Key to Wisconsin Campanula
- 1a.Flowers on long, slender pedicels, solitary or up to 15 in a diffuse raceme or panicle; corollas (9–) 12–22 (–24) mm long; upper leaves linear to narrowly lanceolate, the margins entire; calyx and outer surface of unexpanded corolla glabrous C. rotundifolia
- 1b.Flowers numerous, in clusters or terminal spikes, racemes, or thyrses; corollas 20–35 mm long; upper leaves ovate to oblong, lanceolate, or narrowly triangular, crenate, denticulate, or serrate; calyx and outer surface of unexpanded corolla pubescent 2
- 2a.Flowers sessile or subsessile, all or mostly crowded in upper axils, forming a leafy-bracted, head-like cluster; leaves denticulate, hirtellous; ovary smooth; basal leaves lanceolate to ovate-oblong C. glomerata
- 2b.Flowers short-pedicellate; leaves serrate to coarsely serrate; ovaries pubescent; basal leaves reniform to cordate or broadly ovate
- 3a.Flowers erect or ascending (but capsule pendent), (1–) 2–4 in loose, terminal and axillary clusters; leaves short-bristly; ovary bristly with pale, spreading hairs ˃ 0.5 mm long; calyx segments remaining erect into maturity C. trachelium
- 3b.Flowers nodding, solitary at each node in ± dense, secund racemes; leaves glabrous above, usually scabrid on the margins and veins beneath; ovary nearly glabrous to finely retrorse-strigose with hairs ˂ 0.3 mm long; calyx teeth loosely deflexed at anthesis C. rapunculoides
As currently circumscribed, Campanula is regarded as an unnatural group (Roquet et al., 2008; Haberle et al., 2009; Mansion et al., 2012). Apart from Campanulastrum, relationships within the rest of the bellflowers are not well understood, but a number of recent phylogenetic studies have clarified clades within the subfamily Campanuloideae, inducing Morin (2020) to pursue a modern classification system for North American species by proposing smaller, monophyletic genera. Species of Campanula popular as garden ornamentals include C. carpatica (Carpathian bellflower), C. persicifolia (peach-leaved bellflower), C. poscharskyana (Serbian Bellflower), and C. portenschlagiana (Dalmatian Bellflower), but none has yet been found as an escape.