Calystegia R. Br.

Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A., 1972, Flora Europaea. Volume 3. Diapensiacea to Myoporaceae, Cambridge: Cambridge University Press : 78

4. Calystegia R. Br. 2

Perennial rhizomatous herbs; stem procumbent or climbing. White latex present. Leaves petiolate, variously lobed at the base. Flowers solitary, axillary, with a pair of large and sometimes inflated bracteoles partly or entirely concealing the sepals. Corolla large, infundibuliform or tubiform, glabrous or ciliate. Ovary glabrous, unilocular; ovules 4. Stigma bilobed; lobes swollen and elongate. Pollen grains pantoporate; exine more or less smooth.

The genus differs constantly from Convolvulus in its pollen grains and unilocular ovary, but the European species are most easily distinguished by the pair of broad bracteoles immediately below the sepals. The generic delimitation is discussed by W. H. Lewis &R. L. Oliver, Ann. Missouri Bot. Gard. 52: 217-222(1965). A flore pieno cultivar of C. pubescens Lindley , from China, easily recognized by its pink flowers and oblong-hastate leaves, is widely cultivated and has sometimes persisted as a garden escape. Hybrids may become well established by vegetative reproduc­ tion. White-flowered plants from S. Sweden which have been referred to 3 are probably 2(a) x 4; and glabrous pink-flowered plants with saccate bracteoles and a rounded leaf-sinus, well established in C. England (Nottinghamshire), may be 3 x 4. 2(a) x 3 (C. x lucana (Ten.) G. Don) may be widespread in S. Europe and in the British Isles, but is often difficult to distinguish from one or other parent.

1 Stems not or weakly twisting, procumbent; leaves reniform

1. soldanella

1 Stems strongly twisting and climbing; leaves not reniform 2 Corolla white (occasionally the centre-band only of each lobe ± pinkish)

3 Bracteoles rarely more than 15 mm wide, not overlapping, flat or keeled at the base; corolla usually not more than 50 mm; stamens not more than 23(-25) mm 2. sepium

3 Bracteoles. 15-40 mm wide when flattened, overlapping, ±saccate at the base; corolla 50-90 mm; stamens 24-37Ç-40) mm 3. silvatica

2 Corolla pink

4 Bracteoles not or scarcely overlapping, acute or somewhat rounded at the apex, flat or keeled at the base; leaf-sinus acute or rounded, with divergent sides 2. sepium

4 Bracteoles overlapping, obtuse to emarginate at the apex, ±saccate at the base; leaf-sinus oblong 4. pulchra