Polygonum lapathifolium, L.

Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A., 1964, Flora Europaea - Volume 1. Lycopodiaceae to Platanaceae, Cambridge University Press : 79

26. P. lapathifolium L. , Sp. Pl. 360 (1753)

(inch P. nodosum Pers. , P. scabrum Moench and P. linicola Sutulov ).

Annual. Stems up to 80 cm, procumbent or erect, simple or branched, sometimes spotted with red. Ochreae entire or very shortly ciliate. Leaves ovate to linear-lanceolate, acute or obtuse, sometimes with a large blackish spot, glabrous or densely tomentose beneath, with pellucid, often yellow glands visible from lower surface. Spikes stout and usually dense; peduncles, and sometimes also pedicels and perianth, bearing yellow subsessile glands. Perianth duff pink or greenish-white. Nut black, glossy, usually lenticular. 2« = 22. Throughout Europe. All except Az Cr Sb.

Extremely variable, especially in habit, colour of foliar glands and of perianth, and in indumentum. The normally autogamous reproduction tends to the production of pure lines, many of which are locally constant and have therefore been named as species or subspecies; but its widespread dissemination as a weed has destroyed any geographical pattern which may have existed, and there is scarcely any correlation of these characters that remains constant over a wide area. Furthermore, it is known that some of the characters, especially of habit and tomentum, which are partly determined genetically are also very plastic phenotypically. The only variant which is known both to retain its characteristics in cultivation and to show a well-defined geographical distribution is P. brittingeri Opiz , Natural. 8: 74 (1824) (F. danubiale Kerner) which grows on river-alluvia in the basins of the upper Danube and Rhine. It has procumbent much-branched stems with very short internodes, and broadly elliptical or ovate leaves, densely tomentose beneath and with colourless glands. It probably merits recognition either as a species or as subsp. brittingeri (Opiz) Jâv. P. nodosum Pers. , Syn. Pl. 1: 440 (1805) is a commonly recur­ ring variant with glabrous leaves, yellow foliar glands, red-spotted stems, and pink flowers in a rather lax spike; it is characteristic of river-gravels in some regions. Similarly, P. tomentosum Schrank , Baier. FI. 1: 669 (1789) ( P. pallidum With. ), with a low habit, densely tomentose leaves and greenish-white flowers, is often seen on drying mud or as a weed in fields. In both cases, however, it is possible to find plants with some of these characteristics perfectly developed and others not at all, and it seems doubtful whether anything is gained by giving them taxonomic rank.