Family: Daisy Family (Compositae)
Origin and Distribution: The genus Solidago includes approximately 100 species of goldenrods that are mostly native to North America. Although 22 of these species are naturalized around Ohio, only Canada goldenrod has a distribution encompassing the whole state. Canada goldenrod is also well established in the northeastern and north central U.S. and southern Canada. The species does not tolerate frequent disturbances, so it is mainly found growing in perennial crops, abandoned fields, ditches, roadsides, riverbanks, creek margins, open woodlands, and floodplains. It prefers moist conditions and medium textured soils. Canada goldenrod usually does not establish on very wet or dry sites, and it is fairly intolerant of shade.
Plant Description: Canada goldenrod is a perennial distinguished by numerous small yellow flowers located in pyramid-shaped clusters at the top of individual, unbranched, leafy stems. Flowers are crowded onto numerous backward-curved stalks that originate at a central axis and are arranged more or less horizontally. Leaves are lance-shaped, tapered at both ends, hairless on the upper surface, hairy underneath, and sharply toothed on the edge. Leaves are described as being 3-nerved, meaning the midrib and 2 parallel lateral veins are prominent. Plants reproduce by way of short rhizomes (horizontal underground stems) emerging from the base of aerial stems and by wind dispersed seeds.
- Root system - The extensive root system is very deep and fibrous with 2- to 5-inch-long rhizomes (horizontal underground stems) emerging at the base of aerial stems. Rhizomes are often reddish.
- Seedlings & Shoots - Seed leaves (cotyledons) are small and elliptical. Young leaves are round, bluish green, pale beneath, and bitter tasting. The first leaves produced are basal and hairless or with a few hairs on the edge. Later leaves are rough due to hairs on the edge and underneath on the veins. Young leaves are 3-nerved, meaning the midrib and 2 parallel lateral veins are prominent. Young stems are purple-stained.
- Stems - Stems are 1 to 5 feet tall, leafy, mostly unbranched, slender, hairless in the lower half, and have small soft hairs in upper half below the flowers.
- Leaves - Leaves are alternate (1 leaf per node), narrow, lance-shaped, tapered at both ends, sharply toothed around the edge, hairless on the upper surface, and hairy beneath especially on the veins. Leaves are described as being 3-nerved, meaning the midrib and 2 parallel lateral veins are prominent. Basal leaves form but fall off early leaving only stem leaves that are all nearly the same size. Leaves lack stalks (petioles), so bases attach directly to the stem.
- Flowers - Flower heads form in dense, elongated, pyramid-shaped clusters. Each flower head consists of 9 to 17 yellow ray flowers surrounding fewer than 10 yellow disk flowers. Flower heads are less that 1/8-inch wide.
- Fruits & Seeds - Single-seeded fruits are orange, approximately 1/20 inch long, and tipped with a tuft of white hairs (pappus).
Similar Species: Other goldenrod species (Solidago spp) are very similar, and taxonomists have not yet agreed on a single taxonomic treatment. However, several characteristics can be used to identify Canada goldenrod such as its lack of large basal leaves, which form early but then fall off leaving only stem leaves that are all about the same size. Other distinguishing features include the manner that flower stalks attach to a central axis, hairs on the upper half of the stem below the flowers, and 3-nerved leaves.
Biology: Flowering begins in mid-August and continues through October. Plants usually do not flower until the second year of growth. Goldenrod plants growing in an old field in Ohio averaged 3,070 seeds per plant. A pappus at the tip of each seed aids in wind dispersal; goldenrod seeds released 3 feet off the ground traveled an average of 2 feet in a 5-mph wind. Rhizomes are usually not produced until after the first year of growth. Several rhizomes grow outward from the same root crown resulting in a circular cluster of stems between 2 to 5 inches apart. Patches of shoots produced by rhizomes arising from a single root system were observed growing up to 8 feet wide. To control, the site should be shallowly plowed in autumn and a crop planted the following year that tolerates cultivation. In Europe, biological control measures are used to control this introduced pest from North America.
Toxicity: None known. Goldenrods are often blamed for causing hayfever because they flower during allergy season. However, the true culprits are ragweeds (Ambrosia spp.). Goldenrod flowers are mainly insect pollinated, so the flowers are showy to attract insects and pollen is relatively heavy and sticky compared to that of ragweed. It is unlikely that the wind-blown allergens affecting hayfever sufferers include appreciable amounts of goldenrod pollen.
Facts and Folklore:
- 'Solidago' was taken from the Latin 'solidus' meaning 'whole' and likely referring to the supposed healing properties of this genus.
- Young Canada goldenrod shoots remain connected by way of rhizomes for up to 4 years.