When it comes to shamrocks, Lesser Trefoil the real deal
Shamrock has a long association with tradition, religion, myth and lore. It is said to have been a sacred plant to the druids and the number three had mythical associations with pagan deities. St Patrick is widely reputed to have dismissed the idea of a pagan triad and to have used the trefoil to explain the Christian mystery of the Trinity, that there are three separate persons in the one God just as the one leaf comprises three parts.
'Seamair' is the Irish for clover and, as everyone knows, 'óg' is the Irish for young, so shamrock is an Anglicised corruption of the Irish for young clover. Any immature clover plant with small leaves can be passed off as shamrock but by popular consensus the Lesser Trefoil Trifolium dubium is the real deal, the authentic article.
Technically, the shamrock has only one leaf. The three divisions are leaflets of the one compound leaf. A set of three leaflets is the norm but other numbers can turn up on rare occasions. The most common of these rarities is the famous, so-called 'four-leaved clover' popularly believed to bring the finder good luck.
It is believed that clovers with any number of leaflets other than three are probably mutations, rare errors that occur in the replication of DNA. Many mutations are fatal or damaging and are generally of little use to the individual involved. They are oddities of nature, like having a sixth toe, and there is nothing intrinsically lucky about them.
Four-leaved clovers are not that rare and have been successfully bred commercially for the production of lucky charms. Consequently, they are unlikely to be chance mutations. They appear to be caused either by a recessive gene appearing at a low frequency or by the interaction of several genes that happen to segregate in an individual plant.
Since the gene that determines that each leaf is divided into three leaflets is dominant in all clovers, genes for any other number or combination of leaflets tend to be normally masked and to appear only as rare chance events.
Shamrock and other clovers produce seeds in pods evidencing that they all belong to the large pea family. The pea flowers are characteristic of the group. Lesser Trefoil normally flowers from May to August. Its flowers are pale yellow in colour, each is borne on a short stalk and they clustered together in a flower head of a dozen or so individual flowers.