The Shamrock, contrary to expectations, cannot be said to be a specific plant. It is of course a kind of clover but which one? People writing about it frequently state that it is generally accepted that the most likely candidates are the species Trifolium dubium (variously called Lesser Trefoil, Suckling Clover, Little Hop Clover and Lesser Hop Trefoil; Irish: Seamair bhuí), with yellow flowers or the white-flowered Trifolium repens (White Clover; Irish: Seamair bhán). But which one? Well, excuse the pun but take your pick.
Generally accepted by whom? One supposes by botanists and Irish folklorists but those sites rarely supply a reference. However, amateur botanist and zoologist Nathaniel Colgan (1851-1919) asked people from around Ireland send him specimens of what they believed to be an Irish shamrock and identified the five most common plant species, of which the two most common were the yellow clover followed by the white. A hundred years later, Dr Charles Nelson repeated the experiment in 1988 and found that yellow clover was still the most commonly chosen. According to Wikipeida, yellow clover is also the species cultivated for sale in Ireland on Saint Patrick’s Day and is the one nominated by the Department of Agriculture as the “official” shamrock of Ireland.
The word “shamrock” is an Anglic corruption of the Irish seamróg, itself a contraction of seamair óg, meaning a sprig of young clover. The Irish shamrock is usually the species Trifolium dubium (lesser clover; Irish: seamair bhuí), with yellow flowers or the white-flowered Trifolium repens (white clover; Irish: seamair bhán).
A trawl through the internet looking for images of shamrock plants throws up a bewildering multiplicity of images of trefoil plants, the only thing they have in common being that they are (mostly) green. It soon becomes apparent that many of the images are taken from a different genus, that of oxalis, usually the one named wood-sorrel (Oxalis acetosella) in English-speaking Europe1.
People today should know better. Edmund Spenser, an anti-Irish colonist and commentator on Irish culture, also poet and ancestor of the late Princess Diana, reported the Irish eating shamrock and so have some other colonial observers but almost certainly what they observed was the Irish eating the wood-sorrel – in Ireland it has some common names associated with eating. Spenser and other colonists can be blamed for many things but not that confusion – they were not botanists and did not have access to the Internet. Also, seamsóg, the Irish name for wood-sorrel, does sound a bit like seamróg, especially if one is not listening carefully. The confusion can be continued in English, where the common sorrel (Rumex acetosa) is a completely different plant and a common enough culinary one.
Many species of the genus oxalis close their leave sand flowers at night – a handy trick which the trifolii do not have; indeed, try as they may, trifolii could not possibly close their flowers since each one is in the form of a cluster, while those of oxalis tend to be trumpet-shaped.
The wood-sorrel grows typically in woods which are shady but not too dark and is characterised, as with many other oxalis, by an acidic taste in the stems. As children in the area in which I grew up in south Co. Dublin we chewed the stems of a cultivated species with large green leaves and pink flowers, commonly grown in window-boxes and gardens and known to us by the name of “Sour Sallies”.
The shamrock (both varieties of trifulium) grows best in meadows receiving a fair amount of sunlight, in among grasses. It belongs to the clovers, a different family completely from oxalis, belonging in turn to a very large group of plants as different in appearance from one another as peas and beans on the one hand and furze (also known as gorse) on the other (but many bearing fruit pods). They are the legume group, plants that concentrate nitrogen in nodules around their roots, making many of them good crops with which to precede plants that require a lot of nitrogen, such as the cabbage family or cereals.
The expression “in the clover” as an idiom for being successful or having a good time alludes to the alleged fondness of grazing animals for the plants but this is much more likely to be the white clover, Trifolium repens (Irish: seamair bhán) than dubium, as the former grows bigger and thicker. Clovers are important plants not only for grazing animals and nitrogen-fixing but also for bee-keepers, being rich in nectar and pollen.
1 In North America, Oxalis montana is also called “common wood sorrel”.