1 Stamens 3, filaments connate into a column 0.1-0.15 mm long; fruiting pedicels thicker and often also shorter, spreading in fruit; seeds variously ribbed or striate.

  2 Perennial herbs; stipules of main stems dark brown, auriculate; capsules 1.7-1.9 mm in diameter; seeds 0.8-0.9 mm long; [subgenus Moeroris]

  2 Annual herbs; stipules of main stems pale green to pale brown, not auriculate; capsules 1.9-2.7 mm in diameter; seeds 0.9-1.5 mm long.

    3 Inflorescences near tips of branchlets of solitary pistillate flowers.

      4 Pistillate nectaries subentire; styles ± appressed; ultimate branchlets smooth or essentially so; main stems not conspicuously angled; leaf apices acute to narrowly obtuse; [subgenus Moeroris]

      4 Pistillate nectaries deeply 6-9-lobed; styles ascending to erect; ultimate branchlets scabridulous; stems usually angled; leaf apices rounded; [subgenus Swartziani]

    3 Inflorescences near tips of branchlets of 1 pistillate flower and 1-3 staminate flowers; [subgenus Swartziani].

        5 Pistillate nectary annular, 5-7-lobed; staminate sepals 5 (-6); capsules 1.9-2.1 mm in diameter; seeds 0.9-1 mm long

        5 Pistillate nectary of 3 glands; staminate sepals 5-6 in flowers of basal cymules, 4 in flowers of distal cymules; capsules 2.3-2.7 mm in diameter; seeds 1.1-1.5 mm long.

          6 Pistillate nectary glands subequal, reniform, broader than long; leaf blades densely scabridulous on both surfaces; bisexual cymules with 1-3 staminate flowers

          6 Pistillate nectary glands strongly unequal, spatulate, as long as or longer than broad; leaf blades glabrous on both surfaces or sparsely to moderately scabridulous abaxially; bisexual cymules with 1 staminate flower.

             7 Lower cymules with 2 staminate flowers, each with 2 stamens; stems scabridulous or smooth; [OK to TX, and westwards and southwards]

             7 Lower cymules with 2 staminate flowers, one with 3 stamens and one with 2 stamens; stems smooth; [se. GA south to s. FL]

1 Plant a floating aquatic; [subgenus Phyllanthus; section Loxopodium]

1 Plant a rooted terrestrial.

  2 Plants woody, shrubs or trees, 10-100 dm tall.

    3 Ultimate branchlets terete; leaves on ultimate branchlets well-developed, falling with the branchlet; fruits drupes; tree to 10 m tall

    3 Ultimate branchlets flattened into cladodes; leaves on ultimate branchlets scale-like, caducous; fruits capsules; shrub to 3 m tall; [subgenus Xylophylla; section Xylophylla]

  2 Plants perennial or annual herbs, or woody (suffrutescent) at the base only, 0.5-5 dm tall.

      4 Plant with “normal” arrangement of branches and leaves (leaves uniformly distributed on the stem and branches, alternate and either distichous or spirally arranged, the ultimate branches not deciduous, flowers produced on ultimate and penultimate orders of branches).

        5 Leaves arranged spirally; staminate sepals 0.7-2.5 mm long; stipules not auriculate; [section Paraphyllanthus].

        5 Leaves arranged distichously; staminate sepals 0.5-0.7 mm long; stipules typically auriculate; [subgenus Phyllanthus; section Loxopodium].

          6 Stems flattened and winged; filaments connate; seeds 1.3-1.5 mm long; [of e. LA westward]

          6 Stems terete; filaments free; seeds 0.7-1.1 mm long; [widespread in our region].

             7 Pistillate sepals 0.2-0.3 mm wide; leaf venation clearly visible on the lower surface; stems glabrous; cymules with 1 staminate and (1-) 2-3 (-5) pistillate flowers; pistillate nectary cupular, unlobed, enclosing the ovary 1/3-1/2 of its length; [widespread in our region]

             7 Pistillate sepals (0.2-) 0.3-0.5 (-0.7) mm wide; leaf venation obscure on the lower surface; stems scabridulous; cymules with 1-2 staminate and 1-2 pistillate flowers; pistillate nectary annular, unlobed or 6-lobed, enclosing the ovary only basally; [s. FL]

      4 Plant with “phyllanthoid” arrangement of branches, leaves, and flowers (leaves lacking on the main stem, the penultimate order of branches with scales arranged spirally, the ultimate order of branches deciduous, bearing normal leaves alternately and distichously, flowers produced only on the ultimate, deciduous branches), the ultimate branches and their distichous small leaves resembling the rachis and leaflets of a once-pinnate compound leaf.

               8 Stamens 3, filaments connate into a column 0.1-0.15 mm long; fruiting pedicels thicker and often also shorter, spreading in fruit; seeds variously ribbed or striate.

                 9 Fruiting pedicels 0.5 mm long; seeds with 12-15 transverse ridges and sometimes 1-3 pits; male flowers borne toward the tip of the branchlets, female flowers toward the base; [section Urinaria]

                 9 Fruiting pedicels > 0.5 mm long; seeds either longitudinally ribbed or striate, or verrucose; female flowers borne toward the tip of the branchlets, male flowers toward the base; [section Phyllanthus].

                   10 Pistillate sepals (0.5-) 0.7-1.5 mm long, 1-veined or obscurely veined; staminate sepals 0.3-1 mm long; seeds longitudinally ribbed, 0.8-1.5 mm long; capsules 1.7-2.7 mm in diameter; pistillate nectary of 3 glands or annular and 5-9-lobed

                   10 Pistillate sepals 3-3.5 mm long, pinnately veined; staminate sepals 1.5-3 mm long; seeds verrucose, 1.5-1.8 mm long; capsules 3.5 mm in diameter; pistillate nectary annular, unlobed; [subgenus Phyllanthus; section Phyllanthus]