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I enjoyed this article. I now have names for a few euphorbs I either have or have had, or have seen, thank you very much for that. I've read that E. Symmetrica is classified as a subspecies of E. Obesa, which makes sense to me, since they are so very similar in appearance. So it should be labeled E. Obesa ssp. Symmetrica. Don't you love the way botanists keep changing names ? I wish any of the plants you list were hardy enough to live outside in zone 6, but no such luck. A few leafy types do survive our winters though.
Using the word spines when describing these plants is misleading, though it's pretty common. Botanically, the armaments they often bear are properly called thorns, and on euphorbias they usually appear in pairs on the edges of the angular stems.Many euphorbs, like Obesa or Tirucalli, for example, are thornless. But on plants where thorns are present I find it very easy to tell a euphorbia from a cactus, where I have doubts, simply by looking closely at the thorns. To me, even the tiniest thorns on a euphorbia look rather like rows of steer's horns, while I've yet to see any cactus spines that reminded me in any way of cow's horns. Fishhooks, maybe, but not horns. Another difference between them is the white sap of euphorbia. It's rather like latex, and can be very irritating to skin. Being under pressure, the white sap runs out quickly from any least amount of damage, as almost anyone who has handled one of these plants knows, and then dries almost like a scab over the wound, and often in drippy streaks down the stems too. It likely evolved as a means to defend the plants from being eaten. So far as I know, there are no cacti that have white sap, and I have to say I've never seen a wounded cactus bleed their sap anywhere near as vigorously as euphorbs do. Then, I've never tried to wound one just to see how it bleeds either :-). If the plants have flowers, that's another way to tell, because none have flowers anything like cactus do. On many the flowers are nearly invisible, they're so small. No showy petals, though some have coloured bracts, like E. Millii or, for that matter the ever popular poinsettia.
The greyish coloured, spiky looking bits sticking out from the sides of many of the plants pictured are neither thorns nor spines, and I have often wondered just exactly what they are, botanically speaking. One plant I had, ID unknown, I'm afraid, came loaded with these structures, but nearly all of them simply came off over time. They would often sort of bend down and almost fall out, at or just below skin level, or just come off if I brushed against them when watering. I noted that the plant very seldom bled any sap when they came off, so I thought they might be remnant structures from earlier flowers, though I am not at all certain of that. But I wondered, because a broken thorn always bleeds sap, just like broken stems or wounds do on euphorbs, and those greyish things don't seem to, which suggests to me that they are no longer a living part of the plants. Anybody know just what they are ?
E. millii is a great example for observation of the thorn's cow horn shape and their ability to mess up your clothes or your skin if you are careless handling these plants, and the typical euphorbia flowers. If you look at the middle of the coloured bracts that we usually think of as the flower, you will see the true flowers, quite tiny, which often look rather yellow, though I think most of us would need a magnifying glass to see much of their details. All in all, some of my very favourite plants are in this group of succulent euphorbias, and I always enjoy seeing them written about.
