Some Notes on Recognition of the Members of the Solidago canadensis
Polyploid Complex in Central Pennsylvania

Solidago gigantea (tetraploid & diploid)
Solidago canadensis (diploid)
Solidago altissima (hexaploid)
Wet spots in open fields, meadows, ditches. Occasionally under shade of deciduous woods. Generally found in open areas,
but avoids the very dry portions
of fields, where S. altissima tends to predominate.
Most cosmopolitan of the three ploids in habitat preference, can grow side-by-side with other two but usually found by itself in very dry habitats (hillsides, roadbanks, backlogs, etc). 
Totally glabrous (smooth) from ground level up to inflorescence. Often with a waxy whitish bloom that gives the stem a pale blue or purple cast.  Distinctive. Has villous (woolly, long-haired)
pubescence from inflorescence 1/2 to most of the way to the ground, often tapering off sharply on the bottom few inches.
Entire stem is pubescent (hairy), usually with very short, almost granular-gritty hairs.  Some forms, however, show a long, woolly pubescence similar to S. canadensis. Separate using leaf characteristics.
Very sharply serrate (with small toothed edge), always totally glabrous above.  Usually smooth below, although some plants show pubescence on major leaf veins. Sharply serrate to dentate (deeply cut, 
sawtooth teeth), smooth or slightly scabrous (course) above, with pubescence on underside but confined almost entirely to the three major leaf veins.  Leaves can be very broad on some plants.
Shallowly serrate to subentire (almost no teeth); almost always smoother edged than leaves of S. canadensis, but highly variable. Usually very scabrous above and with pubescence over entire underside, not just on veins.  Leaves tend to be more lanceolate (narrow) than S. canadensis.
Not needed to identify this distinctive species.  Bloom starts in very early July-early August. Involucral bracts usually 2-3 mm high, ray flowers about 2.5 mm long.  Bloom starts in late July.

(click for diagram)

Involucres tend to be large (> 3 mm), as do ray flowers.  Inflorescences can sometimes be
enormous.  Bloom commences later, usually August.
Easiest ploid to identify.  To the south, it seems to be totally free of ball galls, but is a common host to the elliptical gall and occasional rosettes galls. In northern areas, such as New England and the upper midwest ball galls are common. Not rare, but never as plentiful as S. altissima. Like S. gigantea, seems to be free from all but the occasional ball gall.  Often tricky to separate from S. altissima. This species often looks darker green than S. altissima.  Not common, doesn't seem to occur in huge unbroken clones like S. altissima. More common in northern New England. Any plant in central PA with a ball gall is liable to be this species.  Also host to elliptical, rosette, and various leaf galls.  Can grow in amazingly barren ground, i.e., railroad embankments.  Abundant.

Figure One: Comparison of S. altissima vs. S. gigantea mature plants

Notes for Figure One: a) inset of  S. altissima's scabrous (hairy) stem, b) S. altissima's pubescent (fuzzy) leaf underside, c) S. altissima's relatively thick rhizome, d) S. gigantea's glaucous (smooth and waxy) stem, e) S. gigantea's glaucous leaf underside, and f) S. gigantea's relatively thin rhizomes.

Figure Two: Comparison of S. altissima vs. S. gigantea galls

Notes for Figure Two: a) S. altissima's gall is scabrous (hairy), while b) S. gigantea's gall is glaucous (smooth and waxy).

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Key to Gall Contents
Gall Flies (Eurosta)
Insect Parasites and Predators
Avian Predators
Solidago and Eurosta Links
Ecology and Evolution
Solidago Biology