In Greek mythology, Alseids (/ælˈsiːɪdz/; Ancient Greek: Ἀλσηΐδες, romanized: Alsēḯdes) were the nymphs of glens and groves. Of the Classical writers, the first and perhaps only poet to reference alseids is Homer. Rather than alseid he used the spelling alsea. The three uses of alsea by Homer are as follows:

"The nymphs who live in the lovely groves (ἄλσεα, álsea), and the springs of rivers (πηγαὶ ποταμῶν, pēgaì potamôn) and the grassy meadows (πίσεα ποιήεντα, písea poiḗenta)."^[1]

"They [nymphs] come from springs (krênai), they come from groves (alsea), they come from the sacred rivers (ποταμοί, potamoí) flowing seawards."^[2]

"The nymphs [of Mount Ida] who haunt the pleasant woods (alsea), or of those who inhabit this lovely mountain (ὄρος, óros) and the springs of rivers (pegai potamon) and grassy meads (pisea)."^[3]