Know Your Natives – Wreath Goldenrod

Wreath goldenrod (Solidago caesia) of the Aster or Sunflower (Asteraceae) family is one of the smaller goldenrods that occur in Arkansas. In the U.S., it is found from Texas to Wisconsin and thence east to the Atlantic and Gulf Coasts. In Arkansas, it occurs across the state except for portions of the Mississippi Alluvial Plain and West Gulf Coastal Plain. The genus name is from Latin for “to make whole” or “to heal” in reference to purported health benefits derived from some species of the genus. The specific epithet, also from Latin, for “slate blue” in reference to stem color. Other common names include blue-stem goldenrod and woodland goldenrod.

Wreath goldenrod, a plant of mesic soils in upland deciduous woods, well-drained lowlands and bluff areas, is a herbaceous perennial that propagates by seed and rhizomes. Plants that have a half-dozen or more compact-growing stems are probably growing from a caudex supported by many long, slender, white, radiating, rope-like roots. While single-stem plants are probably growing from a rhizome’s tip or from node junctions along its length. The white, near-surface, stubby rhizomes are slow growing so that non-aggressive colonies may develop.

Stems, a light green when young, typically become bluish to purplish (on the sunny side) with an overcast of whitish bloom (i.e., a thin, waxy coat). The smooth, slender, terete stems, reaching 3 feet long, are ascending and arching, but frequently stems become reclined. Stems typically have a half-dozen or so axillary lateral branches mid-stem, well below the tip. Lateral stems, with widely varying length to about 1 foot long, have the same appearance as primary stems. The lower portions of primary stems tend to be straight, while distally the more slender portions are slightly zigzagged. Lateral stems tend to be slightly zigzagged their entire length. Individual stems that have lateral stems appear rather “skeletal” due to the spacing of the rather sparsely leafed lateral stems. All stems are mostly glabrous (hairless).

Wreath goldenrod - Solidago caesiaPhoto 1: Current-year stems grow from tips of rhizomes as new rhizomes emerge along their length. Stub of a previous-year stem can be seen at lower center. Photo October 24.

Wreath goldenrod - Solidago caesiaPhoto 2: Leaves of springtime stems have wide serrations. Minor marginal pubescence can be seen on lower portion of several leaves. Photo March 5.

The alternate leaves of wreath goldenrod, randomly arranged around the stems, are dark green adaxially (above) and a lighter green abaxially (below). Stem (cauline) leaves vary from broadly lanceolate below, to lanceolate at mid-stem, to narrowly lanceolate distally. They measure up to 5 inches long and ¾ inch wide, become gradually smaller toward the apex and even minute along lateral branches within the inflorescence (see below). Cauline leaves gradually taper to an acuminate tip and a sessile or nearly sessile base. Most leaf margins are serrated, with teeth of basal leaves wider and less pointed and those of cauline leaves increasingly acute and sharply pointed. Uppermost small cauline leaves (½ inch long and ⅛ inch wide and smaller) may be entire. Leaves are smooth and nearly glabrous, with minor marginal pubescence at the base. All leaves in the upper portion of the plant subtend a lateral stem or inflorescence (see below). Basal leaves drop off as the plant approaches flowering, and lower cauline leaves, if dry conditions occur, drop off as well during flowering.

Wreath goldenrod - Solidago caesiaPhoto 3: This plant has a dozen stems growing from a central caudex. Photo March 26.

Venation is pinnate. Veins of the adaxial surface are the same color as the leaf blade while, on the abaxial surface, the midrib and secondary veins are a light green. The midrib of the adaxial surface is suppressed while secondary veins may be slightly suppressed. Tertiary veins of upper surface are obscure while tertiary veins of lower surface are a dark green color such that a reticulated pattern is easily seen.

