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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
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Key to Galium, Key A: Bedstraws with leaves mostly 6 per node (ranging from 4-8)

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1 Flowers pink, purple, or blue, in terminal heads, subtended by an involucre of leaves fused at the base; stem rough-hairy or retrorse-scabrid; [exotic].
  2 Leaves obtuse at tip; leaves 6-8 per whorl; stem retrorse-scabrid
  2 Leaves acute to acuminate at tip; leaves (4-) 6 per whorl; stem rough-hairy
1 Flowers white, yellow, or green, in axillary or terminal diffuse inflorescences, not subtended by an involucre; stems either smooth, retrorse-scabrid, or pubescent.
    3 Largest leaves < 10 mm long; fruits 0.7-1 mm across; annual; [exotic].
      4 Inflorescence relatively diffuse, branches divaricate; ultimate fruits (2-) 3-6 (-7) nodes beyond primary stem axis (with largest leaves); first inflorescence internode (beyond primary stem axis) 15-50 mm long; fruit surface glabrous (without hairs)
      4 Inflorescence relatively strict, branches ascending; ultimate fruits 2-3 (-4) nodes beyond primary stem axis (with largest leaves); first inflorescence internode (beyond primary stem axis) 3-12 (-20) mm long; fruit surface glabrous or bristly-hispid.
        5 Fruit surface without hairs, smooth to shallowly papillate
        5 Fruit surface bristly-hispid with uncinate-tipped hairs, distinctly papillate
    3 Largest leaves > 10 mm long; fruits 1-2.5 mm across; perennial; [native].
          6 Fruits and ovaries uncinate-hispid; leaves 15-50 mm long, 7-10 mm wide
          6 Fruits and ovaries glabrous or papillose; leaves 5-25 mm long, 1-6 mm wide.
             7 Corolla 1.5-2.5 mm across, 3-lobed; [collectively widespread in our region].
               8 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
               8 Fruiting pedicels (2-) 2.5-5 (-6) mm long; pairs of fruits (2-) 2.5-3 mm across at maturity; leaves (1.5-) 2-2.5 (-2.8) mm wide
             7 Corolla 2.5-4.5 mm across, 4-lobed; [mostly of the Mountains in our area, extending into the Piedmont or even the Coastal Plain in n. VA and northward].
                 9 Leaf margins retrorsely ciliate-scabrid; leaves 3-5× as long as wide; [plants of bogs and moist thickets]
                 9 Leaf margins antrorsely ciliate-scabrid; leaves 4-8× as long as wide; [plants of dry forests and woodlands].