DHBlog029 · Hedera helix vs. Hedera hibernica by Robert Sharp
There once was a time when seeing an Ivy, provided it wasn’t splashed with cream or white, must have elicited a slightly warm feeling in a botanist, confident in the knowledge that this was Hedera helix. Alas, those times are long gone. Back in 1990, McAllister and Rutherford published a paper that explained where we thought there was just one species, there had actually been two. Not cryptically hidden in the DNA, but characterised by a range of differences: the stellate hairs or trichomes, shape of the leaf, colouration, even its smell. This new species was Hedera hibernica or Atlantic Ivy and, unsurprisingly given the name, was confined to the Atlantic west of the country. (Not new to science perhaps.)
It took some time for the new species to catch on. In Dorset, to begin with, H. hibernica was discerned to be growing at least in the Purbeck Hills. Then it seemed to be more widespread and some botanists even put forward the radical claim that all Ivy in Dorset was H. hibernica. The problem is that telling the two apart, in the field at least, is not easy and older leaves lose their tell-tale hairs except those most adpressed to the surface, giving them the appearance of being H. hibernica. Confusion reigned so much that a third species appeared: Hedera helix/hibernica. This is not a hybrid but a social construct to paper over the problems in resolving plants into one taxon or the other.
The confusion continues despite the BSBI publishing an article aimed to resolve it. Unfortunately, Alison Rutherford leaves the reader believing that identification requires the growth of a cutting of the plant. A useful technique but not practical in the field.
I spend a fair amount of time in the North of the county and I was sure that most of the plants up there (where the wind blows strange tunes through the long-forgotten hills) were H. helix. I have been informally collecting and studying young shoots for several years now and so I decided to try to pin the problem down sufficiently that field identification can be done, albeit not for every plant you find.
Now (April) is a good time to start looking, so this is my approach:
find a shoot growing up or down a substrate: tree or wall, that has new shoots growing from the old leaf axils, with fresh young leaves; check that the new stems and leaves are covered in hairs.
using a 10x or better hand lens and holding the new leaves and stems up to the light take a close look at the hairs. Don’t look at individual hairs so much as the general appearance. Both species can have adpressed and omni-directional hairs and the latter are quick to be shed, which is why it is best to look only at young leaves, or better still, a young petiole. H. hibernica has a neat, well-groomed appearance while H. helix looks like it would benefit from a haircut.
note the shape of the new leaves growing on your shoot. Is the central lobe much longer than wide or about the same?
check the colour of the new leaves. There may be some red wine splashes that differ from small speckling to a very obvious dunked look;
take one of the fresh shoots and roll and crush it between you finger and thumb. Check if the smell is distinctly acrid or not. Don’t bother with sweetness or the like, I have never noticed it and don’t try with older leaves.
| H. helix | H. hibernica |
Hairs | stellate, omni-directional, messy | stellate, adpressed, neat |
Leaf Lobe Shape | Elongated, >2x width | Stubby, < 2x width |
Colour | Often suffused with wine red | Sometimes speckled with wine red |
Smell | Acrid | Not acrid |
I have ignored several of the characteristics referred to by McAllister and Rutherford because they are more difficult to assess in the field, often more variable and likely to make the whole task too onerous.
Some tips to achieving success:
Ignore geography! I know of no reason the two taxa cannot be found together. Just because you are in the Purbeck Hills doesn’t mean you can not find H. helix.
Ignore most of the plant, especially fertile parts with large leaves on long petioles. It can take time to find an appropriate shoot. There may not be any within reach. Do not try with any other part of the plant. Accept no substitutes! That is why Alison Rutherford recommends taking cuttings!
Store your specimens in something that will protect the hairs – an empty lunch box is a good example and some think a reason to eat earlier in the day! Do not stuff your specimens into plastic bags.
Do not take much notice of the hairs growing on the leaf margins – flat hairs can stick out and look a lot like omni-directional hairs. Do not bother cutting sections because you will probably flatten the hairs in the process (I tried). Be careful after heavy rain, which dislodges the hairs and again can make them stick up more. Finally, avoid windswept plants.
If all the characters line up then accept the ID, otherwise forget it. An exception could be smell, especially if your memory for smells is not so good. Do not waste time on indeterminate specimens but if you want to record it, use the H. helix/hibernica taxon on Living Record.
Try to find both species so you can compare them in all these characteristics. The more often you examine both the easier it is to tell them apart.
I am not an expert but I am sure this is something that can be determined in the field provided you have an open mind and are prepared to keep trying. If you are struggling to get comfortable with deciding which one you keep finding, then next time you travel eastwards, if your default is H. hibernica, or westwards if H. helix, take a moment to collect some ivy and take it home.
References
McAllister, H.A. & Rutherford, A. (1990) Hedera helix L. and H. hibernica (Kirchner) Bean (Araliaceae) in the British Isles. Watsonia 18, 7-15
Rutherford, A. (2023) “Ivy Confusions?”, BSBI News 152, 28-30
Further Reading
Stace, C.A. (2019) New Flora of the British Isles. C&M Floristics, Suffolk, pp. 838-840
Rutherford, A. (1998) “Hedera”. In: Rich, T.C.G and Jermy, A.C. (eds.) Plant Crib. BSBI, pp.216-219
Acknowledgements
Robin Walls and I have discussed the Ivy Problem for several years and Robin was kind enough to proof-read the article and provide suggestions.