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Key to Geranium

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1 Perennial, from a stout rhizome; [subgenus Geranium].
  2 Cymules 1-flowered (rarely a few cymules 2-flowered); pedicels with eglandular hairs only.
    3 Petals 15-22 mm long; fruit 28-42 mm long
    3 Petals 4-6 mm long; fruit 14-20 mm long
  2 Cymules 2-flowered; pedicels with a mixture of glandular and eglandular hairs (except with eglandular hairs only in G. maculatum).
      4 Pedicels with eglandular hairs only; petals 11-16 mm long; [native, common in much of our area (and also sometimes cultivated)]
      4 Pedicels with a mixture of glandular and eglandular hairs; petals either 6-9 or 12-29 mm long; [exotic, rare and in disturbed situations].
        5 Fruit 30-37 mm long; petals 12-24 mm long
        5 Fruit 14-27 mm long; petals either 6-9 mm long or 15-29 mm long.
          6 Petals 15-29 mm long; mericarp callus absent; fruits 15-27 mm long
          6 Petals 6-9 mm long; mericarp callus present; fruits 14-20 mm long
1 Annual, from a taproot.
             7 Leaves compound, at least the terminal segment (and often also the two lateral segments) petiolulate, not connected to the lateral segments by leaf tissue; petals 9-14 mm long; [rare in our area, mainly northward]; [subgenus Robertium, section Ruberta]
             7 Leaves dissected, but not compound, all segments interconnected by leaf tissue; petals 2-10 mm long; [collectively common and widespread in our area].
               8 Sepals blunt or acute, or terminating in a minute callus tip (mucro) < 0.3 mm long; [subgenus Robertium, section Batrachioidea].
                 9 Mericarps appressed pubescent across the surface, not ridged; stem pubescence of short (< 0.3 mm long), gland-tipped and eglandular hairs; stamens partly sterile (the inner 5 fertile, the outer 5 lacking anthers)
                 9 Mericarps glabrous across the surface (slightly to densely ciliate at the base), either reticulately ridged or not; stem pubescence an admixture of long eglandular hairs (1.0-1.7 mm long) and short (< 0.5 mm long) gland-tipped and eglandular hairs; stamens (all 10) fertile (note that anthers may fall readily).
                   10 Mericarps not reticulately ridged
                   10 Mericarps reticulately ridged
               8 Sepals awned or subulate, the subulate awn 0.7-3 mm long.
                     11 Mature pedicels < 1.5× as long as the calyx.
                       12 Mericarps with spreading hairs about 0.5 mm long, these often gland-tipped; [subgenus Geranium, section Dissecta]
                       12 Mericarps with long appressed hairs about 1 mm long, these not gland-tipped; [subgenus Geranium, section Geranium]
                     11 Mature pedicels > 2× as long as the calyx; [subgenus Geranium, section Geranium].
                          13 Pedicels glandular-villous
                          13 Pedicels retrorsely strigose