1	"Plants not reduced, clearly differentiated into stems, leaves; floating aquatics or not; inflorescence a spike, conspicuous; perianth parts 0, 4, 6; stamens 0, 2, 3, 4, 6 (genera treated as Araceae in TJM (1993), minus <i>Acorus</i>)"	2
1	"Plants much reduced, not differentiated into stems, leaves; floating aquatics; inflorescence 1-flowered, inconspicuous; perianth parts 0; stamens 1, 2 (genera treated as Lemnaceae in TJM (1993))"	6
2	"Plant aquatic, floating; inflorescence +- sessile, inconspicuous among basal leaves"	"Pistia {Pistia stratiotes}"
2	"Plant terrestrial or near edge of water; inflorescence peduncled, +- conspicuous"	3
3	"Petiole < leaf blade; inflorescence bract yellow"	"Lysichiton {Lysichiton americanus}"
3	"Petiole +- >= leaf blade; inflorescence bract sometimes pale yellow-green but not yellow"	4
4	"Peduncle +- >= leaf; inflorescence bract white both surfaces (tip generally pale green)"	"Zantedeschia {Zantedeschia aethiopica}"
4	"Peduncle generally << leaf; inflorescence bract abaxially pale yellow-green, adaxially +- white to pale yellow-green or dark purple, or green both surfaces (margins pale green to white or not)"	5
5	"Inflorescence sterile in +- upper 1/2, flowers only in lower 1/2; inflorescence bract abaxially pale yellow-green, adaxially +- white to pale yellow-green or dark purple"	Arum
5	"Inflorescence fertile throughout; inflorescence bract green both surfaces (margins pale green to white or not)"	"Peltandra virginica"
6	"Roots 0 (see also <i>Lemna trisulca</i>)"	7
6	"Roots present"	8
7	"Plant body +- cylindric to nearly spheric, 0.4--1.3 mm"	Wolffia
7	"Plant body flat, linear to oblong, 3--10 mm"	Wolffiella
8	"Root generally 1"	Lemna
8	"Roots generally 2--16"	9
9	"Roots generally 2--7; plant body 3--5 mm, veins 3--7; winter buds 0"	"Landoltia {Landoltia punctata}"
9	"Roots generally 7--16; plant body 5--10 mm, veins 7--12; winter buds produced"	"Spirodela {Spirodela polyrhiza}"