Epilobium Genus


        The Willow-herbs have recently become of more interest to me as I discovered that the plant that I have been calling Downy Willow-herb was not identified correctly. Following is information which I have found so far:

Willow-herbs listed in the Royal Botanical Garden checklist (R) and Hamilton-Wentworth Natural Areas Inventory (H)

Epilobium cilatum ssp. cilatum......Ciliate Willow-herb  (R) (H)
Epilobium cilatum ssp. glandulosum..Northern Willow-herb  (R) (H)
Epilobium coloratum.................Purple-veined Willow-herb  (R) (H)
Epilobium hirsutum..................Great Hairy Willow-herb (R) (H)
Epilobium leptophyllum..............Narrow-leaved Willow-herb (R) (H)
Epilobium parviflorum...............Sparse-flowered Willow-herb (R) (H)
Epilobium strictum..................Downy Willow-herb  (H)
[Downy Willow-herb is listed as "rare" and found at three locations in Hamilton/Wentworth.]

Following is a key to help sort out these wild flowers.
It is based on Edward Voss's Michigan Flora key but with technical
terms translated into standard English when possible.

1. Stems have horizontal, spreading, uncurved hairs
   2. Stigma (end of pistil) is a smooth curve; leaves less than 8 mm wide;
      leaves with smooth edges slightly rolled under
      = Epilobium strictum...Downy Willow-herb
   2. Stigma (end of pistil) is deeply 4-lobed; some leaves more than 8 mm wide;
      leaves with at least some teeth
      3. Leaves not clasping and with little or no stem; petals 10 mm or less
         = Epilobium parviflorum...Sparce-flowered Willow-herb
      3. Most leaves clasping with no stem; petals 11 to 17 mm long
         = Epilobium hirsutum...Great Hairy Willow-herb
1. Stems have no hairs or small incurved hairs
   4. Leaves long & narrow possibly wider below the middle of the leav; usually less
      than 4 mm wide but can be up to 1 cm wide; smooth edges; small incurved hairs 
      on top surface
      = Epilobium leptophyllum...Narrow-leaved Willow-herb
   4. Leaves may be wider below or at the middle of the leaf; often up to 1.5 cm wide;
      large toothed or with very small teeth
      5. Very small teeth on leaf margins; leaf stems with broad wings; 
         hairs of seeds whitish
         = Epilobium ciliatum...Ciliate Willow-herb
      5. Definite teeth on leaves; narrow or no wings on leaf stems; 
         hairs on seeds copper-coloured or brownish at maturity
         = Epilobium coloratum...Purple-veined Willow-herb

Dean A. Gugler
Amateur Naturalist
Retired Elementary School Teacher

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