Agave or Aloe?

When is an Aloe not an Aloe? When it's an American Aloe, or Agave.

Agaves and Aloes certainly look similar, but despite the fact that Agave americana is often called by the misleading name of American Aloe, the two plants are not actually closely related. The agaves are native to Mexico and the southern states of the US and come from the Agavaceae family, while the Aloes are African in origin and part of the family Asphodelaceae.

Why am I bothered? In my last post I described a plant which I'd seen in Barcelona as an aloe, but in a comment, Blackswamp Girl referred to it as an agave. Which got me wondering if I was right.

After looking at lots of pictures on the net, I think I am. But I can see why the confusion arises. There are agaves which look very similar to this, and aloes which are quite different.

What does anyone else think?