1	"Flowers at anthesis 2.5-5 mm long"	2
1	"Flowers 5-25 mm long"	4
2	"Pedicels 10-50 mm long"	"Lobelia dioica"
2	"Pedicels 2-8 mm long"	3
3	"Hypanthium densely hairy"	"Lobelia darlingensis"
3	"Hypanthium glabrous"	"Lobelia fenshamii"
4	"Flowers in terminal raceme, subtended by bracts or very reduced leaves"	5
4	"Flowers solitary in the axils of full-sized leaves"	9
5	"Leaves 8-20 times longer than broad; petioles absent"	6
5	"Leaves 1-4 times longer than broad, petiolate"	7
6	"Longest corolla lobe 12-17 mm long; leaves 0.4-1(-1.6) mm wide, entire, recurved to revolute; upper corolla lobes glabrous or with a few minute hairs at very apex"	"Lobelia gibbosa"
6	"Longest corolla lobe 3-8 mm long; leaves 1.3-6 mm wide, toothed, flat; upper corolla lobes with conspicuous hairs 0.2-0.3 mm long at distal end"	"Lobelia browniana"
7	"Leaves with crenate margins and cordate base; leaves and stems hairy; pedicels 3-7 mm long"	"Lobelia trigonocaulis"
7	"Leaf margins serrate or pinnatifid, base cuneate; leaves and stems glabrous; pedicels 10-20 mm long"	8
8	"Lowest lobe of corolla more or less circular"	"Lobelia andrewsii"
8	"Lowest lobe of corolla spathulate, more than twice as long as wide"	"Lobelia dentata"
9	"Plants semi-aquatic; leaves entire"	"Lobelia fontana"
9	"Plants terrestrial; leaves toothed"	10
10	"Leaves broadly ovate to orbicular, 1-1.8 times longer than broad"	11
10	"Leaves linear to elliptic, 1.8-20 times longer than broad"	14
11	"Leaves with 3-6(-7) pairs of teeth; stems and leaves glabrous"	12
11	"Leaves with 6-12 pairs of teeth; stems and leaves at least sparsely hairy on new growth, and often conspicuously hairy"	13
12	"Larger leaves 7-15 mm long, green underneath; flowers blue"	"Lobelia quadrangularis"
12	"Larger leaves 16-30 mm long, often purplish underneath; flowers white"	"Lobelia purpurascens"
13	"Anther tube 1.5-1.7 mm long, with sparse hairs 0.05-0.15 mm long"	"Lobelia arnhemiaca"
13	"Anther tube 1.8-2.3 mm long, with dense hairs 0.3-0.45 mm long"	"Lobelia membranacea"
14	"Hypanthium and pedicel densely hairy"	"Lobelia leucotos"
14	"Hypanthium and pedicel glabrous"	15
15	"Stems winged; growing on littoral zone"	"Lobelia anceps"
15	"Stems not winged; growing away from littoral zone"	16
16	"Leaves 5-25 times longer than wide"	17
16	"Leaves 1.8-5 times longer than wide"	18
17	"Anther tube with white hairs in upper half; calyx lobes 2-4 mm long; corolla lobes all about equal in width"	"Lobelia douglasiana"
17	"Anther tube glabrous; calyx lobes 1-2.2 mm long; upper corolla lobes less than half width of lower lobes"	"Lobelia stenophylla"
18	"Leaves broadest near the base, with 7-12 pairs of teeth, always green below; all corolla lobes about the same width"	"Lobelia concolor"
18	"Leaves broadest near the middle, with 4-6(-7) pairs of teeth, often purplish below; upper corolla lobes much narrower than lower"	"Lobelia purpurascens"