Well, I learned it's a yucca plant, and the reason it hadn't grown that stalk before is that yucca has a freakish life-cycle: In order to blossom (that's why the stalk), it has to be eaten by little moths.
Nature is freakish.
Anyhow, here's the end-result: beautiful blossoms!
Note: The picture doesn't do it justice. Looking at it now, it seems unspectacular; I should take another shot with me standing beside it to show scale.