Hippuris vulgaris

From LSJ

καὶ νῦν περὶ ἀρετῆς ὃ ἔστιν ἐγὼ μὲν οὐκ οἶδα, σὺ μέντοι ἴσως πρότερον μὲν ᾔδησθα πρὶν ἐμοῦ ἅψασθαι, νῦν μέντοι ὅμοιος εἶ οὐκ εἰδότι → so now I do not know what virtue is; perhaps you knew before you contacted me, but now you are certainly like one who does not know

Source

Wikipedia EN

Hippuris vulgaris

Hippuris vulgaris (from Greek: ἵππος – horse and οὐρά – tail), known as mare's-tail or common mare's-tail, is a common aquatic plant of Eurasia and North America ranging from Greenland to the Tibetan Plateau to Arizona. It prefers non-acidic waters.