Tree of Life, Revised

Tree of Life

Not too long ago, there were three branches to the tree of life:

• Eukaryotes, which are all the things that have a macroscopic existence,
• Bacteria, which are everywhere but too small to see without a microscope, and
• Archaea, which are bacteria which live in places were no normal kind of life can live.

There were three branches and all was well. But then some wise guys started poking around, stirring up shit, and found that there were a hell of lot more bacteria than they had realized. Now someone has condensed all this new data into this drawing and we find the part that we consider important, the part that contains us and all our animal friends, is just this one branch growing off to the side. Just goes to show that if you make enough microbes eventually one of them will grow up to be somebody. Story in The New York Times. Via Detroit Steve.

Meanwhile, back at the ranch, I don't understand the key on this drawing, to wit:

Major lineages with isolated representative - italics
Major lineage lacking isolated representative - (red dot)

I can understand having an isolated representative of a particular thing, and I can understand having a representative of a group or class of things, but having an isolated representative of a big group doesn't make any sense to me. Does this mean you have a single representative of a large group, but it is isolated so we don't know if it is really representative or not?

And if we are lacking an isolated representative, does that mean we have no representatives at all? Or we have a whole bunch, but they are so different we can't call them representative?

I know microbiology has their own lingo, but these two lines need translating.