Getting a Grip on Goldenrods

One of our most abundant autumn wildflowers, goldenrods are challenging to identify. Some species hybridize and grade into complexes, and individual plants can vary dramatically from the theoretical textbook case. Not only should all of the plant's field marks be taken into consideration, it should also be looked at in the context of its habitat and season.

Unless otherwise noted these photos were taken in early September. Heights are my impressions and estimated heights of the specimens I encountered in the field.

Canada Goldenrod (Solidago canadensis)
Height: Very tall, about 150 cm
Habitat: Relatively wet meadow along the Eastern Ontario Trail

One of our most common goldenrods.

The three prominent veins are characteristic of this species.

The small flowers of goldenrods are less useful for identification purposes, but in some cases the size of the heads or their arrangement can be significant.

Grass-leaved Goldenrod (Euthamia graminifolia)
Height: Tall, about 120 cm
Habitat: Edge of marsh along the Eastern Ontario Trail

The flower clusters and leaves are distinctive; this plant stood out among the neighboring Canada Goldenrod.

Rough-stemmed Goldenrod (Solidago rugosa)
Height: These plants were relatively short, generally less than 100 cm
Habitat: Open wooded areas along the Eastern Ontario Trail

Note the hairy stem and rough texture of the leaves.

The flowers had a distinctly orange cast compared to the more pure yellow of Canada Goldenrod.

The leaves have one prominent central vein; the remaining veins give the leaves a wrinkled quality, especially on their undersides. The upper surfaces have a gritty feel, like fine sandpaper.

Closeups of the hairy stem.

Silverrod or White Goldenrod (Solidago bicolor)
Height: A small plant, perhaps 50 cm tall
Habitat: Very dry, sandy meadow, along a Quinte Conservation Trail about one kilometer southeast of Actinolite.
Photographed: mid August

With its sparse spike of white (occasionally yellow) flowers this small goldenrod isn't apt to be mistaken for another speciers.

A little surprise hidden among the blossoms.

Gray-stemmed Goldenrod (Solidago nemoralis)
Height: Another short goldenrod, most specimens were only 50 cm high
Habitat: Dry upland meadows along the Eastern Ontario Trail

I don't know how this goldenrod got the name "Gray-stemmed", it looks more blue or purple. However, the arching form of the stem with flower clusters borne on the upper side is according to the books.

Again, comparing this plant's blossoms to those of the Canada Goldenrod, the flowers have an almost glowing greenish tint.

Basal leaves are present during flowering.

More Gray-stemmed Goldenrods encountered at another high and dry meadow further west along the trail. To say this species is abundant or ubiquitous would be an understatement.

The undersides of a stem leaf ...

... and a basal leaf.

Bog Goldenrod (Solidago uliginosa)
Height: Small, most were no more 30 cm high
Habitat: Wet, these goldenrods were encountered at the Stoco Fen

The flowering branches tend to grow vertically, following the main stem. These plants didn't bear an abundance of flowers, likely a result of the nutrient poor conditions of their habitat.

Leaves along the upper stem ... note how the leaves clasp the stem, a distinguishing characteristic of this goldenrod.

Views of leaves lower on the stem. (These leaves also clasp the stem but I didn't get any good pictures of this feature.)

Stout Goldenrod (Solidago squarrosa)
Height: Tall, these plants were at least 120 cm in height
Habitat: High and dry hillsides, in woodland clearings along Deer Rock Lake Road north of Flinton

This plant's overall height and flowers borne on short, upright branches stand out in the field. Note that the basal leaves are present during flowering.

The flower heads of this goldenrod are quite large, I've inserted my finger in one of the photos to impart a sense of scale. Also visible are the squarrose or strongly recurved phyllaries – this is a key identifying characteristic of this species.

Photos of the leaves and smooth, hairless stem.

An underside view of an upper stem leaf ...

... a leaf lower on the stem ...

... and a photo of the basal rosette.

Zigzag Goldenrod (Solidago flexicaulis)
Height: These plants were relatively short, from 50 to 100 cm tall
Habitat: Shaded woodland areas along the Eastern Ontario Trail

The broad, deeply toothed leaves and zigzag stem are typical of this species.

The flowers are usually borne on a single upright stem, the ray flowers tend to be sparse.

Views of the leaf.

Wreath Goldenrod (Solidago caesia)
Height: Short, most plants were about 50 cm high or less
Habitat: Shaded woodland areas along the Eastern Ontario Trail

This goldenrod is found in the same habitat and blooms at the same time as the Zigzag Goldenrod. However, the stem of the Wreath Goldenrod has an arching rather than zigzag form, the leaves are lanceolate (lance-shaped) with much shallower teeth, and the flowers grow in clusters from short branchlets at the nodes.

Wreath Goldenrod flower heads are relatively large.

This wildflower is also known as Blue-stemmed Goldenrod. The smooth stems do indeed have a bluish tone – at least on the lower parts of the stem – and are covered in a waxy white bloom that wipes off.

Views of the leaves ... compare to the Zigzag Goldenrod.

Contrary to conventional wisdom goldenrods do not cause allergies. Their pollen is much too large and heavy to be carried on the wind. They rely on insects as pollinators and you'll see a lot of insect species visiting goldenrod flowers.

Goldenrods are popular host plants in another respect. We've already met the fly that causes round goldenrod galls ... Eurosta solidaginis. The goldenrod bunch galls below are formed by a midge, Rhopalomyia solidaginis.

And elliptical galls are courtesy of a moth, Gnorimoschema gallaesolidaginis.

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.

A Study in Irony

By far the most striking caterpillar I have ever chanced upon, this is the larva of Cucullia convexipennis, the Brown Hooded Owlet Moth. The brilliant, contrasting enamel-like colors would look more at home on a piece ceramic. As a rule when an animal boldly advertises its prescence in this fashion it's a warning to a would-be predator that it's toxic. However, I cannot find any resources on the Internet to confirm this supposition.

At close to 50 mm long this is a fifth instar larva and it will be ready to make the change to adulthood soon. It's one of nature's paradoxes that this stunning caterpillar metamorphoses into one of the most nondescript moths imaginable. Here's a link to some images of the adult Brown Hooded Owlet Moth.

The Brown Hooded Owlet Moth's preferred host plant is goldenrod, and they will also eat asters.

The Orange-Humped Mapleworm is another example of a moth which starts out life as colorful caterpillar and transforms into rather mousy moth. This is the adult Symmerista leucitys after making the change.

Pelecinid Wasp (Pelecinus polyturator)

Pelecinus polyturator is the sole representative of its family in our area. This female was over 50 mm in length. Males are seldom encountered, and the wasp's larvae are parasitic on May Beetle grubs.

For more information on these interesting wasps visit BugGuide.Net.