Carran is the traditional Gaelic name for scurvy grass, a bitter-sweet relative of the cabbage (not a grass at all), but refers to more than one species. It was broken down into a number of specific names including carran sassanach - English scurvy grass, carran ailpeach - Pyrean scurvy grass, carran an t-slèibhe - mountain scurvy grass, and carran albannach - Scottish scurvy grass. It is an edible, flowering, seaside plant, rich in vitamin C, widely used in the past as a valuable antiscorbutic medicinal ingredient, when scurvy was the scourge both of seafarers and ill-fed landsmen.
The first-century writer Pliny the Elder (A.D. 23–79) writes in his Naturalis Historia (Natural History) about a disease suffered by Roman soldiers in Germany. Their symptoms resemble those of scurvy, and Pliny recommends a Herba britannica, which has been suggested to be scurvy-grass. Martin Martin mentions stumbling across a rich depository of scurvy grass during his journey through the Hebrides in the late 17th century:
'This rock affords a great quantity of scurvy-grass of an extraordinary size, and very thick; the natives eat it frequently, as well boiled as raw; two of them told me that they happened to be confined there for the space of thirty hours, by a contrary wind; and being without victuals, fell to eating this scurvy-grass, and finding it of a sweet taste, far different from the land scurvy-grass, they ate a large basketfull of it, which did abundantly satisfy their appetites until their return home. They told me also that it was not the least windy or any other way troublesome to them.'
M. Martin, 1703 'A Description of the Western Islands of Scotland, circa 1695'
Apart from its medicinal values, scurvy grass was also used by the more adventurous 18th century brewers, who incorporated scurvy grass as one of the many other original ingredients (like i.e. cowslips, brambles, elderberries, birch, pine leaves, horehound and carrot seeds) into their ales.
Resources:
'Flora Celtica, Plants and People in Scotland' - W.Milliken & S.Bridgewater, 2013
'Healing Threads, Traditional Medicines Of The Highlands and Islands' - M.Beith, 2018
'New Flora Of The British Isles'' - 2nd edition, Clive Stace, 1997
'The Orkney Book Of Wildflowers' - Tim Dean & Anne Bignall, 2019