That a little uncertainty attaches to two or three of the Shaksperean botanical names has already been mentioned. One of them, "crow-flowers," occurs in the imperishable Hamlet scene above cited in connection with Ophelia and the willow-.Gerard gives crow-flowers as the equivalent of Lychnis Floscuculi, and upon his authority the latter is very generally accepted.  -Leo H. Grindon, The Shakespere Flora, Simkin, Marshall, London, 1883. p.126f.

These are not used either in medicine or in nourishmeht: but they serve for garlands & crownes, and to decke up gardens. - John Gerard, The Herbal or General History of Plants, 1633 Edition, New York, Dover Pub.,1975. p1259f.

The common title is suggestive of the robin-redbreast, the rosy-red petals, which are ragged in appearance being responsible for the common name Ragged Robin.  -F.G. Savage, The Flora & Folk Lore of Shakespeare, London, Burrow, 1923, p.18