green interlude of pleasant traipsings on trails and shoreline. The landscape is tiring of heat and bright light. Dry areas are fading. The onset of aster season refreshes our delight in the woods and moors with the suddenness of new flowers and a curiosity for botanical intricacies. Whether it's coming to an oceanside panorama of violet blossoms or bending on hands and knees to study a puzzle in a thorny thicket, we perk up for a succession of aster events from August to November.

Molecular analysis by our generation of botanists adds to their findings of likenesses and distinctions in the evolutionary structure of plants. Where our local aster species used to be considered members of one worldwide genus Aster in the family Asteraceae, they have been assigned in current taxonomy to various genera within that family. None of them any longer carries the genus name Aster. The photographs below are organized within this re-classification.

The genus Symphyotrichum

S. cordifolium - Blue wood-aster

S. dumosum - Bushy American-aster

S. ericoides - Heath aster

S. laeve - Smooth American-aster

S. lanceolatum - Lance-leaved American-aster

S. lateriflorum - Calico American-aster

S. novae-angliae - New England aster

S. novi-belgii - New York aster

S. racemosum - Small white aster

S. undulatum - Wavy-leaved aster

The Genus Eurybia

E. divaricata - White wood-aster

E. macrophylla - Large-leaved wood-aster

E. schreberi - Schreber's wood-aster

The Genus Ionactis

I. linariifolia - flax-leaved stiff-aster

The Genus Oclemena

O. acuminata - Sharp-toothed nodding-aster, whorled aster

The Genus Sericocarpus

S. asteroides - Toothed white-topped aster

Goldenrod and Asters

Aster and goldenrod on the quarry wall

Goldenrod and asters are companionable plants at Halibut Point, finding their way into similar niches of many types. They are easy for Park visitors to recognize in a general way, particularly when in flower. They are the yellow ones and the blue ones of late summer.

Seaside goldenrod (Solidago sempervirens) and White heath aster (Symphyotrichum ericoides)

With a little closer look more distinctions of color and form appear, especially in the case of the asters. The blues vary from purple to white, the postures from tall to prostrate. The star shapes for which they are named show subtly different configurations. The leaves of various species range from broad to needle-like. Diversity abounds.

Flax-leaved aster (Ionactis linariifolia) and Downy goldenrod (Solidago puberula

The asters are multi-colored daisies. Their central button is actually a dense cluster of tiny disc flowers capable of producing seeds. Each disc flowers is ringed by five fused petals. A row of ray flowers encircles the button. Each ray flower extends a large strap-like petal outward. Collectively they make up the showy corolla. This composite ensemble comprises a bright and business-like inflorescence that attracts pollinators, children, and florists. The composite family may be the most widespread flowering plant group in the world.

With such great distribution the composites not surprisingly present a taxonomic wonderland to botanists, who currently recognize over 32,000 different species in 1,900 genera. All of these are distinguished by the daisy grouping of disc flowers, though not all combine them with large-petaled ray flowers. In botanical language they are called the Asteraceae. Previously, and still acceptably, they were termed Compositae.

In evolutionary time the daisy principle has ramified into a great many common plants. I've come across a considerable number of species within 33 genera of Asteraceae at Halibut Point, including sunflowers, thistles, wild lettuce, and dandelions.

Aster and Grass-leaf goldenrod (Euthamia graminifolia)

You may be surprised on careful examination to notice that goldenrod flowers are built on the daisy structure. That fact places them within the Asteraceae. They are close cousins of the aster. We saw in the last posting that our local goldenrods are split among two different genera, Solidago and Euthamia.

The captions on the pictures above hint at recent complexities in classifying our familiar asters. The over-arching genus Aster no longer applies to American species. The designation 'true asters' is reserved for certain relatives with evolutionary precedence from the Old World. Anyone who wants to stay up to date with botanical conversations will have to learn how to remember and pronounce some daunting terms for our latecomers.

In the next posting we will go afield at Halibut Point to consider eleven species growing there.

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.