young bamboo
筤 centers on young bamboo: a bamboo shoot or a bamboo that is still tender and not fully grown.
筤 combines 竹 (bamboo) with 良, which likely contributes the sound. The character is used specifically for young bamboo.
The top 竹 is bamboo, and the bottom 良 looks like a tender shoot with a small dot on top. Picture a young bamboo shoot pushing up through the soil.
For ロウ, imagine a row of young bamboo shoots lined up in a nursery: row -> ロウ, and each shoot is a young bamboo.