1	"Plant body consisting of a jointed, hollow-stemmed central axis and whorled branches; leaves reduced to whorled scales; plant emergent"	"Equisetaceae {Equisetum}"
1	"Plant body various, but not consisting of a jointed, hollow-stemmed central axis and whorled branches; leaves various, but not whorled scales; plant free-floating, emergent, or submersed"	2
2	"Plant raft-like, free-floating on water surface or stranded along shore or in drying bottom sediments, breaking apart into individuals or small clumps"	3
2	"Plant generally anchored in bottom sediments or, if free-floating, most of plant body below water surface or not readily breaking apart --- rhizomes or stolons present or 0, sometimes elongated"	7
3	"Individual plant generally 0.4--30 mm in length or diam, sometimes not differentiated into leaves and stems; roots unbranched"	4
3	"Individual plant often >> 30 mm, differentiated into leaves and stems; roots generally branched (0 in Salviniaceae, with finely dissected, root-like submersed leaves)"	5
4	"Plant body spheric to disk-shaped or oblong, not differentiated into stems and leaves"	Araceae
4	"Plant body differentiated into a short, often branched stem with small, minutely velvety-papillate, scale-like leaves"	"Azollaceae {Azolla}"
5	"Leaf blades glossy green, glabrous, finely parallel-veined; petioles often enlarged, forming gas-filled floats"	"Pontederiaceae {Eichhornia}"
5	"Leaf blades light to dark green or +- purple, velvety-hairy, +- palmately or obscurely veined, sessile, lacking floats, +- palmately or obscurely veined"	6
6	"Leaves in floating rosettes, evidently +- palmately veined"	"Araceae {Pistia}"
6	"Leaves in whorls of 3, 2 floating, entire, obscurely veined, the 3rd submersed, finely dissected, root-like"	"Salviniaceae {Salvinia}"
7	"Leaf peltate, cordate, sagittate, or deeply notched"	8
7	"Leaf not peltate, cordate, sagittate, or deeply notched"	16
8	"Leaf peltate"	9
8	"Leaf sagittate or cordate to ovate or +- round, the base shallowly to deeply notched"	10
9	"Submersed parts not gelatinous; leaf blades generally emergent"	"Araliaceae {Hydrocotyle}"
9	"Submersed parts gelatinous; leaf blades floating"	"Cabombaceae {Brasenia}"
10	"Leaf blades pinnately veined; petioles long, stout; rhizome stout"	11
10	"Leaf blades +- palmately veined; petioles long or short, slender or stout; rhizome, if present, slender"	12
11	"Leaf sagittate; rhizome +- vertical"	"Araceae {Peltandra}"
11	"Leaf ovate to round; rhizome horizontal"	Nymphaeaceae
12	"Leaf blades palmately lobed, never sagittate, the lobes often toothed --- veinlets forming an irregular network"	"Araliaceae {Hydrocotyle}"
12	"Leaf blades ovate to cordate or sagittate, entire"	13
13	"Palmate veins 3 --- smaller veins parallel, extending from main veins toward leaf margin"	"Araceae {Peltandra}"
13	"Palmate veins generally 5--13+"	14
14	"Stipules 1--6 cm"	"Pontederiaceae {Heteranthera limosa}"
14	"Stipules 0"	15
15	"Smaller veins passing like ladder-rungs between prominent main veins"	"Alismataceae or Hydrocharitaceae"
15	"Smaller veins forming network"	"Menyanthaceae {Nymphoides}"
16	"Leaves all basal or basal and cauline on a generally erect, generally emergent stem, sometimes from rhizome or corm-like base anchored in bottom sediments"	17
16	"Leaves generally all cauline; stems emergent or taking the form of underwater or floating rhizomes or stolons that are unable to support the plant body outside of water"	47
17	"Leaves petioled, with expanded blades"	18
17	"Leaves sessile, +- linear or reduced to bladeless sheaths"	24
18	"Leaf serrate or dentate to lobed or compound"	19
18	"Leaf entire, simple"	21
19	"Leaf palmate; leaflets 4"	"Marsileaceae {Marsilea}"
19	"Leaf toothed to pinnately lobed or 1--3-pinnate"	20
20	"Leaf bases sheathing; leaves, lobes, or leaflets serrate to sharply dissected"	Apiaceae
20	"Leaf bases not sheathing; lobes or leaflets entire or dentate with +- rounded teeth"	"Brassicaceae {Nasturtium, Rorippa}"
21	"Leaves generally << 1 cm wide"	"Scrophulariaceae {Limosella}"
21	"Leaves generally >= 1 cm wide, often much larger"	22
22	"Wider leaves floating"	"Aponogetonaceae {Aponogeton distachyos}"
22	"Wider leaves generally emergent"	23
23	"Stipules 0"	Alismataceae
23	"Stipules present, 1--6 cm"	"Pontederiaceae {Heteranthera limosa}"
