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Key to Lythraceae

Lythraceae

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1 Plant woody or suffrutescent, a shrub or a small tree 1-10 m tall; petal present, showy, 8-20 mm long.
  2 Aquatic shrubs with arching suffrutescent or woody stems; leaves opposite or whorled; [native]
  2 Terrestrial shrubs or small trees with erect woody stems; leaves alternate to subopposite; [exotic cultivated and sometimes persistent].
    3 Stems unarmed; flowers in many-flowered terminal or axillary cymose panicle; fruit a loculicidal capsule, the seeds unilaterally winged (wings growing from one side)
    3 Stems often armed with thorn; flowers solitary or several in terminal or axillary clusters; fruit a leathery berry (pomegranate), the seeds with a fleshy outer layer and hardened inner layer, but not unilaterally winged
1 Plant not woody, an herb 0.1-1.2 m tall; petal absent or present, inconspicuous or showy, 1-10 mm long.
      4 Fruit with 2-4 prominent spine; leaves coarsely toothed
      4 Fruit not spinose; leaves entire.
        5 Stems pubescent.
          6 Floral tube (hypanthium) swollen obliquely at its base; capsule dehiscing longitudinally along the upper surface
          6 Floral tube (hypanthium) symmetrical; capsule dehiscing septicidally at the apex
        5 Stems glabrous.
             7 Floral tube cylindric to turbinate, about 2× as long as wide
             7 Floral tube campanulate to globose, about 1× long as wide.
               8 Flowers or fruits (1-) 3-10 in the leaf axil (at least some axil with 2 or more flowers or fruits on a given plant)
               8 Flowers or fruits solitary in the leaf axil (never > 1 per axil).
                 9 Capsule indehiscent; petal 0; sepal 4, broadly triangular, lacking intersepalary appendage; seeds spatulate or oblanceolate, about 1 mm long, minutely granular on one face and smooth on the other
                 9 Capsule dehiscing septicidally; petal 0 or 4; sepal 4 (-6), triangular, with intersepalary appendage of size about equal to the calyx lobe; seeds hemispheric, about 0.3 mm long, the surface very finely reticulate

Key C5: rooted aquatics with cauline leaves, compound or divided

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1 Leaves (or leaf-like adventitious root) 1-pinnately compound or divided (with a central axis bearing pinnae, the pinnae not further divided).
  2 Leaves crowded at the upper end of the stem, supported by inflated branches
  2 Leaves (or leaf-like adventitious root) spaced along the stem, no branches inflated.
    3 Emersed leaves diamond-shaped, the blade < 2× as long wide, serrate only in the upper portion of its length
    3 Emersed leaves lanceolate, the blade > 4× as long as wide, serrate along its length
1 Leaves dichotomously or otherwise complexly (2-3×) compound or divided.
      4 Plants bearing numerous bladder-like traps
      4 Plants lacking bladder-like traps.
        5 Leaves alternate; leaf segment complexly (but not dichotomously) branched.
          6 Leaf dissection 2-pinnate to 3-pinnate; flowers in raceme; petal 4, white
          6 Leaf dissection 2-ternate to 3-ternate; flowers solitary; petal 5, yellow or white
        5 Leaves opposite or whorled; leaf segment dichotomously branched.
             7 Leaves whorled; leaf segment entire or toothed with denticle.
               8 Leaf segment toothed with denticle
               8 Leaf segment entire
             7 Leaves opposite; leaf segment entire.
                 9 Leaves sessile
                 9 Leaves petiolate

Key C6: rooted aquatics with simple, cauline, alternate leaves

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1 Leaves broad, < 4× as long as wide.
  2 Floating leaves peltate
  2 Floating or emersed leaves cuneate to rounded at base.
    3 Floating leaves diamond-shaped, prominently serrate
    3 Floating or emersed leaves elliptic or suborbicular.
      4 Leaves emersed, lanceolate to narrowly elliptic; flowers 5-merous; [Eudicot]
      4 Leaves emersed or floating, suborbicular or elliptic (if emersed, then suborbicular; flowers 3-merous; [Monocot].
        5 Leaves emersed, suborbicular
        5 Leaves floating, elliptic
1 Leaves narrow, > 4× as long as wide.
          6 Leaves 0.3-1.4 cm long, very numerous and tightly spaced
          6 Leaves 2-35 cm long, fewer and scattered along the stem.
             7 Leaf divided into a sheath and blade, with a ligule 0.5-8 mm long at the juncture; inflorescence a spike, raceme, or panicle of spikelet
             7 Leaf not divided into a sheath and blade, but if basally sheathing lacking a ligule (though sometimes with 1-2 conspicuous stipule); inflorescence various, but not as above.
               8 Leaves terete, to 35 cm long, 0.3-2 mm wide; plants of marine habitats, growing submersed in salt water; [FL and the Gulf Coast of AL, MS, and LA]
               8 Leaves flat or terete, to 200 cm long; plants of fresh or brackish waters (if of marine waters, Zostera, the leaves obviously flat, 1.5-6 mm wide); [collectively widespread].
                 9 Leaves filiform, terete or nearly so; stipule present, adnate to the leaf base and forming a sheath around the stem > 10 mm long.
                   10 Stipule free at its tip, the sheathing portion not appearing inflated; flowers > 2, in an interrupted spike
                   10 Stipule adnate its entire length to the leaf base, appearing inflated; flowers usually 2, on a flexous, elongate peduncle
                 9 Leaves flat; stipule absent, or if present, either free or adnate to the leaf base and forming a sheath for < 10 mm.
                     11 Leaves lacking a midvein; perianth parts 6, yellow
                     11 Leaves with a midvein; perianth parts 0 or 4, variously colored (not yellow).
                       12 Plants pubescent (at least on the upper stem); leaves pinnately veined; [Eudicot]
                       12 Plants nearly or entirely glabrous; leaves with parallel venation; [Monocot].
                          13 Inflorescence of flowers solitary or in 2-4 flowered raceme, axillary; spathe lacking; perianth conspicuous with 3 pink to purple petal
                          13 Inflorescence a spike, terminal or axillary; with or without a spathe; perianth lacking.
                            14 Inflorescence a cylindrical, interrupted spike, lacking a spathe; leaves either parallel-margined or variously with a narrow blade differentiated from a petiole; [fresh to brackish waters]
                            14 Inflorescence either a flattened spike sheathed by a spathe-like bract, or solitary; leaves parallel-margined, to 20 dm long; [saline (marine) to brackish waters].
                              15 Leaves with a notched or tricuspidate apex; flowers solitary; [e. NC southward]
                              15 Leaves with a rounded apex; flowers in a flattened spike sheathed by a spathe-like bract; [e. NC northward]