sedge (archaic term)
Archaic word for a type of sedge (a grass-like plant). The cross-reference to 菅 (すげ) suggests it may be an old variant or specific kind of sedge. Not used in modern Japanese outside of historical or literary contexts.
See also: スゲ
The word 真菅 can sometimes be found in old waka poems.
The exact derivation is uncertain. The kanji 真 (ま) often serves as a prefix meaning 'true' or 'genuine', and 菅 (すげ) means 'sedge'. The reading ますげ may be an old compound or a specific plant name.