The inflorescence of wreath goldenrod, appearing for about a month in mid-fall, consists of small terminal and axillary clusters of composite flower heads. Flower heads reach anthesis from distal ends of stems, progressing downward. Clusters consist of 2 to 9 loosely arranged flower heads in short racemes. The number of flower heads in clusters generally decreases from stem apex, downward. All flower heads in a cluster reach anthesis at the same time and a fair number of clusters along a stem blooms at the same time, thus producing an arching wreath-like appearance. In cases where racemes appear to be especially long, one is actually seeing a very short lateral stem with tiny leaves, with each leaf subtending a flower head or two. Flower heads, drawn to sunlight, become secund (arranged along one side).

Wreath goldenrod - Solidago caesiaPhoto 4: Arching stems often recline. Flower clusters become oriented toward sunlight. Sunny sides of stems become bluish to purplish with age. Photo October 15.

Clusters are composed of up to ten or so tiny, bright yellow, loosely arranged composite flower heads. About ¼ inch long (including peduncle), heads comprise three to four pistillate (no stamens) ray florets surrounding up to eight or so perfect (stamens and pistils) disk florets. Ray florets have broadly oblong ligules (the flat, strap-shaped, laterally extended part of a ray flower), with several pleats and an apical notch, as well as slender styles with pointy-tipped, bifurcated stigmas. Disk florets are tubular with acutely triangular flaring lobes, and five stamens with short filaments and anthers, fused into a ring, that clasp the developing slender style. As the style emerges from the ring of anthers, it pushes out and exposes their pollen, to be carried away by pollinating insects. Anthers then wither, becoming white. Once fully exserted, the pair of linear stigmatic surfaces divides and becomes receptive to pollen, typically from other flowers–and most productively, from flower heads on other plants. (There is, nevertheless, much self-pollination in the sunflower family.)

Wreath goldenrod - Solidago caesiaPhoto 5: “Cluster” at left is composed of flower heads subtended by tiny leaves. Orange arrow indicates flared corolla lobes of a disk floret. Red arrow indicates style of a ray floret. Lavender arrow indicates anthers of a disk floret. White arrow indicates emerging style of a disk floret surrounded by ring of shrunken, whitened anthers. Photo October 17.

Wreath goldenrod flower heads are set in cup-like involucres composed of spirally arranged, tightly imbricated, oblong bracts (phyllaries). Heads have very short peduncles attached to short rachises so that racemes have a cluster-like appearance. Phyllaries transition below to tiny pedunculate bracts.

Wreath goldenrod - Solidago caesiaPhoto 6: Involucres are composed of elongate, imbricated phyllaries that transition into bracts along peduncles. Note dark green tertiary venation of lower side of leaves and marginal pubescence at leaf bases. Photo October 17.

Fertilized florets produce flattened, 1/16-inch-long, minutely pubescent, elongate achenes (often termed cypselae in this family–single seeded, indehiscent, nutlet-like fruits), each topped with a pappus of silvery hairs. Dispersal is by wind.

This fall-blooming goldenrod species would work well in an open woodland setting that has mesic soil. Among the goldenrods, it is a more dainty species with smooth leaves and stems. Bright yellow clusters of flower heads are showy and the plant’s open structure is attractive. It is not aggressive. As with all goldenrods, wreath goldenrod attracts a variety of small insects and butterflies. Fall allergies, blamed on goldenrods, are primarily caused by ragweeds (Ambrosia spp.), wind-pollinated members of the same Sunflower family.

Wreath goldenrod is one of 28 species of goldenrods (some with additional subspecies or varieties) known to occur in Arkansas, of which two other species have somewhat similar flowering characteristics: zigzag goldenrod (Solidago flexicaulis) and Ouachita goldenrod (Solidago ouachitensis), both of rather limited occurrence in the state. Zigzag goldenrod can be distinguished by its significantly wider to oval petiolate, heavily serrated leaves and its non-glaucous green zigzag stems. Ouachita goldenrod, quite similar to wreath goldenrod and occurring only on north-facing slopes of the Ouachita Mountains, can be distinguished by its larger leaves on unbranched, more upright stems, non-secund flower clusters, and composite flower heads each with only one ray floret.

Article and photographs by ANPS member Sid Vogelpohl

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