Smooth elm-leaf goldenrod

Solidago microphylla Engelmann ex Small; S. ulmifolia Muhlenberg ex Willdenow var. microphylla A. Gray

Plants 40–120 cm; caudices compact, branching, woody. Stems 1–10+, essentially glabrous. Leaves: basal and proximal cauline tapering to short petioles, blades oblanceolate, 50–70 × 10–20 mm, margins serrate, scabroso-strigose, apices acute to acuminate, faces glabrous; mid and distal cauline subpetiolate or sessile, blades elliptic-lanceolate, 30–70 × 7–15 mm, gradually reduced distally, tapering to bases, margins serrate, scabroso-strigose; branch leaves similar, reduced to bracts distally. Heads 160–480 in paniculiform arrays, with a strongly secund, primary, arching axis and nearly always 4–5(–8) leafy, elongate, arching, secund, proximal branches. Peduncles 2–5 mm, bracteolate, glabrous; bracteoles grading into phyllaries. Involucres narrowly campanulate, 3–5 mm. Phyllaries in 3–4 series, linear-lanceolate, strongly unequal, acute to ± attenuate, glabrous. Ray florets 1–4; laminae 1–2 × 0.5–0.8 mm. Disc florets 4–6; corollas 2.5 mm, lobes 1 mm. Cypselae 1.5–2 mm (6–9 ribs), sparsely strigose, more so apically; pappi 1.5–2 mm. 2n = 18.

Flowering Aug–Oct. Sandy and alluvial soils, dry open woods, banks of shaded creeks; 40–300 m; Ark., Kans., Okla., Tex.

Solidago delicatula is similar to S. ulmifolia, but is essentially glabrous (except for leaf margins) with smaller, more numerous, less conspicuously veiny leaves. It is sufficiently distinct from S. ulmifolia that inclusion in that species as var. microphylla does not appear warranted. Reports from Alabama, western Florida, Louisiana, and Mississippi are likely just smaller-leaved S. ulmifolia. Solidago helleri Small may be a hybrid between S. delicatula and S. ulmifolia.