Euphorbia susan-holmesiae

– I would go with E. antiquurum, because the angles are distinctly 3-winged, the wings are running almost straight. In E. tortilis the angles are not that promently winged, they are lobulate with stout paired spines on lobes, and most importantly the angles are spirally twisted like we have in E. neriifolia where of course the angles are not that prominents, and there are 5 spiral rows.

– the young inflorescence appears green. once the ivary is formed it would impart the reddish/ purplish tone.

– ..  cleared my doubt on inflorescence colour.

– These plants are from the same locality. Kindly excuse me for mixing two species(?) in the same post. Please guide me in this morphology of Euphorbia spp.
   The previous plant posted have straight grooves and not that of E. antiquorum. Is this any physical variation or totally the species is different?

– .. , I happened to see E. antiquorum L. at Rani baug, Mumbai on 6 Feb 2011. Attaching the pictures of the one identifed by Dr. .. as l E. Antiquorum L. matching with type.  Just next to it is another species which
as Sir said goes as E. antiquorum, but it is not matching the type. Attaching that too for comparison.
To me both your sets do not match, but perhaps the second set is close to E. antiquorum.  Hope this helps!

– Here is the lectotype of Euphorbia antiquorum L. Lectotype : Herb. Clifford: 196, Euphorbia 1 (BM-000628669)
Designated by: Wijnands in Bot. Commelins : 97 (1983) You can clearly make out which is the real Euphorbia antiquorum.
   There is another species called Euphorbia royleana. Kindly check your plant with that description. I am not sure if this plant is found in South India but it is supposed to be widespread from Pakistan to Taiwan. I assume I have seen it in Uttarakhand as well as Rajasthan.

– Just wanted to add. Euphorbia is a very big group and one most interesting thing is, the genus Euphorbia has two type species, Euphorbia antiquorum and Euphirbia serrata. I never heard a genus with two types before. If anyone else knows then please do add to our information.
Kew has a list of around over 5000 names of which only ~2000 names are accepted. That itself depicts the taxonomic complications here.

– Your two sets of plants seem to be the same E. antiquorum , only the matter of older and younger branches: All have distinctly 3-winged stems with straight wings.
..  your first three plants are E. antiquorum without any doubt, but there is no reason to confuse the fourth photograph. It is without any wings and with spines which are spirally arranged. It should be E. neriifolia.
This key from Flora of China should help in separating often confused species

– Thanks for the detail. I totally forgot about neriifolia. If you look at the second group of pics shared by  …, I think there are two species. Secondly, in the lectotype, the wings are not straight. I have seen both of these plants myself in gardens, and I always thought one of them to be hybrid. But you are more experienced so you must be having a better idea.

– Perhaps this image should clarify what I meant by straight and spirally running wings. E. tortilis has spirally running and E. antiquorum straight.
Aridlands
If you look carefully the type specimen cited by you also has straight wings.

– Here is my photograph where you can see both young and old branches in the same plant.

– Thanks for sharing the pic and link. I understood what you meant. I just imagine if those contractions and swelling are due to environmental factors or that is a consistent character of this taxa? because that character is also evident in image of the Lectotype. Undoubtedly Euphorbias are complicated!!

– Yes …, the environmental factors might play a role in the morphology of this genus. From ..’s statement and ..’s pictures, its clear that this Euphorbia antiquorum have much variations. However the plant does not matches with E.royleana. What I had posted are young and old plants of the same species.

– Yes, I also think that just because of dryness the tip of these plants do get constricted and at the same time, the wings on the stem get constricted as well. But there are some taxa in Euphorbia and others too, in which such characters are genotypic. Hope you understand my point there. Yes the plant was not E. royleana. As I said before, I completely forgot about E. neriifolia.
Euphorbia is very complicated, jut put together Euphorbia thymifolia and Euphorbia cotinifolia and without flowers and latex, you dont find anything common!!