It does look like a guava seedling. I'd let it grow out and see what happens. Do you have any wild strawberry guavas around your house? Could be one of those.

No, I haven't seen any strawberry guavas growing wild around here. I do have a few strawberry guava seedlings that I got in the winter or spring, but they haven't produced any flowers or fruit. The only guavas I've bought fresh were the Mexican cream guavas, and I took the seeds and planted them in various places. So, if it's a guava, it'd have to be that type.

A few more things to ID. Any ideas?

This plant has something like a segmented trunk, like grass, bamboo, sugar cane, and these white flowers at the top.
This one has nettle-like leaves, but they don't sting. If you touch any of the plant, it gives off a pretty pungent odor on your skin if you touch it. The 'trunk' is sort of square, and it can be either green or purple, or both, but the trunk also has like a v-like shape or indent on each side, all the way down it.

2 pics of another unknown plant. This one popped up in my raised beds, and I'm not sure I've ever seen it growing wild in my yard before. So, it could have been brought in with some plants or soil.

Did I stump everyone with my swamp muck, acidic, low-lands weeds?

The one with the tiny white flowers is alligator weed.

#2 looks like so-called swamp milkweed. I always call it marsh milkweed because swamps are wooded wetlands, whereas this nice herbaceous plant would likely be found in a marsh. Nit-pick much?

#3 looks like a spent inflorescence of lavender, but sure could be a lot of other things.

#4 is one of the smartweeds. There's only about 1000 species of smartweeds that can be found in N. America so that's as much as I want to try to unpack that, but for sure, it is one of these.

#5 is on the tip of my brain, but I guess for now, that's where it shall stay, darn it. It's an easy one too!

That's all I got for now.

edited to add: #1 looks like a start of Iochroma, but uh..........I would not warrant that ID.

Thanks for the help. As far as the one with white flowers being alligator weed, the flowers don't match up. The flowers on alligator weed look closer to clover flowers, while this one has flowers that are more similar in appearance to dianthus. The leafs appear to be smoother on alligator weed too, without the little serrations or teeth.

As for the smartweed, I looked it up, and saw some very similar plants, especially water pepper. I see it's listed on green deane's website as a pepper supplement and as an herb, for intestinal issues.

Is there any type of wild lavender that grows in Florida at all?

Xen, re-looking at that one that I said reminds me of lavender, it too could be one of the smartweeds. There are many! And yes, water pepper is a well-known example from this tribe. All smartweeds, even the non-native types, are considered good food plants for ducks and such. I like them.

And another one. This popped up in a container. Not sure if it's something I planted or not.