Description from Flora of China
Roots tuberous, ovoid-globose or ovoid, 2.5-5 × 1-1.5 cm. Stems twining, usually with a few branches, up to more than 1 m, glabrous. Leaves alternate or sometimes opposite, evenly distributed along stems; petiole absent or to 22 mm; blade linear-lanceolate to ovate or deltoid, 2-10 × 0.4-3.5 cm, base cuneate, rounded, truncate, or cordate, margin entire, subentire, sinuous-crenate, or serrate, apex obtuse, acute, or acuminate. Flowers solitary, terminal on main stems and branches; pedicels 2-12 cm, glabrous. Calyx tube adnate to ovary up to top, obconical, 3-7 × 4-10 mm, glabrous, 10-ribbed; lobes narrowly triangular-lanceolate, 4-11 × 1-5 mm, glabrous, margin entire, apex acuminate or acute; sinus between lobes narrow, pointed or slightly obtuse. Corolla pale blue or blue-purple, rotate, 5-fid to near base; lobes elliptic, 1-3.5 × 0.6-1.2 cm, apex acute. Filaments slightly dilated and ciliate at base, 1-3 mm; anthers 4-5 mm. Superior part of capsule broadly conical, valves ca. 4 mm; inferior part obconical, 10-16 × ca. 8 mm. Seeds numerous, brown-yellow, oblong, ca. 1.5 mm, wingless. Fl. and fr. Jul-Oct.
Two of us (Lammers and Klein) do not agree with the broad treatment of Codonopsis convolvulacea adopted here, i.e., with C. forrestii, C. grey-wilsonii, and C. vinciflora treated as subspecies of C. convolvulacea, with C. limprichtii, C. efilamentosa, and C. mairei included in the synonymy of C. convolvulacea subsp. forrestii, and with C. limprichtii var. pinifolia included in the synonymy of C. graminifolia. Instead, based on our analysis of herbarium material including types, we recognize seven morphologically discrete entities. The nature of the differences distinguishing them suggests each is reproductively isolated from the others and so we treat them as species: C. convolvulacea (including C. forrestii var. heterophylla), C. efilamentosa, C. forrestii (including C. forrestii var. hirsuta), C. grey-wilsonii, C. limprichtii (including C. graminifolia and C. limprichtii var. pinifolia), C. mairei (including C. retroserrata), and C. vinciflora. We also recognize an eighth species, C. macrophylla Lammers & L. L. Klein, known only in cultivation but believed to be from Xizang. See Lammers and Klein (Bot. Stud. (Taipei) 51: 553-561. 2010). However, one of us (Hong) notes that the taxonomy of this complex has been extremely controversial in the past, with several different classifications having been proposed. Based on critical examination of all available specimens in BM, E, K, KUN, and PE and recent field observations in S and SE Xizang and NW Yunnan, the C. convolvulacea complex is found to be extremely variable, particularly in the length of the petioles and in the shape, texture, and margin of the leaf blades. Some characters, e.g., shape of leaf blade, are merely a polymorphism within populations, and the characters distinguishing C. convolvulacea, C. forrestii, C. grey-wilsonii, and C. vinciflora are variable within geographic regions but are not distinct.
Forests, open woods, forest margins, thickets, grassy slopes, pastures, meadows; 1000-4600 m. W Guizhou, SW Sichuan, S and SE Xizang, Yunnan [Bhutan, N Myanmar, Nepal].