1. Plant terrestrial, or if aquatic, strongly emergent
2. Fls all unisexual; inflorescence either a dense erect spike of staminate flowers directly distal to a spike of pistillate flowers, or a group of several spheric unisexual heads attached to a zigzag main axis, spikes or heads 1–4 cm diam ..... TYPHACEAE
2' Fls bisexual or some or all unisexual; inflorescences of various types, generally < 1 cm diam if spike or head
3. Fr a berry or capsule with 3–many seeds or breaking into 1-seeded mericarps; perianth segments 4–6, well developed — actually in two whorls, but this may not be evident in open flowers
4. Lvs with expanded blades; perianth parts petal-like, white or cream ..... RUSCACEAE (Maianthemum)
4' Lvs narrowly linear; perianth parts scale-like, green to ± red or brown
5. Infl of 1–many flowers, variously clustered, subtended individually and/or in small groups by bracts; style 1, stigmas (2)3, linear, spreading; fruit a capsule ..... JUNCACEAE {G16}
5' Infl a bractless raceme; stigmas 3 or 6, ± sessile, papillate or plumose; fruit breaking into mericarps ..... JUNCAGINACEAE {G2,10,16}
3' Fr an achene or grain, 1-seeded; perianth inconspicuous or 0 or modified as ± conspicuous bristles
6. Infl a bractless emergent spike of bisexual and sometimes staminate flowers, plus 2 submerged, long-styled, sessile pistillate flowers enclosed by leaf sheath at base of peduncle; stamen 1; stigma 1 ..... JUNCAGINACEAE (Triglochin scilloides) (2) {G8}
6' Infl 1–many spikelets with flowers individually subtended or enclosed by scale-like bracts; stamens (1)3(6); stigmas 2–3
7. St leafless, the leaves all basal, sometimes reduced to bladeless sheaths ..... CYPERACEAE (2) {G2,8}
7' St at least proximally leafy
8. Sts generally 3-angled (cylindric), generally solid; nodes not swollen; leaves generally 3-ranked; spikelet generally without 2 bractlets at base that do not directly subtend flower parts; each flower subtended by 1 bract (in Carex and Kobresia a second, generally hollow, ± flask-shaped bract [perigynium] surrounds or encloses each pistillate flower); perianth of generally inconspicuous to long-exserted bristles or 0; fruit an achene ..... CYPERACEAE (2) {G2,8}
8' Sts cylindric, the internodes generally hollow; nodes swollen, knot-like; leaves 2-ranked or not in obvious ranks; each spikelet generally with 2 bractlets [glumes] at base that do not directly subtend flower parts; each flower generally enclosed by 2 additional bractlets [lemma and palea]; perianth of 2 tiny scales or 0; fruit a grain ..... POACEAE {G2,5,6,8}
1' Plant aquatic, submersed or floating
9. Plant raft-like, free-floating or stranded on shore or drying mud, either plant body 0.4–10 mm, not differentiated into stems and leaves with roots unbranched or 0, or plant with floating rosette of widely wedge-shaped, velvety-hairy leaves and many fine, branched roots ..... ARACEAE {G2,6,8,15}
9' Plant not raft-like, generally rooted, >> 1 cm, differentiated into stems and leaves, not forming floating rosettes; roots generally present, often branched; leaves linear, glabrous
10. Lvs opposite or whorled (occasionally alternate at some nodes), all cauline
11. Lf coarsely to finely toothed (teeth sometimes appearing ± 0 to naked eye); stipules 0 (leaf base may have ear-like lobes); fruit without a stiff beak ..... HYDROCHARITACEAE (Najas) {G2,8}
11' Lf entire; stipules fused to blade or free, membranous, entire; fruit with a stiff beak ..... ZANNICHELLIACEAE {G2,8,10}
10' Lvs alternate, basal and/or cauline
12. Lvs all ± basal, sheaths overlapping and blades emerging at different levels, but stem internodes very short, not evident — pistillate flowers paired, axillary, submersed, style 6–20 cm, thread-like, stigma floating, head-like; staminate and bisexual flowers in peduncled spike ..... JUNCAGINACEAE (Triglochin scilloides) (2) {G8}
12' Lvs basal and cauline or all cauline, stem internodes evident
13. Infl a dense, spheric head ..... TYPHACEAE (Sparganium) {G2,6,8}
13' Infl a spike or flowers solitary
14. Infl a flattened spike enwrapped by a sheathing bract; subtidal or intertidal seawater or brackish water of bays and estuaries ..... ZOSTERACEAE {G2,6,8}
14' Infl a cylindric spike, short- to long-stalked; freshwater, brackish, or inland saltwater habitat — carpels actually free but easily misinterpreted
15. Sepals 4; stamens 4; fruits sessile; fresh water in lakes, streams, ponds ..... POTAMOGETONACEAE {G2,10}
15' Sepals 0; stamens 2; fruits on thread-like stalks; fresh to brackish or salt water in coastal to inland areas ..... RUPPIACEAE {G2,8,10}
