As a birder, I always thought hybrids were straight forward like Mallard X Northern Pintail would be (Anas platyrhynchos x acuta) with the scientific name having the genus plus the two species it’s mixed with, with a “x” between the two species. Yet with plants it’s totally different.
For example, the Beach Strawberry (Fragaria chiloensis) and the Virginia Strawberry (Fragaria virginiana) hybridize and create the Garden Strawberry (Fragaria x ananassa). I don’t see how that makes sense. I heard the “x” indicates it’s a hybrid but how does changing the species/hybrid scientific name help people know the plant’s parents. What’s the reasoning behind it?
you might also notice it where the parents have undergone taxonomic revision and are found to be synonyms of earlier names, so the older name replaces it. However, for the (assumed stable and naturally occuring) hybrids, the first name given stands as the earliest used.
Article H2 allows a hybrid formula to be used (ex: Agrostis stolonifera × Polypogon monspeliensis)
Article H3 allows a hybrid to be named separately, as in your Fragaria × ananassa example.
Note: named plant hybrids are sometimes referred to as nothotaxa (nothospecies, nothogenus, etc.)
By clicking on the left or right arrows on the web pages for the above articles, one can really geek out and scroll through all 12 articles governing the naming of plant hybrids.
Note that the above applies to naturally occurring hybrids named within the general framework used by plant taxonomists. There is a whole separate International Code of Nomenclature for Cultivated Plants used for hybrids and other cultivars created artificially in cultivation by horticulturists.
One thing that happens with plants and not so much animals, is that plants like to hybridise. All the time. Many, many plant genera have many viable natural hybrids between two or more species, and some families, such as the orchids, have a profusion of hybrids even between different genera. In animals, hybrids are a rare occurrence, normally sterile, and historically they have usually been recognised as such. Hybridisation followed by polyploidisation is even recognised as a viable and possibly common method of speciation in plants (allopolyploidy).
In plants, where many of these hybrids are perfectly viable, they have often been described as separate species, long before someone realised that they were a hybrid. For example, the hybrid between Ozothamnus ledifolius DC. and Ozothamnus hookeri (Sond.) Druce was originally described as a variety of the latter: Helichrysum hookeri var. expansifolium Sieber ex P.Morris & J.H.Willis. This was later upgraded to full species as Helichrysum expansifolium (Sieber ex P.Morris & J.H.Willis) N.T.Burb., moved to a different genus as Ozothamnus expansifolius (P.Morris & J.H.Willis) Anderb., before someone realised it was a hybrid, so we now insert a multiplication symbol and call it Ozothamnus × expansifolius.
In many cases the plants is known for certain to be a hybrid but the parentage is unknown, or only one parent is known. As @jdmore points out above, both forms are acceptable for referring to hybrids: using their validly described name with a multiplication symbol to indicate a hybrid, or with the formula Genus speciesA × G. speciesB. Using the example I gave above, it would be Ozothamnus hookeri × O. ledifolius. However, in cases where the parentage is uncertain or unknown, only the Ozothamnus × expansifolius form makes sense.
If this subject interests you, I heartily recommend you read “The Naming of the Shrew: A Curious History of Latin Names” by John Wright. It covers this question and a thousand similar aspects of taxonomy in a really entertaining and readable way. In the first chapters, I was slightly disappointed that it was mostly amusing trivia about silly and strange scientific names, but it quickly moved on to some fascinating discussion of all the conventions around naming, the history of how it came about, the differences between zoology and botany, etc. I really highly recommend it!
Side Note: Strawberries are weird in the chromosome department, being polyploid. Having varying multiple of 7s depending upon species, not a set number. From a quick reading of material, apparently not that weird in hybrids. This apparently is one reason why a lot of plant hybrids are fertile.