This for me is a very exciting plant because I obtained it 'accidentally' thinking it was just a small Aloe barberae, and indeed for many years these were thought to be a different form at that species. Then, once biologists realized it was NOT Aloe barberae (flowers were obvious very different) it was given the moniker Aloe Medusae, though I do not know the origin of that name. So for another 6 years I had in my collection an Aloe Medusae. And then someone finally found it in Mozambique and officially described it. Since then it has been found in South Africa as well. So now I had a whole new species of plant, and by this time it was flowering and had grown over my head, including a cutting I made from it.
This is a large, single stemmed by highly branched tree aloe very similar looking to both Aloe barberae and Aloe eminens. However, after seeing hundreds of these, I now can tell them apart from the A barberaes pretty easily even without flowers (still not 100% of the time, though). Aloe barberae is a much more heavy-bodied plant while Aloe tongaensis has thinner, longer, more delicate branches, and leaves never start out has massive as they do in Aloe barberae, despite their nearly identical overall shape and consistency (rubbery and very bendable, moderately to deeply channeled with small, light, marginal teeth). In fact, leaf size and width alone is one of the best indicators that Aloe tongaensis is not just another Aloe barberae. Eventually Aloe barberaes develop into massive trees, something which Aloe tongensis seem reluctant to do (only growing up to maybe 15' tall), and trunk diameter, though pretty thick, pales compared to those of mature Aloe barberaes.
Flowers are the primary distincitve features, growing on short multi branched inflorescences, and topped with short, almost capitate racemes of yellow-orange flowers, all facing up until opening at which time they drop downward (this is nothing like an Aloe barberae inflorescence). Aloe barberae inflorescences are extremely stout, short structures having maybe 2-3 branches at the most and flowers are densely packed, non-drooping and pinkish red. The flowers on Aloe tongaensis also always seem to be reaching for the sky, often far above or at least noticeably above the vegetation (something else one never sees in Aloe barberae inflorescences).
Cultivationally the two are very similar, however, with both being among the most cold sensitive of all the aloes, reluctant to die from freezing, but badly damaged at temps below 28F (Aloe tongaensis seems a bit tougher in this respect). Both love lots of water all year round. Both are also huge aloe mite magnets.