Silaum silaus (L.) Schinz & Thell. map ill
Schinz & Thellung, Vierteljahrsschr. Naturf. Ges. Zürich 60: 359 (1915). – Peucedanum silaus L., Sp. pl.: 246 (1753). – Type: Burser Herbarium VIII: 73 (UPS) lectotype, sel. by Reduron, Nord. J. Bot. 22: 84 (2002).
Silaus flavescens Bernh. (1800).
Silaus pratensis Bess. (1820).
D Peberskærm. F lännenketunputki. N engkjeks. S ängssilja.
Literature. Nilsson & Gustavsson 1977.
Hemicryptophyte (perennial). To (70–)110 cm, with an indistinct aromatic scent; taproot 5–15 mm thick. Stem solid; basal part 3–6 mm thick, terete to angular, usually indistinctly purplish, not or sometimes slightly glaucous; upper internodes angular to sulcate, sometimes indistinctly winged. Leaves 1–4 at the base and 4–7 on the stem, one of the basal or the lowest stem leaf is the largest; sheath rather narrow, occasionally purplish; petiole 7.5–18.5(–24) cm; blade 2(–3)-pinnate, 11–32 × 9–20 cm (length/width ratio 1.1–1.5). Primary leaflets 4–7 pairs; angle leaflet/rachis 25–45(–60°); longest petiolules 1.4–6(–8.1) cm. Ultimate leaflets 2-pinnatifid, with 2–3(–5) pairs of lobes; petiolule 10–28 mm; blade 19–46 × 16–34(–42) mm, with a length/width ratio of 1–1.6(–2.1); base shortly attenuate to cordate; margins not folded, distinctly papillose. Ultimate lobes 9–22 × 1.8–5.5 mm (length/width ratio (2.4–)3.2–7.6); apices acute to acuminate, usually with distinctly purplish tips.
Umbels flat, 4–5 cm high and 8–9 cm wide; peduncle 6–19 cm; rays straight, 3.1–6 cm (unequal in length), glabrous or indistinctly papillose of the at the base. Bracts 0(–2). Umbellules 8–13; pedicels 6–8 mm, glabrous or indistinctly papillose on the adaxial side. Bractlets 8–12, persistent, 2.5–4.5 × 0.4–0.8 mm; border indistinctly membranous. Flowers 16–26 per umbellule, not or slightly zygomorphic; sepals absent (or indistinct, up to 0.2 mm); petals 1–1.4 × 0.7–1 mm, emarginate (apical cut 0.1 mm deep); filaments 1.2–2(–3.3) mm; anthers 0.4–0.5(–0.7) mm. Fruit elliptic to oblong in outline, straw-coloured to red-brown. Mericarps 3.2–4.7 × 1.7–1.9 × 0.8–1.2 mm (length/width ratio 2.2–2.5); ridges in cross section equally high; stylopodium conical, 0.5–0.7 mm wide; style 0.8–1.1 mm, directed outwards or deflexed. – Mid-summer to late summer.
Distribution and habitat. First Nordic record S Sk 1805; according to Lilja (1838) growing in seminatural habitats, often in boundary zones (meadows, verges of fields and roads), and thus probably archaeophytic or even indigenous. Elsewhere a late, mostly casual alien. – D LFM established in Bonnet Skov (first find 1982 as “Pomle, Rørmosen”, in drainage ditch); Sjæ Søndersø 1947–51 (thicket), Ørby 1981 (grassland), ØJy Tvilum 1969. S Sk Östra Vemmenhög, declining; earlier also Skivarp (until 1935) and Malmö (Rosenlund until 1874, Stora Mölleberga 1906). F casual in EP Vaasa 1947–55 (introduced with German transports during 2nd World War; Luther 1948).
W, C and SE Europe (perhaps also SW Siberia, where it merges with the eastern S. alpestre).
Variation. Very variable in shape of leaf-lobes, even among the collections from S Sk. However, the ultimate leaflets are almost always deeply lobed with ± entire lobes, and they have distinctly papillose margins. The specimens from F EP have slightly larger and more divided leaves, and perhaps slightly paler flowers with longer filaments (2.3–3.3 mm) and slightly longer anthers (0.6–0.7 mm); the provenance of that population is uncertain.
Similar taxa. Narrow-lobed specimens of Silaum silaus are sometimes confused with Selinum carvifolia, but S. carvifolia differs in stems (distinctly winged in upper part), umbels (rays distinctly papillose, usually more than 20), petals (white) and fruits (not elongated, and the mericarps have lateral wings that are wider than the median ones). – See also S. alpestre (rare casual).