Annuals, 1–13+ cm. Stems 1, decumbent to erect (straight), glabrous. Leaves ± fleshy, margins entire, eciliate, apices obtuse, faces glabrous; basal deciduous at bolting, petiolate, blades oblanceolate 44–50 × 5–7 mm [cult.], bases attenuate; proximal cauline and some distal withering by flowering; cauline sessile, blades linear-lanceolate to spatulate, 15–55 × 1–4 mm, reduced distally, bases cuneate; distal sessile, blades linear-lanceolate to spatulate. Heads (disciform) in ± densely paniculiform arrays. Peduncles glabrous, bracts linear. Involucres campanulate, 5–8+mm. Phyllaries in 3–4 series, lanceolate, subequal, bases scarious, margins eciliate, green zones foliaceous (outer), apices obtuse, faces glabrous. Ray florets 0. Pistillate florets 14–47+ in 2–3+ series; laminae 0 (corolla tubes 2–2.4 mm, shorter than style branches). Disc florets 5–8+; corollas yellow, 3.1–3.9 mm, lobes deltate to triangular, 0.2–0.3 mm. Cypselae purple, obovoid, ± compressed, 2.8–2.9 mm, 2–4-nerved, faces strigillose; pappi white to yellowish white, 4.8–5.2 mm. 2n = 14.
Phenology: Flowering Aug–Sep.
Habitat: Brackish sand and mud, intertidal salt marshes, moist dune slacks
Elevation: 0 m
N.B., P.E.I., Que.
Of conservation concern.
Symphyotrichum laurentianum is known only from the southern shores of the Gulf of St. Lawrence.