Petroselinum crispum, an herb both savoury and ornamental, in some cuisines seen fit to be a principal ingredient, as in tabbouleh; in some to be a key seasoning, as in its role as a component of a bouquet garni and as one of the four axiomatic herbs of English folk-song; and in some to be a garnish appended to a plate of steak and tomato and returned to the kitchen most often uneaten, therefrom perhaps to be recirculated.
Petroselinum has nothing to do with selenium but one thing to do with petroleum: the rocks of the Greeks. Its etymon is πετροσέλινον, petroselinon, from πέτρα, petra, ‘rock’ (whence petroleum, ‘rock oil’, and Peter and petrichor and so on), plus σέλινον, selinon, ‘celery’. To the ancient Greeks, parsley was just another kind of celery, and if you had to be specific, it was the kind that grew on rocks. (The taxonomic Latin name appends crispum, which means not ‘crispy’ but ‘curly’, and I would like to think that I do not need to explain why.)
But petroselinum is a mouth-full, and one seldom wants a whole mouth-full of this plant; although it is, we are informed, packed with vitamin C, when fresh it has a flavour best characterized as aggressive – not just green and pert but, with the volume up, argumentative; when it is dry (as it can be bought in large jars), though its flavour is tamed (meaning murdered), it is… dry. Who wants a mouth-full of dry parsley flakes. My goodness.
So even the later Latin speakers, finding petroselinum articulatorily impertinent, wore it down a bit to petresilium (which Oxford calls “an unexplained alteration” of the original, but you see I have just explained it, and if you try to say petroselinum with your mouth full you, too, may well get to petresilium). The French, whose great linguistic tradition has been to cook Latin down to where it may be easily had with a glass of wine, soon enough made that persil. Meanwhile, the German tongues made Petersilie (which is not to be confused with silly Peter), which transferred unaltered to English until we formed a greater taste for the French. Medieval English cookery-books often called it persil or persel – and they called it often, as it was an herb most regularly used. Here you see it in a recipe from The Forme of Curie for pygges in sawse sawge, which is to say pigs in sage sauce:
Take Pigges yskaldid and quarter hem and seeþ hem in water and salt, take hem and lat hem kele. take persel sawge. and grynde it with brede and zolkes of ayrenn harde ysode. temper it up with vyneger sum what thyk. and, lay the Pygges in a vessell. and the sewe onoward and serue it forth.
Here, allow me:
Take scalded pigs and quarter them and boil them in water and salt, take them and let them cool. Take parsley and sage and grind it with bread and hard-boiled egg yolks. Temper it up with vinegar somewhat thick, and lay the pigs in a vessel, and then so on and serve it forth.
(I would like to write a cookbook in which I could put “and then so on.”)
Older English cookery has no recipes centring on parsley, as a little goeth a long way. But Henry VIII was known to like parsley sauce, which was – and is – a simple white sauce flavoured with parsley. If, however, you head the other way from Greece and cross over the Mediterranean to the Levant, you will find tabbouleh (or any of several other spellings of تبولة tabūla), in which the star ingredient is parsley – which in Arabic is called مَقْدُونِس maqdūnis, meaning ‘Macedonian’ (from an original form calling it Macedonian coriander).
Parsley can also be seen dancing on top of many a dish throughout Europe, where, as everywhere, it packs a pretty punch. In Russia it is called петрушка, petrushka, and in Poland pietruszka, which are homonyms for the puppet character we know as Petrushka, who is sometimes presented as a sad doll but is really the Slavic version of Punch (as in and Judy). The homonymy is a coincidence, we are assured; it is just because of that Greek Peter connection. In Hungary, our plant is petrezselyem and is often the only green thing in sight as it floats in your paprikás; in Sweden, persilja may flavour the potatoes on your smörgåsbord. You can also have your prezzemolo in copious amounts in Italy as part of salsa verd eand gremolata, and if you come over to Brazil you will get your fill of perrexil in cheiro-verde. And in France, you cannot season a good sauce without a bouquet-garni, and you cannot make a decent bouquet-garni without parsley.
In the United States and Canada, however, for a long time, parsley was hidden in sauces or presented on plates as a garnish. Although those who prefer to cook with it generally prefer the flat-leaf kind, the curly kind is especially popular for ornament, and I can say, as someone who has always eaten the parsley that comes on my plate (even as a child treated to what passed for decent dining in 1970s Alberta), that the flavour may take your tongue to the mat, but the spiky little curls will nail it down.
I must be fair: the American orbit is not the only place parsley is seen as prettification. Although (as noted) Italian cuisine makes good use of the flavour of prezzemolo, there is a diminutive form, prezzemolina, that is sometimes used to refer to pretty women serving ornamental functions (as on some television shows). I do not endorse this, naturally, but it is apposite in that parsley is much stronger and has much better taste than many of the things it is used to ornament, and those who refuse to take it seriously are probably going to live an unnecessarily insipid life and drop dead all the sooner from their insalubrious habits.