While you're waiting for Frank, Jordi...I'm going to guess Euphorbia guerichiana.

~Rosemarie

Hi Jordi,
sorry for the delay. I've been quite buisy this week.

Rosemarie's guess on this Commiphora-like Euphorbia isn't bad. E. guerichiana occurs in Namibia, builds shrubs up to 2 m or trees up to 6 m, stem up to 30 cm in diameter with paper-like bark, branches erect, about 3 cm in diameter.
Maybe trouble causing are the leaves of your plant. According to literature the leaves of guerichiana are obovate to lanceolate, 3 to 6 mm and more long, 1.2 to 2.3 mm in diameter, apex rounded, base cuneate, margins entire, light green to blue green, minutely puberulous when young on both sides, with green or pale red petiole of 0,25 to 4 mm in length, deciduous.

To me the leaves of your plant look somewhat larger than described, but I'm uncertain about the true sizes.

Frank
www.euphorbia.de

Rosemarie and Frank,

Thanks for IDing. I am pretty sure you are right. Maybe the leaves are a little bigger due to the more humid climate and less full sun here than in habitat.

Jordi