24	"Leaves vertically folded and attached ""edge-on"" to the stem, obviously 2-ranked"	"Juncaceae {Juncus}"
24	"Leaves cylindric, +- angled, flat, or reduced to bladeless sheaths, but not folded, not obviously 2-ranked"	25
25	"Leaves with flat blades or reduced to bladeless sheaths"	26
25	"Leaves cylindric or angled"	36
26	"Leaves bladeless or nearly so, composed mainly of a tubular sheath"	27
26	"Leaves with ordinary flat blades and generally also +- tubular sheaths"	29
27	"Stems +- triangular"	Cyperaceae
27	"Stems round, flattened, or several-angled"	28
28	"Leaf sheaths closed, forming a continuous cylinder around stem"	Cyperaceae
28	"Leaf sheaths open on one side, with overlapping margins"	"Juncaceae {Juncus}"
29	"Leaf blade with a well-developed midvein or keel"	30
29	"Leaf blade flat or rounded on back, lacking a prominent midvein or keel"	31
30	"Leaf sheaths closed, forming a continuous cylinder around stem; stem generally triangular; leaves 3-ranked"	Cyperaceae
30	"Leaf sheaths open on one side, with overlapping margins; stem round; leaves 2-ranked"	"Typhaceae {Sparganium}"
31	"Annual; leaves all basal"	"Ranunculaceae {Myosurus}"
31	"Perennial herb, or if annual, some leaves cauline"	32
32	"Plant submersed; seawater or brackish water of bays and estuaries"	Zosteraceae
32	"Plant emergent; fresh or brackish water of coastal or inland areas"	33
33	"Nodes swollen; stem generally hollow"	Poaceae
33	"Nodes not swollen; stem generally filled to center with spongy tissue"	34
34	"Leaf generally > 5 mm wide; remnants of old inflorescence a dense spike; inner surface of leaf sheaths mucilaginous"	"Typhaceae {Typha}"
34	"Leaf <= 5 mm wide; remnants of old inflorescence not evident or a raceme; inner surface of sheaths not mucilaginous"	35
35	"Leaves +- circular to semicircular in &times;-section"	"Juncaginaceae {Triglochin}"
35	"Leaves flat"	"Pontederiaceae {Heteranthera limosa}"
36	"Rhizomes and stolons 0; leaves densely tufted"	37
36	"Rhizomes or stolons present; leaves tufted or borne along rhizome or stolon"	40
37	"Leaf divided lengthwise into 4 hollow chambers; a sporangium generally embedded in adaxial base of each leaf, containing either powdery or larger spores"	"Isoetaceae {Isoetes}"
37	"Leaf solid or hollow, but not regularly divided into 4 chambers; a sporangium never embedded in leaf base"	38
38	"Plant perennial herb; leaf often with internal cross-partitions"	"Juncaceae {Juncus}"
38	"Plant annual; leaf without internal cross-partitions or partitions obscure"	39
39	"Leaf bases not sheathing"	"Brassicaceae {Subularia}"
39	"Leaf bases sheathing"	"Juncaginaceae {Triglochin}"
40	"Leaf sharply angled"	41
40	"Leaf cylindric"	42
41	"Stem triangular; leaves 3-ranked"	Cyperaceae
41	"Stem +- round; leaves 2-ranked"	"Typhaceae {Sparganium}"
42	"Leaf with internal cross-partitions"	43
42	"Leaf without internal cross-partitions"	44
43	"Leaf soft, blunt, generally <= 15 cm, loosely sheathing; cross-partitions often externally prominent"	"Apiaceae {Lilaeopsis}"
43	"Leaf generally stiff, acute, often > 15 cm, tightly sheathing; cross-partitions readily apparent by feel but often externally obscure"	"Juncaceae {Juncus}"
44	"Leaf generally >> 6 cm"	45
44	"Leaf 1--7(11) cm"	46
45	"Stem +- straight; leaf blade tip without evident terminal pore; ligule 0.5--5 mm"	"Juncaginaceae {Triglochin}"
45	"Stem zigzag; leaf blade tip with evident terminal pore; ligule 2--12 mm"	"Scheuchzeriaceae {Scheuchzeria palustris}"
46	"Plant spreading by rhizomes, producing +- spheric, ball-like structures [sporangium cases] +- 2--3 mm diam at bases of some leaves; new leaves uncoiling at tips"	"Marsileaceae {Pilularia}"
46	"Plant spreading by stolons, not producing ball-like structures at bases of leaves; new leaves not uncoiling at tips"	"Scrophulariaceae {Limosella}"
47	"Leaves (or leaf-like branches) compound or very deeply divided"	48
47	"Leaves simple, the margins entire, toothed, or shallowly lobed"	55
48	"Leaf palmately compound --- leaflets 4, floating or emergent"	"Marsileaceae {Marsilea}"
48	"Leaf pinnately compound or variously dissected"	49
49	"Leaflets lanceolate or wider; leaves mostly aerial"	50
49	"Leaflets or lobes linear, at least on submersed leaves; all or many leaves submersed"	51
