I don’t know much about this, but we do have a couple of fairly rare specimens at the nursery right now. It’s called Cucumber Tree because it is. A tree, and a member of the cucumber family. The only tree in the Cucurbitaceae family that includes melons, squashes and cucumbers, but not the only succulent member. There’s also this other caudiciform we carry, the better known Ibervillea lindheimeri.
Dendrosicyos is a monotypic genus in the Cucurbitaceae. The only species is Dendrosicyos socotranus, the cucumber tree. The species is endemic to the island of Socotra in Yemen, and is the only species in the Cucurbitaceae to grow in a tree form.
Would you like to see an old-timey photo of the tree in habitat in Yemen courtesy of Wikipedia?
Now would you like to see a closeup of the leaves? Here you go.
They do look a bit like squash leaves!