You can call these flowers daffodils or narcissus, but none of them is a jonquil. Source: www.jparkers.co.uk http://www.dutchbulbs.com
Confusion reigns in the naming of one popular spring bulb. Should be we calling this plant a daffodil, a jonquil or a narcissus?
First, let’s get the term “jonquil” out of the way.
Although many gardeners think that any yellow daffodil is a jonquil, this term should actually refer only to one of the some 60 accepted species of Narcissus, Narcissus jonquilla, and also to its hybrids (Division VII in the Daffodil Checklist). It produces small white or yellow flowers with a tiny cup, several per stem, but most strikingly, its very upright leaves are tubular, like chives leaves, and not flattened, like those of most other narcissus. This comes from the Spanish origin of the name, as “junquillo” (jonquil) means “little rush”, referring to the rush-like—that is, tubular—leaves. And rush is “junco” in Spanish.
The true jonquil tends not to be terribly hardy and is often mostly seen in Southern gardens, where on the contrary is it very long-lived. Even it‘s best known hybrid, ‘Baby Moon’, is really not that widely grown.
Narcissus (the plural of which can be either narcissus or narcissi, depending on your mood) is, of course, based on the botanical name of the genus and is therefore always correct. It is famously named for the Greek youth Narcissus who fell in love with his own reflection. (You can read How the Narcissus Got Its Name for further information that subject.) You can call any Narcissus by the name narcissus and you’ll always be right. In scientific situations (say, you’re talking to a botanist), it would be the most appropriate one.
As for daffodil, it’s the common name in English-speaking countries for Narcissus plants and flowers. You can use it as you wish: it applies to just about any plant in the genus. One exception I can think of is the “Paperwhite” (Narcissus papyraceus, formerly N. tazetta ‘Paperwhite’), and its relatives. The latter is pretty much always called a Paperwhite narcissus, never a Paperwhite daffodil.
The curious name daffodil is derived from asphodel (Asphodelus spp.), a herbaceous perennial with white flowers that does have certain similarities with white-flowered narcissus like the poet’s narcissus (Narcissus poeticus). No one knows, however, how the “d” got added to the name, making it daffodil.
So, to resume, avoid using “jonquil” unless you’re absolutely sure you’re referring to a true jonquil (N. jonquilla), but you can use daffodil or narcissus pretty much as you choose!