1 | Inflorescences of pedunculate heads, at least some peduncles more than 1 cm; largest leaves generally more than 5 cm long |
1' | Inflorescences of sessile heads, or heads on a peduncle less than 1 cm; largest leaves often less than 5 cm long |
2 | Terrestrial; stems solid, not rooting at nodes; leaves pubescent; bracteoles longer than tepals, with a prominently raised central vein, pubescent on back; peduncles 2-16 cm long; tepals 3.0-4.3 mm long, appressed-puberulent |
2' | Aquatic; stems hollow, often rooting at lower nodes; leaves glabrous or glabrate; bracteoles much shorter than tepals, without prominently raised central vein, glabrous; peduncles 1.0-5.5 cm; tepals 5-6 mm long, glabrous |
3 | Plants always rooting at lower nodes; stems pubescent in 2 lines; bracts and bracteoles less to 0.8 mm long; perianth glabrous; tepals to 2 mm long; stamens usually 3 |
3' | Plants sometimes rooting at lower nodes; stems sometimes pubescent in 2 lines; bracts and bracteoles more than 1 mm long; perianth pubescent, at least below; tepals more than 2.5 mm long; stamens 5 |
4 | Plants not rooting at nodes; densely velutinous, especially on young stems and undersurface of leaves; largest heads often more than 8 mm long; bracts, bracteoles and tepals erect; tepals 2.6-5 mm long |
4' | Plants rooting at nodes; glabrescent, velutinous only when young; heads less than 8 mm long; bracts, bracteoles and tepals spreading; tepals 3.7-4.5 mm long |