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Sium latifolium L. map
Linnaeus, Sp. pl.: 251 (1753). – Type: Clifford Herbarium 98, Sium 1 (BM) lectotype, sel. by Reduron & Jarvis, Regnum Veg. 127: 89 (1993).
D Bredbladet Mærke. F sorsanputki. N stor vasskjeks. S vattenmärke.
Helophyte. Glabrous, frequently heterophyllous perennial, to 130 cm; rhizome short, ± horizontal, 5–11 mm thick. Stem hollow; basal part 8–16 mm thick, sulcate, usually slightly purplish, ± glaucous; upper internodes sulcate. Leaves 6–8 on the stem and 1–2 at the base (the lowermost stem leaves are usually the largest); at least cauline leaves usually aerial and broad-lobed, lower submerged ones usually narrow-lobed, but intermediate, variously lobed basal leaves common. Aerial leaves broad-lobed, 1-pinnate, with 3–8 pairs of normal leaflets (rudimentary or completely reduced leaflets on the 2–4(–5) proximal nodes); sheath 2–5 cm long, rather broad, not inflated; petiole (8–)13–25(–35) cm (measured up to the first normal leaflets); blade 14–30 × 5.5–15(–20) cm (length/width ratio1.4–2.9); angle leaflet/rachis 35–70°. Apical leaflet lanceolate to narrowly elliptic; petiolule 6–28 mm; blade (33–)43–88(–105) × (9–)13–33 mm, with a length/width ratio of 2.1–3.8(–4.7); base cuneate to rounded (rarely cordate); apex obtuse to acute, fairly short tapering; margin serrate with usually purplish-tipped, acuminate teeth. Lateral leaflets similar to the apical one but sessile; blade 52–111 × (10–)14–34 mm, with a length/width ratio of 2.5–4.5(–6.1). Submerged leaves narrow-lobed, 4–5-pinnatifid; petiole rather thick; ultimate lobes 2–4(–8) mm long, usually narrower than 1 mm, gradually tapering to an acute apex.
Umbels convex, 3.5–6 cm high and 9–15 cm wide; peduncle 5–14 cm; rays straight or slightly bent inwards, 3.2–6.3 cm, glabrous. Bracts (3–)6–12(–14), persistent, often united at base, 12–23(–33) × 1–4.5(–6) mm, entire or serrate, with a distinct membranous border. Umbellules (11 –)19–35(–53); pedicels 0.9–1.4 cm, glabrous. Bractlets 5–12, persistent, 4.5–9(–13.5) × 0.8–1.6(–2.2) mm (very different in size), usually entire, distinctly membrane-bordered. Flowers not zygomorphic, (16–)29–38(–47) per umbellule; sepals lanceolate, persistent, 0.4–1 mm; petals white, 1.2–1.8 × 1–1.5 mm, emarginate (apical cut 0.1–0.4 mm deep); filaments 1.6–2.5 mm; anthers usually violet, 0.4–0.5(–0.6) mm. Fruit elliptic to obovate in outline; carpophore usually not developed. Mericarps (2.7–)3.1–4 × 1.1–1.5 × 1–1.4 mm (length/width ratio 2.5–3.1); primary ridges whitish, high and wide, rounded, with large, air-filled cavities; valleculae narrow; vittae numerous, surrounding the endocarp (visible on the surface); stylopodium conical, 0.5–0.8 mm wide; style 1–1.8 mm, directed outwards or deflexed. – Mid-summer to late summer.
2n=20 (S Sk 2); 2n=22 + 0–2B (S Sk). – [2n=20]
Distribution. Nem–BNem. D common on the eastern islands, in Jylland scattered to rare (although locally fairly common). S common to rather common in most of the southern lowlands (but rare in Hl, eastern Bl and middle Klm), reaching southern BhG, Dls and Vrm (the shores of Vänern), southern and eastern Vsm, southeastermost Dlr (Folkärna) and southern Gst; escaped from cultivation in Gtl Hejde 1880’s. F EK Hamina (lower course and mouth of Summajoki), elsewhere probably extinct; formerly known from V several places along River Sirppujoki (Männäistenjoki) in the northwestern part of the province (last seen in Uusikaupunki 1972), ES Parikkala (Siikalahti); probably only casual in U (Kirkkonummi 1913, and Hanko late 1980’s). – Specimens from N Vf Ramnes 1931, F St Kiikoinen 1933, EH Vesilahti 1898, PS Heinävesi 1903 and PK Tohmajärvi 1910 are probably mislabeled; there are unconfirmed records from F V Rymättylä 1877, 1899 and U Kirkkonummi 1907, 1981.
Temperate Europe, W and C Siberia.
Habitat. Shallow, nutrient-rich, still or slow-flowing freshwaters with clay- or mud-bottom, in full sun or half-shade; lakes and slow streams as well as ditches and pools, marl-pits and alder carrs.
Biology. Perhaps poisonous. – The fruits have large, air-filled cavities in the ridges and can float for at least ten days (Egholm 1951). In Finland, the seed production is usually fairly high, and there is fairly great annual variation in the number of individuals in small colonies (Rintanen & Kare 2000).
Similar taxa. Sium latifolium is similar to Berula erecta, but B. erecta has only normal leaflets or 1 reduced pair (2–5 pairs vestigial in S. latifolium), its apical leaflets are wider and lobed, and the peduncles shorter than 4 cm. – Cicuta virosa has sometimes 1-pinnate leaves, but the stem is terete, and the umbels usually lack bracts.
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