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Key to Hydrogalium

Rubiaceae

Hydrogalium

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1 Stems smooth on the angles or with few, scattered hairs; stem nodes densely retrorsely bearded; corollas 4-lobed, the lobes longer than wide; leaves strictly 4 per node (very rarely 5 at a few nodes).
  2 Leaves strongly down-curved when fully grown; leaves 1-2.5 mm wide
  2 Leaves spreading; leaves (0.5-) 0.8-5 (-6) mm wide
    3 Leaves (8-) 10-20 (-25) mm long, (0.5-) 0.8-2 mm wide, margin usually smooth, with strongly down-rolled margins; corolla (1.8-) 2-2.5 (-3) mm across; pedicels filiform; stems 15-50 (-60) cm long, delicate
    3 Leaves (10-) 15-25 (-30) mm long, (2-) 3-5 (-6) mm wide, margin scabrous, not down-rolled; corolla (2-) 2.5-3.5 (-4) mm across; pedicels thicker; stems (15-) 25-60 (-80) cm long, firm
1 Stems retrorsely scabrous on the angles; stem nodes not conspicuously bearded; corollas 3-4-lobed, the lobes about as wide as long, or wider than long; leaves 4 per node, but most plants with at least some main stem nodes with 5 or 6 leaves.
      4 Inflorescences of 3-4 flowers, not repeatedly forked; corolla lobes 3 (-4).
        5 Flowers and fruits borne on arcuate pedicels, (5-) 7-15 (-20) mm long and densely retrorsely scabrous
        5 Flowers and fruits borne on straight pedicels, these (2-) 2.5-8 (-12) mm long and smooth.
          6 Fruiting pedicels (4-) 5-8 (-12) mm long; pairs of fruits (3-) 3.5-5 mm across at maturity; leaves 2-3 (-4) mm wide
          6 Fruiting pedicels (2-) 2.5-5 (-6) mm long; pairs of fruits 2-3 mm across at maturity; leaves (1.5-) 2-2.5 (-2.8) mm wide