Surprisingly there are several tropical root-crop plants well suited to frost free or better warm glasshouses. Probably the best value are Colocasias as many of the same family are already valued glasshouse specimens. Sold in Ethnic shops and some supermarkets these are known as Cocoyams in Africa, Taro in the Far East, Dasheen or Eddoes in the West Indies. Even more confusing there are the admittedly rather similar though usually larger growing Xanthosomas Cocoyams, also known as Tannia and but Eddoes produce many small tubers and the others are more like Dasheen with single larger ones.
Cultivars of all of these are grown worldwide both ornamentally and for their leaf or tuber as crops, though generally, outside Africa, Colocasias are preferred to Xamthosomas. (Then there are actual Yams, a variable group from the Dioscorea family. Most real yams are not such good value in containers being large rambling climbers slow to crop, interesting though and worth patience.)
With any Cocoyam you can plant small tubers or bulbils, but if you can only get large tubers then a large piece from the top can be made to shoot given a bit of bottom heat and then grown on. Kept warm and in only weeks you can have enormous gorgeous shiny green arrow shaped leaves on metre high stems, imposing foliage plants.
Also often called Yams by Americans, especially in the Deep South are Sweet Potatoes. These Ipomoeas have similar foliage and tubers to true yams but are faster and heavier to crop, and with attractive flowers as well. If you plant their tubers or pieces though these nearly always rot, instead force a tuber to shoot in gritty compost in real warmth. Then detach the shoots when finger length to pot on, still in warmth, later moving them on into large containers with canes to twine up. The lush foliage can be tinged purple and also eaten as spinach.
There are several other S. American tuberous crops worth experimenting with. Oca, from the Oxalis family, makes clover like plants, Mashua grows much like it’s relative the Nasturtium. Sadly neither yield well here. However Yacon, a relative of Jerusalem Artichokes is so easy, and productive it’s a must. For a near instant show of healthy verdant foliage, to a couple of metres either way in a large container, just plant a tuber and stand back.