Willowherb Key

Ryedale Willowherb Key (Epilobium spp.)

by Gill Smith

I devised this key to kelp me sort out the various willowherb species growing in this area. I hope it will be the first of several keys to “difficult” groups, and although drawn up specifically for Ryedale plants I hope it might be useful for others. All are Epilobium species apart from Rosebay or fireweed. Please contact Gill with any comments.

1	Tall plant, asymmetrical flowers in a spike Flowers symmetrical, not in a spike	rosebay (Chamerion angustifolium) 2
2	Plant with obviously hairy stem and hairy leaves Plant with no or inconspicuous hairs and hairless leaves	3 4
3	Plant large (c. 4'), flowers >½" across, rose-purple with white centre, stigma with 4 lobes curved back Plant c. 2', flowers c. ¼", purple, stigma with 4 ± straight lobes	hirsutum parviflorum
4	Plant tiny, leaves ± round Stigma 4-lobed; very common Stigma undivided, club-shaped	brunnescens montanum 5
5	Plant greyish, leaves strap-shaped, untoothed, stem round, in ± acidic bogs Plant green or reddish, leaves usually toothed, stem mostly with 2 or 4 raised lines	palustre 6
6	Leaves with obvious longish (c. ½") stalks, flowers pale rose pink with white buds Leaves short-stalked, flowers pale mauve sometimes with darker tips, plant often reddish, petals deeply cleft (to c. ½-way), petals straight, opening wide giving cross-shaped flowers [glandular hairs on stem] Leaves almost or quite without stalks, running down onto the stem	roseum ciliatum 7
7	Leaves ±ovate, flowers deep rose, petals shallowly notched, seedpods relatively short and straight on long stalks c. ½", prefers damp places, flowers often not opening fully, plant often rather weak and floppy [stem hairs appressed, glandular hairs on calyx] Leaves ±strap-shaped, rather stiff and ±appressed to the stem, flowers lilac veined darker, not opening wide and flat, petals shallowly notched, seedpods relatively long and curved on short stalks c. ¼", plant stiff and “upright” [all hairs on stem and calyx appressed]	obscurum tetragonum

Notes: The hairs on the stems and calyx of Epilobium ciliatum, obscurum and tetragonum can only be seen with a lens. Note also that colour is not a good determinant especially between obscurum and tetragonum. This key does not include species that do not grow in Ryedale.

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