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Galium
See list of 22 species in this genusCorolla measurements provided in the key were based on dried specimens. References: Ehrendorfer (1976), Puff (1976).
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2a. Principal leaves with 3 or 5 nerves [Fig. 875]; schizocarps bristly (sometimes glabrous in G. boreale) [Fig. 876]
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3a. Corolla white to cream-white; leaf blades broad-linear, 1–2.5 mm wide; bristles of the schizocarp, when present, not hooked at the apex; angles of the stem commonly retrorse-scabrous
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3b. Corolla green-purple, purple, or yellow-green; leaf blades ovate to obovate or elliptic to oval, 5–25 mm wide; bristles of the schizocarp hooked at the apex [Fig. 876]; angles of the stem glabrous or pubescent, but not retrorse-scabrous
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4a. Flowers all pedicellate at the tips of the inflorescence branches; leaf blades 10–30 mm long
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5a. Flowering stems with 2–4 (–5) nodes; distal leaf blades larger than proximal leaf blades; corolla yellow-white
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5b. Flower stems with more than 6 nodes; leaf blades of ± uniform size along the stem; corolla green-white to purple
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4b. Some of the flowers sessile along the branches of the inflorescence [Fig. 875]; leaf blades 20–80 mm long
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6b. Leaf blades elliptic to lanceolate, widest usually below the middle, acute to acuminate at the apex; petals glabrous, acuminate at the apex
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7a. Cymes branched 3 or more times, bearing 5 or more flowers [Fig. 879]; some of the pedicels spreading, especially in fruit (in part)
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7b. Cymes branched 1 or 2 times, bearing 2–4 flowers [Figs. 880,881]; pedicels mostly erect to ascending (often divaricately spreading in G. tinctorium)
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8a. Corollas mostly 3-merous, 0.8–2.5 mm in diameter, the obtuse lobes as wide as or wider than long; stems often retrorse-scabrous on the angles [Fig. 881], usually not densely short-bearded just below the nodes; plants developing prostrate, basal offshoots late in the season
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9a. Fruiting pedicels ± straight, stiff, lacking scabrules, usually some divaricately spreading (sometimes somewhat arcuate and/or with a few scabrules in G. tinctorium ssp. floridanum) [Fig. 880]; corolla 1.5–2.5 mm in diameter
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9b. Fruiting pedicels arcuate, scabrous or, less commonly, smooth, mostly erect to ascending [Fig. 881]; corolla 0.8–1.5 (–1.6) mm in diameter
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10a. Corolla 0.8–1 mm in diameter; leaf blades 5–8 (–12) × (0.8–) 1–2 (–3) mm; mature schizocarps 1.8–2 (–2.3) mm wide; fruiting peduncles 1.5–5 mm long, smooth
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10b. Corolla 1.2–1.5 (–1.6) mm in diameter; leaf blades (7–) 8–20 (–25) × (1–) 1.2–5 (–6) mm; mature schizocarps (2–) 2.2–3.5 (–4) mm wide; fruiting peduncles (2–) 3–15 (–20) mm long, scabrous or smooth
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8b. Corollas 4-merous, 2–3.5 mm in diameter, the acute lobes longer than wide; stems not scabrous on the angles [Fig. 878], densely short-bearded just below the nodes [Fig. 878]; plants not developing basal offshoots in late season
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11a. Leaf blades 10–30 ×1–6 mm, ascending to spreading; mericarps 4–5 mm in diameter, tuberculate, usually only 1 developing; stems 2–8 dm tall
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11b. Leaf blades 8–15 ×1–3 mm, spreading to deflexed; mericarps 2–3 mm in diameter, smooth, usually both developing; stems 1–4 dm tall
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1b. Primary axis and main branches with 5–12 leaves at each node [Fig. 877]
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13a. Cymes branched 3 or more times, bearing 5 or more flowers; some of the pedicels spreading, especially in fruit; corollas 4-merous, 2.5–3.3 mm wide, the lobes longer than wide (in part)
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13b. Cymes branched 1 or 2 times, bearing 2–4 flowers; pedicels mostly erect or ascending; corollas mostly 3-merous, 0.8–2.5 mm wide, the lobes as wide as or wider than long
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12b. Leaf blades sharply pointed to cuspidate at the apex
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14a. Corolla 0.5–1 mm in diameter, yellow-red; schizocarps 1–1.4 mm wide, finely papillose on the surface
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14b. Corolla 1–7 mm in diameter, white, green-white, or yellow; schizocarps 2–6 mm wide, smooth or uncinate-bristly (papillose with pointed projections in G. tricornutum, but then the schizocarps 3–5 mm wide)
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15a. Pedicels strongly recurved to deflexed post anthesis; schizocarps papillose with pointed projections
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15b. Pedicels erect to spreading; schizocarps smooth or uncinate-bristly
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16a. Stems scabrous on the angles of the internodes (at least on the proximal internodes), reclining to upright; inflorescences relatively few-flowered, each with 2–5 flowers, usually once- or twice-branched (note: a given plant can bear multiple such inflorescences)
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17a. Leaves (6–) 8 per node; plants annual, with a short taproot; mericarps 2–4 (–5) mm in diameter
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17b. Leaves (4–) 6 per node; plants perennial, with creeping rhizomes; mericarps 1.5–2 mm in diameter
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18a. Schizocarps glabrous; leaf blades 8–20 ×2–6 mm, retrorsely scabrous on the margin; corolla white
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18b. Schizocarps uncinate-bristly [Fig. 876]; leaf blades 15–85 ×4–13 mm, antrorsely scabrous on the margin; corolla green-white
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16b. Stems glabrous or pubescent on the internodes, but without scabrules, usually upright; inflorescences relatively many-flowered, each with 5–20 or more flowers, usually 2 or more times branched, collectively forming a large, open, cymose panicle [Fig. 877]
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19a. Corolla funnelform, 4–7 mm in diameter; schizocarps covered with uncinate bristles; stems retrorsely hispid at the nodes
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19b. Corolla rotate, 2–3 (–5) mm in diameter; schizocarps smooth; stems glabrous or pubescent, but without a distinct ring of hairs at the nodes
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20a. Leaf blades narrow-linear, 0.5–2 (–3) mm wide, the margins prominently revolute (sometimes the margins even recurved as far as the midrib), (6–) 8–12 per node; lobes of corolla merley acute at apex (rarely with an obscure apiculus in G. verum)
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21a. Corollas yellow, rotate, 2–3.5 mm in diameter; schizocarps 1–1.5 mm wide
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21b. Corollas white, cupuliform, 4–6 mm in diameter; schizocarps 1.5–2 mm wide
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20b. Leaf blades linear to elliptic, (1–) 2–10 mm wide, not or only slightly revolute, 6–8 per node; lobes of corolla apiculate at apex or usually merely acute in G. sylvaticum
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22a. Leaf blades 20–40 mm long, glaucous abaxially, distinctly paler than the adaxial surface; pedicels capillary, mostly 0.05–0.1 mm thick
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22b. Leaf blades 10–25 (–40) mm long, not glaucous abaxially, only somewhat paler than the adaxial surface; pedicels relatively thicker, mostly 0.08–0.2 mm thick
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23a. Corolla 2–3 (–3.3) mm in diameter; pedicels usually longer than the diameter of the flower; inflorescence lax and open, the branches divaricately spreading post anthesis
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23b. Corolla (2.5–) 3–5 mm in diameter; pedicels usually shorter than the diameter of the flower; inflorescence relatively dense, the branches ascending to spreading post anthesis
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Each photo represents one species in this genus.