reed, rush
蘆 centers on tall, water-loving grassy plants: reeds and rushes. The two meanings are essentially the same kind of plant.
蘆 combines the grass radical 艹 with 盧, which likely provides the sound. The character refers to reeds or rushes, plants associated with grassy wetlands.
The top 艹 is grass, and the bottom 盧 looks like a dense cluster of stalks with roots and leaves. Picture a thick patch of reeds growing by the water.
For ロ, imagine a row of reeds lining a riverbank: row -> ロ, and the reeds stand in a long row.