Does injera require a starter?
The traditional Injera is made with wild yeast. Basically, you mix the ingredients and let it sit for 2-3 days to ferment. The wild yeast just finds it, and it works fine. However, the time it takes to ferment changes based on the average presence of yeast in the air and things like that, so it changes from batch to batch.

As a shortcut, and mostly for consistency of results, you can use a sourdough starter. In fact, once you've made your first batch, you can keep an Injera starter, so that you're still just using Teff flour.

To be fair, the biggest factor in fermentation time is usually the ambient temperature, rather than the source of the yeast.