I looked up all the entries for Euphorbia abyssinica & Euphorbia acrurensis in the Euphorbia Journals but there wasn't any useful information. The consensus is that they are all the same plant. But personally I think they look way to different. So I'm labeling mine E. acrurensis.
Here's a good conversation about these plants. Palmbob is very knowledgeable and he's still confused.
PlantFiles Pictures: Desert Candle (Euphorbia acrurensis)
Euphorbia abyssinica synonyms:
Euphorbia abyssinica var. erythraeae A Berger
Euphorbia abyssinica var. tetragona Schweinfurth 1899
Euphorbia acrurensis N.E.Br. 1912
Euphorbia aethiopum Croizat 1941
Euphorbia candelabrum var. erythraeae A. Berger 1907
Euphorbia controversa N.E.Br. 1912
Euphorbia disclusa N.E.Br. 1912
Euphorbia erythraeae (Berger) N.E.Br. 1912
Euphorbia grandis Lemaire 1857
Euphorbia hararensis Pax 1907
Euphorbia neglecta N.E.Br. 1912
Euphorbia neutra A.Berger 1907
Euphorbia obovalifolia A.Richard 1851
Euphorbia officinarum var. kolquall Willddenow 1799
Euphorbia richardiana Baillon 1860
source for synonyms:
Euphorbia abyssinica