16. Solidago petiolaris Aiton (downy goldenrod)
S. petiolaris var. angusta (Torr. & A.
Gray) A. Gray
S. petiolaris var. wardii (Britton) Fernald
Pl. 238 h, i;
Map 1005
Plants with the
rootstock short and sometimes branched, occasionally producing slender
rhizomes. Stems solitary or more commonly few to several, 40–150 cm long, erect
or ascending, finely ridged, sparsely to moderately pubescent with short,
curved or occasionally stiff hairs, sometimes only sparsely hairy toward the
base, not shiny, not glaucous. Leaves chiefly cauline, the largest leaves in
the lower 1/3 of the stem, the basal leaves absent at flowering. Basal and
lowermost stem leaves with the blade 6–12 cm long, 0.5–3.5 cm wide, variously 3–8
times as long as wide, narrowly elliptic-oblanceolate to elliptic or obovate,
relatively thick and stiff, angled or tapered to a sessile or short-petiolate
base, angled or more commonly short-tapered to a sharply pointed tip, the
margins entire or sparsely and shallowly toothed above the midpoint and hairy,
the surfaces sometimes sticky and somewhat shiny, the upper surface glabrous or
somewhat roughened, the undersurface glabrous, somewhat roughened, or sparsely
to moderately pubescent with minute (0.1–0.4 mm long) hairs along the main
veins, with 1 main vein, the fine, pinnate secondary veins relatively easily
observed (these usually forming an irregular network). Median and upper stem
leaves 1–15 cm long, nearly linear to narrowly obovate, otherwise similar to
the lower stem leaves. Inflorescences of axillary clusters grading into a
narrow racemose panicle, the heads oriented in several directions when short
ascending branches are present. Involucre 4.5–7.5 mm long, the bracts in 3–5
unequal series. Involucral bracts mostly narrowly oblong-lanceolate and sharply
pointed at the tip, appressed-ascending or more commonly at least the outermost
involucral bracts loosely ascending or with the tips somewhat spreading to
recurved, the thin, white to yellowish white margins hairy, the outer surface
glabrous or sparsely to moderately hairy, sometimes glandular and somewhat
sticky, with a poorly defined, green central region toward the tip, this
tapered abruptly to the midvein above or below the bract midpoint, the midvein
usually noticeably thickened. Receptacle naked. Ray florets (5–)7–9, the
corollas 3.5–7.5 mm long, yellow. Disc florets (8–)10–16, the corollas 4–5 mm
long, the lobes 0.9–1.8 mm long, yellow. Pappus 4.0–4.5 mm long, a few of the
bristles often slightly thickened toward the tip. Fruits 3–4 mm long, narrowly
obovoid, glabrous or nearly so at maturity. 2n=18, 36. May–November.
Scattered mostly
south of the Missouri River (Nebraska to New Mexico east to Illinois, North
Carolina, and Florida). Glades, bases, ledges, and tops of bluffs, openings of
mesic to dry upland forests, and savannas; also pastures and roadsides.
Steyermark
(1963) noted that this attractive species performs well in the wildflower
garden and that it is one of the earliest goldenrods to start flowering in
Missouri. The heads are relatively large for a goldenrod.
The taxonomy of
the S. petiolaris complex requires further study. On the one hand, there
are problems surrounding the distinctness of S. buckleyi from S.
petiolaris (for further discussion, see the treatment of that species).
However, there also are problems of infraspecific variation within the species.
Two elements traditionally have been accepted as occurring in Missouri
(Steyermark, 1963), but different authors have emphasized different characters
to separate the two. As noted by Steyermark (1963) and others (Cronquist,
1980), there is widespread intergradation between these phases. Plants that
have been segregated variously as var. angusta and var. wardii
have been characterized variously as having relatively narrow leaves, leaves
that are sticky and somewhat shiny, leaves with the undersurface glabrous or
slightly roughened, and/or involucres that are glabrous but with sessile
glands. In contrast, various authors have characterized var. petiolaris
as having relatively broad median and lower leaves, leaves that are not sticky
or shiny, leaves with the undersurface sparsely to moderately pubescent with
minute (0.1–0.4 mm long) hairs along the main veins, and/or involucres that are
glabrous to more commonly sparsely to moderately hairy and sometimes somewhat
sticky. The last author to study the complex was Nesom (1990d), who examined a
large suite of herbarium specimens from throughout the range of the species. He
concluded that there was no correlation in variation between any of the
aforementioned characters. Plants from the Ozarks were most likely to have
sticky, glabrescent leaves, but narrow-leaved and broad-leaved plants were
equally likely to have sticky leaves. Similarly, the pubescence of the
involucre varied independently of the leaf characters. Nesom concluded that for
the present there is no rational way to formally subdivide S. petiolaris
into varieties and that in fact a more distinctive (but still morphologically
confluent) element within the range of variation occurred not in the western
portion of the range but in a series of populations in the southeastern states.
It remains for future studies of the population genetics of the complex to
tease apart the intricate patterns of morphological variation present.