50	"Leaf bases sheathing; lobes or leaflets serrate to sharply dissected"	Apiaceae
50	"Leaf bases not sheathing; lobes or leaflets entire or dentate with +- rounded teeth"	"Brassicaceae {Nasturtium, Rorippa}"
51	"Underwater parts bearing small, hollow bladders that suck in and trap small organisms when hairs at opening are triggered; plant carnivorous --- highly dissected underwater parts are actually modified stems and the bladders are the leaves"	"Lentibulariaceae {Utricularia}"
51	"Underwater parts lacking bladder-like traps; plant not carnivorous"	52
52	"Submersed leaves alternate"	"Ranunculaceae {Ranunculus}"
52	"Submersed leaves opposite or whorled"	53
53	"Submersed leaves pinnately divided, central leaf axis evident"	"Haloragaceae {Myriophyllum}"
53	"Submersed leaves palmately dissected or repeatedly forked, central leaf axis 0"	54
54	"Submersed leaves palmately dissected; floating leaves 0--few, linear-elliptic, +- entire"	"Cabombaceae {Cabomba}"
54	"Submersed leaves repeatedly forked; floating leaves 0"	"Ceratophyllaceae {Ceratophyllum demersum}"
55	"Leaves long, narrow, strap-shaped or ribbon-like, often >> 20 cm, generally at least some basal"	56
55	"Leaves linear to round, generally < 20 cm, generally all cauline"	57
56	"Plant of freshwater habitat"	"Typhaceae {Sparganium}"
56	"Plant of seawater or brackish water of bays and estuaries"	Zosteraceae
57	"Leaf with stipules or sheathing base"	58
57	"Leaf without stipules or sheathing base"	65
58	"Principal veins of leaf pinnate"	59
58	"Principal veins of leaf parallel or pinnate-parallel or only 1 leaf vein apparent"	60
59	"Leaves opposite or whorled, 2--15 mm"	Elatinaceae
59	"Leaves alternate, >> 15 mm"	Polygonaceae
60	"Leaves generally +- opposite or appearing whorled"	61
60	"Leaves generally alternate"	63
61	"Leaves emergent or floating; nodes swollen, internodes generally hollow"	Poaceae
61	"Leaves submersed or some floating; nodes generally not swollen, internodes generally solid"	62
62	"Leaves minutely toothed (teeth sometimes appearing +- 0 to naked eye); leaf base abruptly expanded, forming sheath, stipules 0"	"Hydrocharitaceae {Najas}"
62	"Leaves entire; leaf base not abruptly expanded, stipules present, free or fused to leaf base forming a sheath"	"Zannichelliaceae {Zannichellia palustris}"
63	"Stipules +- completely fused to leaf blade base"	"Ruppiaceae {Ruppia}"
63	"Stipules fused to leaf blade base <= 2/3 their length"	64
64	"Roots branched; leaves linear; midvein of leaf not differentiated from other veins; floating leaves 0"	"Pontederiaceae {Heteranthera dubia}"
64	"Roots generally unbranched; leaves linear to ovate; midvein of leaf more prominent than other veins; floating leaves often present"	Potamogetonaceae
65	"Leaves alternate"	66
65	"Leaves opposite or whorled"	69
66	"Leaves sessile; annual"	Campanulaceae
66	"Leaves petioled; per"	67
67	"Leaves toothed or lobed"	"Ranunculaceae {Ranunculus}"
67	"Leaves entire"	68
68	"Lateral leaf veins strongly diverging from midvein"	"Onagraceae {Ludwigia}"
68	"Lateral leaf veins strongly ascending to nearly parallel to midvein"	"Ranunculaceae {Ranunculus}"
69	"Leaves whorled"	70
69	"Leaves opposite"	71
70	"Leaf minutely toothed (teeth sometimes appearing +- 0 to naked eye)"	Hydrocharitaceae
70	"Leaf entire"	"Plantaginaceae {Hippuris}"
71	"Leaves fleshy"	72
71	"Leaves not or scarcely fleshy"	73
72	"Leaves 2--6 mm, linear or oblanceolate; annual; plant generally +- red"	"Crassulaceae {Crassula aquatica}"
72	"Leaves 3--50 mm linear to obovate; annual or perennial herb; plant generally not red"	"Montiaceae {Montia}"
73	"Leaves 0.5--5 mm wide"	74
73	"Leaves 6--15+ mm wide"	75
74	"Leaves minutely toothed (teeth sometimes appearing +- 0 to naked eye) to coarsely dentate, generally enlarged at base, all similar in form and submersed"	Hydrocharitaceae
74	"Leaves entire, linear to ovate, not enlarged at base, sometimes with floating distal leaves different from submersed leaves"	"Plantaginaceae {Callitriche}"
75	"Leaf veins palmate"	"Phrymaceae or Plantaginaceae"
75	"Leaf veins pinnate"	76
76	"Leaves toothed"	"Phrymaceae or Plantaginaceae"
76	"Leaves entire"	77
77	"Leaves (3)5--13 cm; stems often swollen, hollow"	"Amaranthaceae {Alternanthera}"
77	"Leaves < 5 cm; stems not swollen"	"Onagraceae {Ludwigia}"