Epilobium

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  1a. Stigma 4-lobed; plants evidently long-villous; petals 10–16 mm long (only 4–9 mm in the very rare E. parviflorum)
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    E. hirsutum

    2a. Petals 10–16 mm long, with a shallow notch; leaves sessile and somewhat clasping 
the stem
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    E. parviflorum

    2b. Petals 4–9 mm long, with a deep notch; leaves sessile or subsessile, but not clasping the stem
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  1b. Stigma entire or nearly so; plants ± glabrous to short-pubescent; petals 2–10 mm long
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    3a. Leaf blades with entire or undulate, usually revolute, margins [Fig. 741]; pubescence of the stem not in decurrent lines from the leaf bases; plants perennating from turions at the tips of stolons
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      E. strictum

      4a. Plants pubescent with divergent hairs (note: this best viewed along the main axis 
of the stem) [Fig. 741]
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      4b. Plants pubescent with appressed hairs
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        E. palustre

        5a. Leaf blades essentially glabrous on the adaxial surface, 2–15 mm wide; inflorescence nodding in bud
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        E. leptophyllum

        5b. Leaf blades strigose-puberulent on the adaxial surface, 1–7 mm wide; inflorescence erect to arching in bud
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    3b. Leaf blades with usually toothed, flat margins (entire in E. anagallidifolium); pubescence of the stem in decurrent lines from the leaf bases; plants perennating from sobols, rosettes, or sessile turions
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      6a. Stems matted, decumbent to erect, soboliferous, usually unbranched above the base of the plant, 0.5–4.5 dm tall; plants boreal and alpine
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        E. anagallidifolium

        7a. Leaf blades 10–25 ×3–7 mm, ± entire (rarely very weakly toothed); outer surface of seed smooth; capsules mostly 23–40 mm long; stems mostly 2–10 cm tall; petals pale purple in life, 3–4.5 mm long
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        7b. Leaf blades 19–40 × (6–) 8–15 mm, weakly serrate; outer surface of seed minutely papillose or minutely pitted; capsules mostly 35–75 mm long; stems 6–40 cm tall; petals white to pale purple, 2.5–8 mm long
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          E. lactiflorum

          8a. Petals white, 2.5–4 mm long; outer surface of seed minutely pitted; inflorescence erect prior to anthesis; sobols epigeal (though often short and inconspicuous)
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          E. hornemannii

          8b. Petals pale purple in life (rarely white; often fading to white with pink, red, or blue tinging in drying), 4–8 mm long; outer surface of seed minutely papillose; inflorescence nodding prior to anthesis; sobols hypogeal
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      6b. Stems usually solitary, erect, without sobols, usually branched above the base of the plant, (0.5–) 3–10 dm tall; plants of various habitats, commonly found at lower elevations
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        E. coloratum

        9a. Coma brown; flower buds pointed at the apex due to the projecting sepal tips; seeds minutely papillose, without a beak; leaf blades gray-green, rugose-veiny
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        E. ciliatum

        9b. Coma white or nearly so; flower buds obtuse to rounded at the apex; seeds longitudinally striate, with a broad, short beak; leaf blades without gray color, not or only slightly rugose-veiny

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