| Tree Name | Somerled, Lord of the Isles | |
| Individuals | 14 | |
| Families | 9 | |
| Sources | 18 | |
According to the DNA test results of various members of Alexander and MacAlister families in the United Kingdom, Ireland, North America, and elsewhere, the two families diverged from a common ancestor within the past several hundred years. Both descend from Somerled, Lord of the Isles, an 11th century king who was also the progenitor of Clans Donald and MacDougall. If you are carrying the name Alexander, MacAlister, or some another variant of these surnames, you are welcome to join the Alexander and McAlister DNA Projects which are currently being hosted by Family Tree DNA.
Other branches of the Alexander family that split off from the main lineage in Menstrie settled in Paisley, Renfrewshire, Scotland. One was known as the Alexanders of Blackhouse and Boghall, while another was called the Alexanders of Ballochmyle. The coats of arms for both families closely resemble the arms for the Earls of Caledon in Northern Ireland and Alexanders of Menstrie in Clackmannanshire, Scotland. This suggests that all four families likely came from the same part of Scotland where they probably shared a common heritage. The interesting thing about the Alexanders of Paisley is that they were first documented in 1413, about a hundred years before Thomas Alexander was recorded in Menstrie.
Alexander of Menstrie - Sir William Alexander, 1st Earl of Stirling. Arms: Quarterly, 1st and 4th, per pale, argent and sable, a chevron, and in base a crescent, all counterchanged; 2nd and 3rd, or, a lymphad sable sails furled and flags flying between three crosses crosslet fitchée gules for MacDonald. Crest: A bear sejant, erect, proper. Supporters: Dexter, an Indian with long hair, and a dart in his right hand all proper having a circle of gold on his head with a plume of seven feathers or and azure and around his waist a like circle of feathers; sinister, a mermaid with a comb and mirror all proper. Motto: per mare, per terras.
