25. Solidago L. (goldenrod)
Plants perennial
herbs, often with short- to long-creeping rhizomes, less commonly with a short,
branched, somewhat woody rootstock. Stems 1 to several, erect, ascending, or
less commonly spreading to pendant, usually with few to many ascending to
spreading branches above the midpoint, with fine to coarse, longitudinal
ridges, glabrous or variously hairy. Basal and lower stem leaves either absent
at flowering or present (and then the largest leaves on the plant), sessile or
short- to long-petiolate. Stem leaves gradually or relatively abruptly reduced
toward the tip of the stem either from about the midpoint or from the base,
sessile or short-petiolate, the blade variously shaped, usually sharply pointed
at the tip, tapered to a slender or slightly expanded but not clasping base or
less commonly truncate to rounded and slightly clasping the stem, the margins
entire to coarsely toothed, sometimes also roughened with minute, stout,
ascending, stiff hairs, the surfaces glabrous or variously hairy.
Inflorescences variously consisting of axillary clusters, or terminal, then
either narrow and racemelike with clusters along the main axis or open to
dense, pyramidal or flat-topped panicles, the heads solitary or more commonly
in small clusters, sometimes all or mostly oriented upward (in species with
pyramidal panicles), the stalks subtending the heads mostly short, usually with
relatively few minute, scalelike, linear to narrowly oblong bracts to 0.4 mm long,
the inflorescence branches often also with reduced, leaflike bracts
conspicuously shorter than the main foliage leaves. Heads radiate. Involucre 2–8
mm long, cup-shaped to nearly cylindrical. Involucral bracts in 3–6 usually
unequal, overlapping series, variously shaped, the ascending tips (the lower
series sometimes spreading in S. petiolaris) rounded to bluntly or
sharply pointed, the midvein 1 or less commonly 3–7 and often slightly
thickened and translucent, entirely straw-colored to light yellow or with an
often short, elliptic to obovate green area toward the tip, glabrous or hairy,
not resinous. Receptacle flat or slightly convex, with low, toothlike ridges
around the attachment points of the florets, uncommonly with a few chaffy
bracts toward the margins. Ray florets (1)2–15, pistillate, the corolla well
developed but relatively short, mostly spreading, yellow (white in S.
ptarmicoides; see also the discussion of S. bicolor at the beginning
of the Astereae treatment), not persistent at fruiting. Disc florets 2–35,
perfect, the corolla relatively short, yellow (white in S. ptarmicoides),
not persistent at fruiting. Pappus of the ray and disc florets similar, of
numerous (25–45) slender, finely barbed bristles about as long as the corollas,
the innermost sometimes slightly thickened toward the tip, white or off-white.
Fruits (0.5–)1.0–4.0 mm long, obovoid to more commonly narrowly obovoid to
nearly cylindrical, usually slightly flattened, often slightly several-angled
in cross-section, 5–8(–10)-nerved, the surface glabrous or hairy, straw-colored
to brown. About 100 species, North America, South America, Europe, Asia.
The generic
concept of Solidago accepted here is broader than that embraced by some
other botanists (Nesom, 1993a, 2000). In particular, some authors prefer to
segregate Oligoneuron Small for six eastern North American species with
generally flat-topped inflorescences, relatively broad involucral bracts with
more or less parallel veins, and minute differences in achene anatomy. In
Missouri, this generic controversy involves three morphologically unusual
species, S. ptarmicoides, S. riddellii, and S. rigida. Anderson
and Creech (1975) felt that the two groups should be united based on their
investigation of leaf anatomy. Nesom’s (1993a) morphological analysis of the
complex yielded ambiguous results, as did a recent molecular analysis of ITS
sequences in the tribe (Beck et al., 2004). However, molecular studies of
chloroplast DNA variation by Zhang (1996) supported the hypothesis that the Oligoneuron
species are members of the Solidago lineage, a conclusion accepted in
the floristic treatment of Ontario goldenrods by Semple et al. (1999), as well
as most other recent floristic manuals for areas surrounding Missouri (Barkley,
1986; Gleason and Cronquist, 1991). The present treatment has benefited from
early discussions with John Semple of the University of Waterloo concerning
generic, specific, and infraspecific limits.
Two aids to
identification in this morphologically variable genus are the inflorescence
type and the arrangement of the leaves. Missouri species are separable into
three main inflorescence types. A small group that some botanists segregate as
the genus Oligoneuron (see the preceding paragraph) comprises species
with relatively flat-topped or rounded, paniculate inflorescences having the
heads in small clusters at the branch tips. Another group has either axillary
clusters of heads or narrow, elongate terminal inflorescences that often appear
spicate or racemose with the heads in small clusters along the main axis, but
can have the heads oriented in several directions along short branches of a
narrow panicle. The third group has often dense panicles that have been
described in the literature as pyramidal. This term refers to an elongate
inflorescence, sometimes nodding at the tip, with at least the lower branches
arching outward or nodding, and the longest branches usually toward the
inflorescence base with progressively shorter branches toward the tip. The
heads are all or mostly oriented toward the upper side of each racemose branch.
In a few species (like S. ulmifolia), the branches tend to be relatively
widely separated along the main axis, and because the axis and branches appear
leafy, these lowest branches might be interpreted as being separate
inflorescences. Within this volume, to maintain continuity across the treatment
of Solidago, references to a pyramidal shape apply to the overall
branching pattern and disposition of heads on a single main flowering stem.
Occasional depauperate individuals with small inflorescences can cause problems
with the determination of all of the goldenrod species, but in such cases the
orientation and position of the heads relative to the branches can be helpful
in discriminating among the groups.
There are two
main forms of leaf arrangement, and collectors should be careful either to
gather the stem base as part of a specimen or to record the information on basal
leaves carefully in the field. In some species, the basal leaves are well
represented at flowering (in fact there often are few to several additional
basal rosettes in proximity to the flowering stem), the basal and adjacent
lower stem leaves the largest leaves on the plant, and the leaves gradually
reduced from the stem base toward the tip. Some authors have referred to this
leaf arrangement pattern as “basally disposed” (Cronquist 1980, 1991). In
contrast, other species have the basal leaves withered and usually absent at
flowering. The largest leaves occur from about 1/3–1/2 the way up the stem.
This leaf arrangement is sometimes referred to as “chiefly cauline”.
Some tribes of
Native Americans used goldenrods in the treatment of colds, congestion, fever,
cramps, and heart ailments (Moerman, 1998). Because they are showy when in
flower and often grow in proximity to wind-pollinated plants like ragweeds (Ambrosia,
Asteraceae) and pigweeds (Amaranthus, Amaranthaceae) that flower at the
same time of year, goldenrods have developed an undeserved reputation as
causing hay fever. However, all of the goldenrods have sticky pollen that is
dispersed by a variety of different insects. A number of species are attractive
ornamentals in the garden and are available through wildflower nurseries.
Cultivars of a few species, like S. canadensis, are more widely
available in the nursery trade. Gardeners should note that some of the most
widespread Missouri species, like S. altissima, can become very
aggressive in the garden.