A Short Primer on "Aster"ology

Summer is waning fast and early autumn is upon us, and with the season comes a last rush of bloom before the hard frosts arrive. The Aster family, formerly known as Composites, is well represented among the wildflower species. Since my knowledge of asters and goldenrods leaves something to be desired (in truth, it's virtually non-existent) it seems like a good time to take the horns by the bull and redress this situation. Two good resources toward this end are Walter Muma's Ontario Wildflowers and The ROM Field Guide to Wildflowers of Ontario.

In order to understand the species accounts it's necessary to learn to identify the various parts of the flowers. This sketch of a cross section through a typical aster below is based mostly on the diagram on Page #143 in the ROM guide (but it is my interpretation, so any errors and/or omissions are mine). Briefly, the defining characteristic of family Asteraceae is several small flowers or florets sharing a common receptacle. The florets are surrounded by rows of bracts called phyllaries, with a set of phyllaries combining to form a vase-like structure called an involucre.

The word composite usually brings to mind an image of a flower much like in my drawing: a central group of disk florets, surrounded by an outer ring of ray florets. The disk florets are composed of five petals fused into a tube-shaped corolla above the ovaries, and within the corolla are five stamens (the male flower parts) forming another ring surrounding the female style. Although very different in appearance the basic structure of the more showy ray florets is the same, except the tube of the corolla is lengthened on one side to form a strap-like ligule. You can often see the tips of the fused petals, which look like little teeth, on the ends of the ligules on flowers such as dandelions or hawkweeds.

Now let's compare the labels in the diagram above to the reality of what we see in the field. The phyllaries can be seen in these images of a Heath Aster (Symphyotrichum ericoides) ...

... a Purple-stemmed Aster (Symphyotrichum puniceum) ...

... and a Spotted Knapweed (Centaurea maculosa). In fact, the dark tips on the phyllaries are how this plant its name.

Phyllaries can be mistaken by novices such as myself for sepals, but in the aster family sepals are either absent or modified into a pappus made of bristles or hairs. And the pappus itself is attached to a small dry fruit called an achene – often mistaken for the flower's seed.

The pappus generally aids in seed dispersal and can be as little as the hooks on the achene of a beggar tick or a few tufts on the achene of a goldenrod.

Or it can form a full blown parachute such as seen on these seed heads of Yellow Goatsbeard (Tragopogon dubius) ...

... or Coltsfoot (Tussilago farfara).

A flower head made up of both disk and ray florets is called a radiate head, as in the familiar Ox-eye Daisy (Leucanthemum vulgare) ...

... and the Black-eyed Susan (Rudbeckia hirta).

In the world of nature there seem to be as many exceptions as there are rules. Flower heads can be made solely of disk florets, in which case the are called discoid heads. Some notable examples are the Pineapple Weed (Matricaria discoidea) ...

... the Tansy (Tanacetum vulgare) ...

... and the Common Burdock (Arctium minus). Most people who have spent time outdoors are acquainted with the very efficient hooks on the phyllaries, used to facilitate dispersal of the plant's fruit and hence seeds.

The flower heads of Pearly Everlasting (Anaphalis margaritacea) are also composed of disk florets, surrounded not by ray florets as one might expect, but by several rows of pearly white phyllaries.

Lastly, flowers heads can be composed solely of ray florets, in which case they are called ligulate heads, as in the ubiquitous Dandelion (Taraxacum officinale) ...

... and the Devil's Paintbrush (Hieracium aurantiacum).

That pretty much covers the basics. But many people would ask "Why bother with all this technical stuff?". The wildflower in the following three images was encountered in the forest at the Vanderwater Conservation Area. These images sat in my unidentified file for a close to a month, and the only reason I was able to eventually put a name with the images was that I stumbled across a an inset photo at the bottom of Page #165 in the ROM field guide.

With the 20/20 vision of hindsight it's obvious I should have taken more photos of different parts of the plant. In particular had I photographed (or at least had a look at!) the underside of the flower head I would have noted the presence of phyllaries. It would have been clear that the groups of tiny white flowers were disk florets (not panicles or umbels) and that this plant was a composite, leaving fewer potential candidates to sift through. A little knowledge would have made life a lot simpler ...

In fact, this wildflower is White Snakeroot (Eupatorium rugosum), a close relative of the well known Boneset (Eupatorium perfoliatum).

About a month later I found this solitary late bloomer found growing along the trail and had a chance to study this plant more thoroughly.

A side view of the flowers – clearly disk florets enclosed by phyllaries.

Vernal Vegetation ... The First Flowers of Spring

Many low growing woodland herbs have to get off to an early start and live hard and fast. They must bloom, produce seeds, and photosythesize food to store in their bulbs and tubers for next year before the taller shrubs and trees leaf out and bar the sunlight. The Bloodroot (Sanguinaria canadensis) has already blossomed; all that remains of these members of the Poppy family are the distinctive leaves.

Dense yellow carpets of Marsh Marigold (Caltha palustris) brighten up the subdued woodland corners. These plants prefer areas where the soil is saturated with water. The Marsh Marigold is a member of the Buttercup family and like many of its relatives it contains toxic irritants.

The wildflowers captured in these images are only a very few that were encountered along the Eastern Ontario Trail within three kilometers east of Tweed. The lily family is well represented. The Large-flowered Bellwort (Uvulaire grandiflore) with its gracefully drooping blossoms is found in the same woodland habitat as Trilliums.

No collection of spring floral images would be complete without our provincial flower, the ubiquitous White Trillium (Trillium grandiflorum). The Red Trillium (Trillium erectum) or Wake Robin seems to be a less common species locally; I only encountered one specimen last spring.

Even when not in bloom the Trout Lily (Erythronium americanum) is easily identified by its mottled leaves. These lilies spread by corms and are often found growing in large colonies in moist areas.

The Cut-leaved Toothwort (Dentaria laciniata), or Crow's Toes. I've walked past this member of the Mustard Family many a time in the past but never stopped and took the time to find out what it was. There's a difference between looking and seeing, and always something new to learn ...

The fragile star-like flowers of the Narrow-leaved Spring Beauty (Claytonia virginica) add a touch of color to last autumn's leaves covering the woodland floor. This flower is a member of the Purslane family, a relative of the gaudy Portulacas cultivated in gardens.

Open areas along the sides of the trail are suitable habitat for violets. The following two species are probably the Common Blue Violet (Viola sororia), or possibly a Marsh Blue Violet (Viola cucullata), and the less common but by no means rare Downy Yellow Violet (Viola pubescens). I’m not a hundred percent certain as to species ... until I started researching these images, I had no idea there were so many kinds of violets ...

Coltsfoot also prefers less shaded areas. The flower and seed head superficially resemble a dandelion: both are members of the Aster family. However, the stems of Coltsfoot bear reddish brown scales and the basal leaves are very different from those of the dandelion.

Virginia Strawberries (Fragaria virginiana) may be found where woodlands give way to fields.

I'm not sure exactly which species of Low Blueberries (Vaccinium sp.) this is, but these small shrubs with their characteristic bell-shaped flowers thrive in rocky areas with poor soil cover.

Some plants like to live dangerously, Saxifrage can be found growing on rocky outcrops. This is probably Saxifraga virginiensis.

The Canada Columbine (Aquilegia canadensis), a fitting name for a plant living in a habitat found on the edge of the Canadian Shield, is another flower that’s often found hanging onto ledges with little soil. In terms of form and color this member of the Buttercup family is my favourite wildfower.