Proc. Amer. Acad. Arts 6: 543. 1865.
Plants 30–130 cm; caudices short, woody. Stems 1–10+, ascending-erect, glabrous, sometimes sparsely strigose in arrays. Leaves: sometimes rosettes of smaller leaves present at flowering; basal and proximal cauline tapering to elongate, winged petioles, bases nearly sheathing stems, blades linear-lanceolate, 50–200 (including petiole) × 4–9 mm, reduced distally, margins entire, apices acute, faces glabrous; mid and distal cauline sessile, blades linear, 25–100 × 3–7 mm, reduced distally and sometimes scalelike, margins entire. Heads 15–190, in racemiform to narrowly paniculiform arrays, rarely slightly secund, 12–45 × 2–11 cm, branches ascending. Peduncles 3–8 mm, glabrous or glabrate; bracteoles 3–6, grading into phyllaries. Involucres campanulate, 2.5–4 mm. Phyllaries in 3–4 series, linear-triangular, outer 1/3–1/2 length of inner, 1–3 × 0.4–0.9 mm, unequal, margins involute apically, midribs usually enlarged and translucent, inner with margins involute, apices sharply acute. Ray-florets 8–10; laminae 1.2–2.5 × ca. 0.75 mm. Disc-florets 10–21; corollas 2.8–4 mm, lobes 1 mm. Cypselae (obconic) 1–1.5 mm (4–7 ribs lighter than body), sparsely to moderately strigose; pappi 1.5–2 mm. 2n = 18.
Phenology: Flowering Aug–Oct.
Habitat: Near streams in asbestos-laden soils
Elevation: 600–900 m
Solidago guiradonis is a rare species found only in the vicinity of San Carlos and San Benito peaks, San Benito and Fresno counties, California. It is similar to S. confinis but has much narrower leaves and smaller cypselae.
"/3lengthofinner,1-3×0.4-0.9mm,unequal,marginsinvoluteapically,midribsusuallyenlargedandtranslucent,innermarginswithmarginsinvolute,apices" is not declared as a valid unit of measurement for this property.