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Key to Mimosa

Fabaceae

Mimosa

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1 Shrubs.
  2 Leaflets 15-43 per pinna.
    3 Pinnae 4-7 pairs per leaf; fruits breaking into 10-15 segments; [ s. TX southwards]
    3 Pinnae 5-16 (-22) pairs per leaf; fruits breaking into 14-21 segments; [naturalized, in our region known from FL]
  2 Leaflets (3-) 4-12 per pinna.
      4 Pinnae 1-8 pairs per leaf; leaflets 5-12 per pinna; fruits slightly to somewhat constricted between segments, but not jointed into segments
      4 Pinnae 1-3 (-4) pairs per leaf; leaflets (3-) 4-7 per pinna; fruits strongly constricted between seeds, jointed and breaking into segments
1 Herbs, sometimes suffrutescent, trailing, sprawling, or climbing (by means of recurved, catclaw prickles).
        5 Plant unarmed (rarely with widely scattered prickles), the stem with strigose hairs with bulbous bases, 0.5-3 mm long; capitula 1.5-3× as long as the diameter, 9-25 mm long
        5 Plant well-armed with recurved, catclaw prickles; capitula spherical or nearly so, 1-1.2× as long as wide, 3.5-14 mm long.
          6 Pinnae (1) 2-5 pairs per leaf; leaflets either 10-25 per pinna or 4-6 per pinna; fruits not quadrangular, the valves breaking into segments.
             7 Pinnae (1-) 2 pairs per leaf; leaflets 4-6 per pinna; [native, s. & se. TX southwestwards]
             7 Pinnae 3-5 pairs per leaf; leaflets 10-25 per pinna; non-native, waif]
          6 Pinnae 3-8 (-11) pairs per leaf; leaflets 5-25 per pinna; fruits normally quadrangular (sometimes compressed in M. roemeriana) because of widening of the replum, the valves remaining intact and not separating.
               8 Leaflets (9-) 10-17 (-19) pairs per pinna.
                 9 Venation of the lower leaf surface readily visible, pale; The midrib giving rise on both sides to 1 or more secondary veins.
                   10 Leaflets obtuse or with an obscure mucro; heads (not including the filaments) < 7 mm in diameter; [s. GA south to s. FL]
                   10 Leaflets sharply apiculate; heads (not including the filaments) 7-11 mm in diameter; [west of the Mississippi River, very rarely adventive eastwards].
                     11 Pod 20-45 mm long, densely armed on all ribs with spines that are basally confluent; valves of the pod as wide as or wider than the replum; [Coastal Plain, w. LA west to se. TX]
                     11 Pod 55-120 mm long, the spines separate from one another; valves of the pod narrower than the replum; [widespread west of the Mississippi River, Coastal Plain and inland (northwards)]
                 9 Venation of the lower leaf surface not visible (sometimes the upper surface with darkened and impressed veins).
                       12 Valves of the pod 3-6 mm wide, distinctly wider than the replum; [on limestone, caliche, and other calcareous substrates; sc. OK south through nc. TX to the Edwards Plateau, extending slightly into se. TX Coastal Plain]
                       12 Valves of the pod as wide as or narrower than the replum; [collectively widespread, usually not on calcareous substrates, at least not in TX]
                          13 Pinnae 4-8 pairs per leaf; seeds 3.2-5.2 mm long; [east of the Mississippi River, VA and KY south to s. FL and e. LA]
                          13 Pinnae 1-3 pairs per leaf; seeds (5-) 6-9 mm long; [west of the Mississippi River, sw. LA and TX southwestwards to COA]