Herb trinity shams

• shamrock: the shamrock, an unofficial symbol of Ireland, is a three-leafed young white clover, sometimes (rarely nowadays) Trifolium repens (the white clover, known in Irish as seamair bhán) but more usually today Trifolium dubium (the lesser clover, Irish: seamair bhuí). The shamrock was traditionally used for its medical properties and was a popular motif in Victorian times. According to legend, St Patrick used the shamrock to demonstrate the mystery of the Holy Trinity to early Irish converts
  • Wikipedia

• Shem

• Holy Trinity: a mystery of Christian dogma whereby God has one divine nature but three persons; according to legend St Patrick used the shamrock in an attempt to explain this mystery to early Irish converts → Rock of Cashel (Munster)

Commentary

amaid her rocking grasses the herb trinity shams lowliness

This phrase identifies the third of Ireland's "five fifths" or provinces, Ulster, which includes Downpatrick, the resting place of Ireland's original pastor St Patrick.

Ireland has only four provinces today – Ulster, Munster, Leinster and Connacht – but in the early Christian centuries there were five provinces or fifths, the Middle Irish word coiced (Modern Irish: cúigiú) meaning both fifth and province. The fifth province was the royal province that included Tara, the seat of the High Kings of Ireland. It corresponds roughly to the modern counties of Meath, Westmeath and Longford, with parts of Dublin, Offaly and Louth, all of which are now considered to be part of Leinster.