No. There is a species of Euphorbia on Mt Elgon (Uganda/Kenya) which grows to 30 m (E. obovalifolia)

Hi

Euphorbia milii (crown of thorns, Christ plant, Christ thorn) is a species of flowering plant in the spurge family Euphorbiaciae, native to Madagascar. The species name commemorates Baron Milius, once Governor of Réunion, who introduced the species to France in 1821. It is suspected that the species was introduced to the Middle East in ancient times, and legend associates it with the crown of thorns worn by Christ.

these articles and sites will help you:

http://en.wikipedia.org/wiki/Euphorbia_milii

http://en.wikipedia.org/wiki/Euphorbia_resinifera

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0CDcQFjAE&url=http%3A%2F%2Fdeepblue.lib.umich.edu%2Fbitstream%2Fhandle%2F2027.42%2F97788%2Fbdorsey_1.pdf%3Fsequence%3D1&ei=wbkGVJaBN8XpaJ-tgZgI&usg=AFQjCNHE3f9ZSzGubuw2tNWQIBQYNc6SfQ&sig2=VcemlTi84E6baaxrUnNBKA&bvm=bv.74115972,d.d2s

Difficult to say. East African Euphorbia candelabrum has about the same size and sometimes well exceeds 10 m.

Euphorbia tetragona and E. triangularis go well beyond 15 m in South Africa. I suspect in East Africa you will find other species in excess of 20 m.

No. There is a species of Euphorbia on Mt Elgon (Uganda/Kenya) which grows to 30 m (E. obovalifolia)

Relatedly, there was in interesting publication on diterpene biosynthesis and gene clusters in the Euphorbiaceae.

http://www.ncbi.nlm.nih.gov/pubmed/25172144

in western Mexico, the tallest Euforbia I know is E. Tanquahuete, 12 m tall.

In the Canary Islands and Madeira we have one arboreal and arborescent endemic species, Euphorbia mellifera, which can reaches occasionally up to 15-18 m in the wild. This taxon grows in the humid laurel forest and is not similar to the Arabian Euphorbia showed in the images, as belongs to a different section of the genus and it's a close relative of E. stygiana, endemic from the Azores islands. 

E. candelabrum can reach that height too, over 10 m. 

Euphorbia cooperi  found in South Africa also attains height of 10 meters.