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Key to Hedera

Araliaceae

Hedera

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1
Trichomes scale-like, 0.1-0.4 mm, reddish brown or white in color, those on the leaves, petioles, and young stems with rays fused basally for 1/4 to 1/2 their length; juvenile leaves lobed (at least slightly, as in H. algeriensis) or unlobed (H. colchica).
  2
Juvenile leaves lobed, fresh leaves not strong-scented when crushed; center of trichomes < 0.05 mm across
 ⇒ Hedera algeriensis
  2
Juvenile leaves orbicular and coriaceous, little or not at all lobed, strong-scented when crushed; center of trichomes > 0.05 mm across
 ⇒ Hedera colchica
1
Trichomes stellate, 0.5-1.0 mm, white in color, those on the leaves, petioles, and young stems with rays fused basally for < 1/8 their length; juvenile leaves slightly to deeply lobed.

(c) Thomas - CC-BY
  3
Hairs of young stems, leaves, and petioles whitish, the rays erect (at a right angle to the leaf surface); juvenile leaves usually < 8 cm wide, usually dark green and often also marbled with white, often lobed > ½ the way to the base; [often strongly climbing]
 ⇒ Hedera helix
  3
Hairs of young stems, leaves, and petioles yellowish-brown to rusty-brown, the rays not erect (parallel to the leaf surface); juvenile leaves often > 8 cm wide, usually medium green (rarely also marbled with white), usually lobed < ½ the way to the base; [usually not climbing]
 ⇒ Hedera hibernica

(c) Thomas - CC-BY