Lobed Prickly Lettuce Lactuca Serriola Asteraceae—Aster Family by Tom Reaume © 2010 Nature Manitoba Grant
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Lobed Prickly Lettuce Lactuca serriola Asteraceae—Aster family by Tom Reaume © 2010 Nature Manitoba Grant: A winter annual wildflower 20–200 cm tall with a taproot 3–25 cm long by 2–15 mm thick; along slough margins, edges of cultivated fields, roadsides, orchards and other disturbed sites; juice milky. l FLOWER HEADS pale yellow, blooming May–October; inflorescence an open panicle 15–90 cm long by 10–70 cm wide of 50–100 flower heads; floral branches 7–25, as- cending to spreading, lax at the tips, 2–60 cm long, reduced above, the longer ones with branchlets; peduncles 2–30 mm long; flower head buds 6–8 mm long by c. 3 mm wide before opening; flower heads 9–17 mm wide by 10–13 mm long, sometimes all facing the sun, opening once in the morning and wilting by evening; involucral bracts c. 17, in 3 or 4 series, imbricate, green with reddish tips, 3–13 mm long by 1.4–1.7 mm wide, the inner bracts linear and the longest at 7–13 mm, tan and spreading to descending with fruit; disc florets absent; ligulate florets perfect, 10–28; ovary c. 1 mm long, glabrous; pappi bristles 3–3.7 mm long; corolla tube white, 3–3.5 mm long with a cluster of short white curly hairs at its summit; ligules 4.5–6.5 mm long by 1.5–2.3 mm wide, a blue stripe below, apical teeth 5; stamens 5; anthers yellow, forming a tube c. 2 mm long; style yellow, hairy, exserted through the anther tube; stigma 2-parted the Upper flowering heads of Lobed Prickly Lettuce; mid- parts curled and yellow; fruiting heads white, 15–20 mm morning by a parking lot in Winnipeg, Manitoba across, with c. 18 fruit per head; flower to fruit 12–15 days. l FRUIT an achene, 1-seeded, the body tan to dark brown, tooth 2.5–3.8 mm long by c. 1 mm wide by 0.4–0.6 mm thick with 5–7 ribs on each side converging at the hairy apex; beak 2.5–4 mm by 0.05 mm thick, smooth, erect, often longer than stigma the body; pappi of white bristles, smooth, together 8–11 mm style across; receptacle 1–2.5 mm wide, hairless; seeds may germinate in late summer and the rosettes overwinter with ligule the plants flowering their second summer but dying after fruit dispersal and before the winter. anthers l LEAVES basal and stem, alternate, simple, deeply lobed to toothed to entire, clasping at least below, sessile, 3.5–25 cm long by 1–20 cm wide, reduced above, often with axil- floral lary growth; lower stem leaves with a partial twist near the branch stem exposing the dorsal (lower) side of the blade and the corolla midrib with one row of prickles 1–5 mm long (not hurtful) tube along most of its length, prickles absent on smaller leaves and near the blades’ apices, glabrous above, the margins pappus irregular with short prickles; upper stem blades mostly en- bristle tire and with fewer prickles; subtending leaves (bracts) of floral branches 0.4–20 cm long by 0.3–9.5 cm wide; auricles pointed, toothed. l STEM erect, stout, round, solid, tan to reddish green, gla- brous or some with prickles in the lower quarter; 2–20 mm ovary wide near the stiff base. Upper young plant l RANGE: (CAN) 9 provinces; (USA) 50 states; naturalized with flower head Ligulate floret x8; in North America. buds inner side ligule involucre ligulate floret Flower head 14 mm wide; below Flower head 14 mm wide; above; with Flower head 13 mm wide; below 22 ligulate florets and to the side bud upper involucral bract lower involucral bract leaf blade Nodding apex of flower head buds and a few flowers peduncle Flower head in bud x6 apex Prickles 1–5 mm long along the midrib on the under- taproot side (dorsal) of a large leaf prickly midrib 1 Young Lobed Prickly Lettuce 20 cm tall with a taproot 2 lobe Two stem leaves: (1) lower 18 cm long and outer x8 inner x4 (2) upper unlobed leaf; both in dorsal view Involucral bracts auricle Lobe margin; lobe dorsal side juice stem Cross-section through 7 midrib mm wide stem; milky juice Toothed auricles on lower at base stem leaf fruit 6 1 2 3 4 5 Left to right: (1) flower head bud 7 mm long (2) open flower head (3) wilted flower (4) fruit ripening in involucre (5) ripe fruit ready for dispersal by wind (6) fruit and pappus pappus, partial Lobed Prickly Lettuce with fruiting heads 15–20 mm wide on a calm day in Winnipeg beak seed auricle achene with ribs side thick Alternating stem leaves with toothed auricles Seed (left) and fruit (a 1-seeded achene) x12 branchlet pappi fruit involucral subtending bract leaf (bract) Fruiting head 18 mm wide before disper- Floral branch 20 cm long sal by wind Fruit (achenes) on receptacle before with flower heads in vari- spreading ous stages.