In Scandinavia, which is nearly as potato-heavy as Ireland, turnips were a primary staple crop before the potato came around, so much so that in much of the world the rutabaga, a large version of the turnip, is known as a "swede". I would be surprised if this was not the case in pre-1600s Ireland as well.
FWIW, in nearby Scotland "neeps and tatties" (turnips & potatoes) is still the canonical accompaniment to haggis.
> the rutabaga, a large version of the turnip, is known as a "swede".
And "rutabaga" is from "rotabagge", the dialectal word for turnip in the region of Småland, from where the majority of Swedish immigrants to North America came (over 1 million Swedes emigrated to North America in the second half of the 19th century).
Germany chiming in ... We have something that is called "Rote Beete" (eng: beet root) which sounds similar to "rotabagge" (eng: rutabaga), but apparently is a different plant.
It sounds alike but is different. The vegetable has the same name in Swedish, rödbeta (literally red beet, which makes sense since it's deeply red).
Rotabagge is something like "root bug", but where the bagge/bug part is more like an old/dialectal word for "lump", I think.
Edit: "bagge" is likely to have the same root (no pun intended) as bag. After looking up a few of these different roots on wiktionary, it could be that the have common roots but have just been mashes up through the millenia. The etymology seems unclear,and they have similar enough gibberish names in lots of different languages (beterraba, beterraga, etc).
It is actually somewhat suitable. Not only because "små" means small in swedish.
But also because the 1800s version of the ball-pit consisted of lots of round pebbles, put there particularly in Småland by some evil ice-sheet-wielding mastermind, that the kids played with by carrying them from the barren Smålandish fields.
Actually, it's kind of the other way around: IKEA, and Ingvar Kamprad, its founder, are from Småland. He started selling matches as a young boy (connecting to another Swedish business empire of yore, Swedish Match and its founder Ivar Kreuger).
IKEA is an acronym: Ingvar Kamprad, Elmtaryd, Agunnaryd. Elmtaryd was the Kamprad family farm and Agunnaryd is the nearby village.
My father-in-law is from the very same area in Småland as Kamprad, and they were born the same year.
In Germany some less digestible Inulin rich roots were also commonly used before the potatoe became ubiquitous like the Jerusalem Artichoke (which also was imported like potatoes). Now they are mostly used to produce alcohol. Scorzonera are still quite popular.
FWIW, in nearby Scotland "neeps and tatties" (turnips & potatoes) is still the canonical accompaniment to haggis.