Euphorbia heyneana

Three prostrate species are rather close. I found the following keys in Flora of India:

30 a. Plants prostrate, only branches or tips of branches decumbent; cyathia solitary, paired or 3 together … 31
b. Plants erect, decumbent or ascending; cyathia more than 3 in glomerules … 33
31 a. Stems and branches pinkish grey; mature capsules remaining within the involucre … 32. E. thymifolia
b. Stems, branches and leaves green, glaucous-green, purplish green or blackish green; mature capsules protruding out from the involucre 32
32 a. Stems, branches and leaves blackish or purplish green; capsules acutely keeled, with ciliate hairs confined to keels only … 26. E. prostrata
b. Stems, branches and leaves green to glaucous-green; capsules obtusely keeled, glabrous or sparsely hairy all over the surface … 13. E. heyneana
33 a. Plants glabrous; leaves linear-lanceolate, 3 – 6 mm wide, glabrous to sparsely pilose … 17. E. hyssopifolia