Pleurospermum (Apiaceae for Flora Nordica)

Hemicryptophyte. A hapaxanthic plant (sometimes persisting several years), to 2 m or more; taproot 15–27 mm thick. Stem hollow (also at the nodes), straight, with the primary umbel at the top of the stem; basal part 6–16 mm thick, indistinctly sulcate, not purplish, and slightly glaucous. Leaves 6–10 on the stem, the lowest one is usually the largest (basal leaves mostly withered at anthesis); sheath narrow, not clasping, not purplish; petiole 14–28 cm; blade 1–2-pinnate, 10–24 × 13–21 cm (length/width ratio 0.7–1.3). Primary leaflets 1–2 pairs; angle leaflet/rachis 35–55°; longest petiolules 0.7–3 cm. Ultimate leaflets 1-pinnatifid, with 1–2 pairs of lobes; petiolule 1.3–4.5 mm; blade 5.7–10.1(–12.5) × (4.3–)5.8–10.5 cm (length/width ratio 0.7–1.4); base shortly cuneate to truncate, rarely cordate; margin flat, minutely papillose, irregularly serrate (apical tooth 5.8–10.1 x 3.6–7.2 mm, with a length/width ratio of 1–2.2 and a hyaline tip); apices acute to acuminate.

Umbels usually slightly convex, 5–9 cm high and 13–21 cm wide; peduncle 3.5–16 cm; rays straight or slightly inwards-curved, 6–12 cm, minutely papillose on the adaxial side. Bracts 5–11, persistent, 20–85 mm, leaf-like, with an entire or pinnatifid blade. Umbellules 14–39; pedicels 1.4–2 cm, minutely papillose on the adaxial side. Bractlets (7–)10–14, persistent, 8–25 × 1.3–2.7 mm, entire or sometimes lobed; border distinctly membranous. Flowers 22–36 per umbellule, very slightly zygomorphic; sepals 0.4–1.8 mm; petals white, 2.7–3.4(–4.8) × 1.6–2.5(–3.3) mm, papillose on the back, with entire apex; filaments 2.9–4.8 mm; anthers 0.7–1.3 mm, light grey. Fruit broadly elliptic in outline, not flattened, straw-coloured; surface covered with minute, rounded papillae; carpophore divided. Mericarps 5.1–8.2 × 2.1–3.5 × 1.6–2.8 mm (length/width ratio 1.8–3); ridges 5, distinct and equally high, with an uneven, in cross section acute apex, and with an air-filled space between exocarp and endocarp; valleculae narrow, each with 1 vitta not visible on the surface; stylopodium conical to slightly flattened, 1.1–1.5 mm wide; style 1.5–3 mm, directed outwards, with a distinct, capitate stigma. – Mid-summer.

Distribution. BNem. – In Norden only known with certainty from a small area in S, around the border between Ög and Srm. S Ög Krokek and Kvillinge, Srm Kila and Björkvik (also Lunda 1877 and, up to the 1950’s, Kvarsebo). – A specimen from S Sk Smedstorp 1897 was probably mislabelled.

The first record is as late as 1853 and the species has frequently been regarded as anthropochorous, possibly spread with ley seed, or with foreign miners in the 17th or 18th century (Rydberg & Wanntorp 2001). It cannot, however, be ruled out that it is indigenous and relictual; the total area of the species shows several other disjunctions, and pollen has been found in late-Glacial deposits in southern N, eastern D and S Bl (Hultén & Fries 1986).

C Europe, reaching Poland, Estonia and NE Russia, and Siberia from the Urals to E Asia; in Siberia represented by subsp. uralense (Hoffm.) Sommier, which should possibly be regarded as a distinct species.

Habitat. Apparently favoured by humid air and mull-rich soil, often growing in or close to shady and moist stream ravines. Most localities are, however, ± heavily influenced by man: roadsides, verges of fields, formerly open ground developing into woodland. The species is sensitive to intense grazing, and an observed increase during the 20th century may be due to lowered grazing intensity; however, continued overgrowth is disfavourable, since flowering requires a good supply of light.

Biology. Although fruit production is fairly high in the Swedish populations, experiments showed that the rate of germination was very low (Horn af Rantzien 1946). However, the conditions during these experiments were perhaps not optimal, or the fruit may need a more or less long resting period before germination.