[rally]

A 300mm lens can also be a macro lens !

The two terms (300mm lens and macro lens) are not mutually exclusive.

Adding to Dennis' comment - a true macro lens is supposed to have at least a 1:1 subject to image size ratio.
However it can be greater and in some cases lens manufacturers will label a lens "macro" even if it doesnt quite meet that criteria.

Generally a macro lens will have the ability to have a very short focus distance, which therefore increases the size of the subject on the image plane irrespective of focal length.
So some lenses are labelled "macro" because of that feature.

You can take macro photographs with all sorts of different focal length lenses.

Sometimes its good to be able to get within mm's of your subjects and create interesting perspective macro shots, other times you need a long focal length lens to get even close to insects on the move - eg dragonflys and butterflies.

Some of my favourite shots (of insects) were taken with a 400mm effective focal length lens. Its a 50-200mm zoom with 2x crop factor (4/3rds format CCD).

Sometimes I add a Canon 500d macro lens to the front of this lens (not to be confused with a camera - its a doublet) or a MCON35 Olympus macro adapter, and 1.4x adapter and that allows me to get a lot closer to the subject

Yet other shots have been taken with a rectilinear 7mm lens or a 35mm lens with 2x adapter and twin macro flash for getting really, really close to bugs.
You have to watch the front element doesnt actually touch them.

By changing focal lengths you also change your depth of field - so a short focal length lens will have a hyperfocal distance which is very short, meaning the bug and everything behind it are in focus, whereas trying that with a longer focal length lens and you might find the bugs eyes are in focus and the rest of him forward and back are out of focus - that is the advantage of using a macro flash and a tiny small aperture

So you lens choice can really change dramatically depending on the type of macro photography you wish to do and what sort of lighting you have.
eg if your macro is coin faces or polished rock faces you dont need much depth of field - however if you want a full frontal of moth with long antennae and you want most of him in focus back to his wings and tail - you're in trouble !

Sorry to complicate the matter !

Rally