Hello,
I’m looking for an identification key of Juncus effusus, which comprises the subspecies listed:
If anybody does know one, any help is appreciated.
Thank you very much.
Kind regards.
This is completely a different continent for me (we have just the nominate), but a searched found https://www.jstor.org/stable/3218455
For me, it’s new too, but I saw that some occurences in neighbouring countries have been confirmed by herbaria specialist, so it could be, that it is just overlooked. I would like to dive a bit in it and compare our plants.
The key in the Zika 2003 paper that @vladimir_fuka linked contains all the subspecies in your list except ssp. laxus. So as long as you have a description of laxus to work with, you should be able to sort through your plants. I can’t tell from your post where “our plants” are, except for what looks like German text in your list. So maybe you are in Europe?
Yes, I’m in Switzerland.
The key mentioned in Brittonia Volume looks well understandable. For ssp. laxus I’m still missing one.
Well, if you know how to use a key (and it sounds like you do), you can use the one in Brittonia (Zika 2003) to get partway to an answer. Use the Zika key to key out the plant in your hand. If it gets you to one of the four subspecies included, it is probably either that subspecies or ssp. laxus. Your next step is to compare your plant to laxus and the subspecies the key gave you. Read the descriptions of both taxa and see which one fits better. Bring a specimen of your plant to an herbarium with examples of both subspecies and compare them visually. Dichotomous keys are artificial constructs and are usually based on average or typical representatives of a taxon; they do not work perfectly with every plant. And they are often just a starting point to suggest what you might have.
Fun to see my friend Peter Zika mentioned here. He studied the Juncus effusus group over several years. A surprise to me was that the leaf sheaths, located near the base of the plant, are more useful than the flowers for identification. This is apparently a surprise to most iNaturalist observers, who post photos of the inflorescence, not the leaf sheaths; these observations usually can’t be identified to subspecies or (in many cases) even to species.
POWO maps Juncus effusus ssp. laxus from southeastern Africa so I figured most of us can ignore it. However, it’s been found the the Canary Islands where it must be introduced. If it traveled that far, it could be anywhere. I’ll have to learn more about it, unfortunately.
It’s true that keys are based on typical specimens, but the range of variation is often acknowledged in constructions like “leaves (3.5)4.5-6(7) mm” [long].