Examining the Legitimacy of a "Clan Muir'
The claim is that Clan Muir is a Scottish clan that is armigerous (it has no chief recognized by the Court of the Lord Lyon). While some members of Clan Muir claim it as an independent clan rooted in Ayrshire and the surrounding area, some, in Ayrshire, are believed to be of a sept of Clan Boyd.
This being said, and despite an effort made by several, in more recent years, suggesting Clan Muir is an ancient clan, in fact, it appears to post-date the 18th century, and may well be a 20th century creation (if anyone has primary source material to the contrary, that shows the phrase "Clan Muir" prior to the 19th century, please let us know). There is no record, or "history" of the supposed clan, documented to any primary resources, prior to the 20th century. Further, as Lowland Scots, it's highly unlikely that such a clan existed prior to the 19th century. Perhaps the most glaring reality of the matter is that, in his reflections on the Muir line, in Historie and Descent of the House of Rowallane, Sir William Muir (1594-1657) makes no reference, whatsoever, to a clan system for the Muir family. Additionally, while the book was not published until 1825, the written work itself was produced prior to Sir William Muir's death in 1657. There is no written history of the Muir line known to exist prior to the publication of this work.
Nonetheless, even as a late 19th or early 20th century creation... there is a registered tartan... not to Clan Muir, but (as per the official Tartan Registry) to "Muir and Moore". If there is any legitimacy to a Clan Muir, and the claim of ties to the history of the Muir/Mure/Moore lines from Southwest Scotland, then a distinction must be made as to those who can claim an affiliation.
The Muir tartan, is, in fact, registered as the "Muir/Moore tartan", with no mention of it being associated with a "clan". It has the traditional blue - black - green base, but with an unusual motif of three narrow red stripes appearing twice on the green square. A similar device is seen in the Cochrane tartan. The threadcount of this illustration comes from a sample in the collection of John MacGregor Hastie, who collected tartans between 1930 and 1950, and whose work formed the basis of the archive at the Scottish Tartans Society. The tartan was documented in John Ross's, Land of the Scottish Gael (1930). Samples in Scottish Tartans Authority Dalgety Collection. Per the Scottish Register of Tartans (2009) , the date of this tartan is 1 Jan 1880.