Trying to understand

Mosses are confusing enough. But Ma Nature likes to have us completely bewildered. So we have liverworts, which look like mosses, act like mosses, and grow intermingled with mosses. Our guide on the moss walk kept pointing out bits of green that looked like all the other bits of green, and calling them liverworts. Even with the hand lens I was carrying, I couldn't see the difference.

"And what is that one?"

Everything's somewhere on the web, if you look long enough. I found a site from Australia that explains the difference so clearly that even I can see it.

First, look for sporophytes, the spore-bearing capsules.

The green or red capsules are sporophytes, growing spores.

It's always possible, and very easy, to determine whether you have a moss, liverwort or hornwort if sporophytes are present. Remember that a sporophyte consists of a spore capsule, with or without a supporting stalk or seta.

Are groups of spore capsules held aloft on complex structures?
The bryophyte is a liverwort.

A fuzzy head, like a pussy willow or a grass ear, would be a complex structure. If the "moss" has those, it's a liverwort.

If the stem is translucent (and often colourless) the bryophyte in question is almost certainly a liverwort.

If the stalk supporting the capsule is opaque and coloured green, brown or red the bryophyte in question is a moss.

 If sporophytes are absent you'll naturally need to look at some gametophyte features, the first step being to see whether you have a thallose or a leafy bryophyte. A thallose bryophyte is either a liverwort or a hornwort. A leafy bryophyte is either a moss or a liverwort.

(Hornworts are aquatic; we can ignore them for now.)

If the plant has no clear stems or leaves, it is thallose, and therefore a liverwort.

The first thing to do is to see whether you have a thallose or a leafy bryophyte. The almost leathery thallus of a robust thallose bryophyte is fairly easy to pick. Similarly, in some leafy species the leaves-on-stems growth habit is very easy to see. 

For this, with some of the plants, we need a lens; some liverwort thalli look like stems and leaves to the naked eye.

So the photo above is clearly a moss. The sporophytes are simple, held on a tall stalk, with red tints. The leaves grow attached to the stems, not as continuations of the stem. (Look at the stem below the red sporophyte on the right.)

In the great majority of moss species the mature spore capsule opens by means of a well-defined mouth. Remember that a liverwort spore capsule never has a well-defined mouth.

To see that, a lens is probably needed. And being there at the right time, when the spores are mature, or already released.

There is much more info on the page I'm quoting, details on how to distinguish thallose from leafy structures, photos, and exceptions to the rules. (Aren't there always?) But the sporophyte detail is enough for a rough guide, for now, for me.

The moss is green and leafy; even in this photo, the stems are visible as a separate structure from the leaves. The liverwort is one of the leafy ones; the leaves are short and stubby. Luckily, it's red.