My mother's family - direct line is Ferguson, a derivative from Fergusson. The family line contains a mixture of Scots, Irish, Irish-Scot and Scot-Irish. However, as in all families the line tends to blur at places.
Contrary to popular belief there is no such thing as a formal clan. In fact the modern idea of clans, tartans and clan chiefs are all based on Victorian ideas, made popular by Sir Walter Scott. The formal dress that many Scots wear to weddings is based on designs by Sir Walter. Lets face it, its good for Scottish tourism, and is building an idea of unity to the modern Scots.
Having said all that, this researcher has in some ways fallen in with the popular myths, for instance Ferguson Clan (if there be such a thing) does have its own tartan, and also a clan crest.