A number of species are cultivated, and additional ones may escape besides those included below. Campanula is clearly an unnatural assemblage, even with the distinctive Campanulastrum removed (Haberle et al. 2009), but a division into smaller, monophyletic genera is not yet attainable.
1. Corolla ca. (2.5–) 3.5–5.5 cm long.
2. Calyx with large reflexed appendages at the base of the lobes; stigmas 5; biennial.
2. Calyx without appendages; stigmas 3; perennial.
1. Corolla less than 3 (–3.5) cm long.
3. Plant lax, the weak 3-angled stem and leaves retrorsely scabrous, clinging to other plants; corolla (4–) 5.5–10 (–11) mm long, the lobes longer than the tube; leaves all less than 7 (very rarely 8) mm wide; moist or wet habitat.
3. Plant (at least flowering stems) ± erect, the stem and leaves smooth (or if scabrous, not retrorsely so); corolla (9–) 12–30 (–35) mm long, the lobes shorter than the tube; leaves various; usually of dry or rocky habitat.
4. Ovary glabrous (very rarely puberulent); cauline leaves obscurely if at all petiolate, linear to narrowly lanceolate and entire to weakly denticulate at middle of stem, ranging to lanceolate, oblanceolate, or rotund and coarsely toothed at the base of the stem.
5. Capsules opening by pores near the summit; corollas (18–) 22–30 (–35) mm long; middle and upper cauline leaves sparsely denticulate; basal leaves oblanceolate; rarely escaped from cultivation.
5. Capsules opening by pores near the base; corollas (9–) 12–22 (–24) mm long; middle and upper cauline leaves entire; basal and juvenile leaves (often absent) suborbicular, ovate, or even deltoid; common native.
4. Ovary spreading-pubescent or retrorse-hispidulous (rarely glabrous); cauline leaves distinctly petioled toward lower part of stem, regularly to irregularly crenate to sharply toothed, lanceolate to ovate or deltoid at middle of stem, ± cordate.
6. Flowers all or mostly crowded in a terminal cluster.
6. Flowers solitary or in an elongate or open inflorescence.
7. Plant completely glabrous; corolla spreading or flaring.
7. Plant pubescent, at least on ovaries and/or petioles; corolla bell-shaped but with sides ± parallel.
8. Flowers nodding; calyx lobes usually spreading-reflexed at maturity; ovary retrorse-hispidulous (hairs less than 0.3 mm long), rarely glabrous.
8. Flowers erect or ascending; calyx lobes erect into maturity; ovary bristly with ± spreading hairs more than 0.5 mm long.