namely, the fact that the wild mustard Brassica oleracea, once domesticated, produced a bewildering variety of vegetables by selecting each cultivar for a different part (cabbages from terminal buds, Brussels ssprouts from lateral buds, broccoli and cauliflower from flower buds, kale from leaves, and so on), all of them still being technically part of the same species, Brassica oleracea var. whatever.
Now, as far as I know, nobody has bred B. oleracea into a tree. But there is, not quite a single species, but a genus, that has gotten pretty close to that kind of internal morphological diversity:
Behold Euphorbia, the genus of spurges, counting over 2000 species (that nevertheless are often capable of interbreeding) scattered throughout all continents:
Euphorbia dendroides (Mediterranean)
The poinsettia, Euphorbia pulcherrima (Central America)
Euphorbia actinoclada (East Africa)|, one of the many cactus-like species (cacti proper are all American species except one, so if you see a cactus-like plant in an African or Asian deserts, odds are it’s actually a kind of euphorbia)
