The 18 letters that make up the Gaelic alphabet were traditionally named after trees and other plants. The trees were used to help teach children their alphabet.

Ailm Elm
Beith Silver birch
Coll Hazel
Dair Oak
Eadha Aspen
Feàrn Alder
Gort Ivy
Uath Hawthorn
Iogh Yew
Luis Rowan
Muin Vine
Nuin Ash
Onn Gorse
Peith Downy birch
Ruis Elder
Suil Willow
Teine Furze
Ura Heather

The ancient Alphabet of the Gaels contained sixteen letters

In the primitive Gaelic Alphabet H and P were not included.

The letters of the Gaelic Alphabet were named after shrubs and trees: the name of the letter, in every instance, save that of the aspirate H, begins with the letter itself; to preserve, as it were, its proper sound or power.

The sixteen letters of the ancient Gaelic Alphabet were arranged in the following order: B L F S N D T C M G R, and A O U E I. The H and P have since been added; so that the modern Gaelic Alphabet consists of eighteen letters, arranged as follows: A B C D E F G H I L M N O P R S T U.

Beginning with A, the names of the letters of the modern Gaelic Alphabet are: Ailm, which means the fig or palm tree; Beith, the birch tree; Coll, the hazel tree; Dair, the oak tree; Eadha, the aspen tree; Fearn, an alder tree; Gort, the ivy; (H) Uath (the name of the aspirate h), the white thorn; Ioga, the yew tree; Luis, the wild ash; Muin, the vine tree; Nuin, the ash tree; Oir, the broom tree; Peith, the dwarf elder; Ruis, the bore tree; Suil, the willow tree; Teine, the furze or whin bush; Ur, the heath shrub.

There is no K in the Gaelic Alphabet, ancient or modern; nor had the ancient Latins any character like that letter: they gave the sound of K to C, as in the word sacra (pronounced "sakra"), where the c has the sound of the English letter k. The Latin name Caesar is now in English pronounced "Seasar" (where c has the sound of s); in German, however, it is pronounced "Kaiser;" but in no case can C, in Gaelic, be sounded like S. Nor have the Greeks the letter C in their Alphabet; but K (the Greek letter "kappa") corresponds to the Gaelic and Latin C, which has or should have the sound of the English letter K.