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Support the Flora of the Southeastern US

2024 has been a banner year for making the best flora we can imagine. We've created:
With financial support from people like you, we are aiming even higher in 2025. Together we can accomplish all this: Vote on our 2025 priorities
  • Add Global Conservation Ranks (GRanks) vote
  • Professional graphic keys (polyclaves) to individual families/genera vote
  • 2 new FloraQuest apps: Florida & Mid-South vote
  • Image overlays highlighting diagnostic characters with arrows vote
  • iNaturalist integration in FloraQuest vote
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Click the number at the start of a key lead to highlight both that lead and its corresponding lead. Click again to show only the two highlighted leads. Click a third time to return to the full key with the selected leads still highlighted.

Key to Sparganium

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1 Stigmas 2-branched; fruits truncate at apex, obpyramidal, very abruptly beaked, 4-8 (-10) mm broad; [subgenus Sparganium]
1 Stigmas 1-branched; fruits rounded or acuminate to a beak at the apex, elliptic, fusiform, or obovate, 1-4 mm broad; [subgenus Xanthosparganium].
  2 Leaves and inflorescence primarily emergent, with few or no leaves floating on water surfaces; leaves keeled throughout or at least basally.
    3 Rachis of inflorescence unbranched; fruit beak straight to curved; tepals reaching about half the length of fruit body; leaves often keeled distally; perianth segments essentially translucent and lacking an apical dark spot
    3 Rachis of inflorescence branched; fruit beak curved; tepals reaching about half or more the length of fruit body; leaves usually keeled only near bases (S. americanum) or from base to at least the middle of leaves (S. androcladum(); perianth segments not translucent, their apices with a dark brown or black pad of tissue.
      4 Mature fruits dull, finely pitted, the body 3-5 mm long; fruiting heads 1.5-2.5 cm in diameter; branches of the inflorescence with (0-) 1-3 pistillate heads (in addition to staminate heads); stigma 0.8-1.9 (-2.8 in the Coastal Plain) mm long; leaves erect but not stiffened
      4 Mature fruits shiny, smooth, the body 5.5-7 mm long; fruiting heads 2.5-3.5 cm in diameter; branches of the inflorescence with 0 (-1) pistillate heads (in addition to staminate heads); stigma 1.5-3 mm long; leaves stiff
  2 Leaves and inflorescence primarily floating, limp on the surface of water (sometimes with a few emergent stems); floating leaves usually without keels and mostly flattened or usually at least basally keeled (as in S. acaule).
        5 Rachis of inflorescence branched, the distal portion erect at water surface
        5 Rachis of inflorescence unbranched, either floating, the distal portion erect at water surface, or completely erect on entirely emergent plants.
          6 Staminate heads 1; pistillate heads borne directly in axils of leaves or bracts; beak of fruit 0.5-1.5 mm long
          6 Staminate heads 2 or more; pistillate heads (some or all) borne above the axils of leaves or bracts; beak of fruit 1.5-4.3 mm long
             7 Fruit beak straight to curved, 2-4.5 mm long, fruits green to reddish brown when fresh; floating leaves keeled at least basally; plants often a mix of (mostly) emergent and (some) floating leaves and inflorescences
             7 Fruit beak straight, 1.5-2. mm long, fruits reddish to brownish colored when fresh; floating leaves not keeled; plants floating