wild vine, vitis pentaphylla
蘞 refers to a specific wild vine, vitis pentaphylla. Its meaning is narrow and botanical, without a broader conceptual center.
蘞 combines the plant radical 艹 with 斂, which likely contributes the sound. The exact historical development is uncertain.
The grass top 艹 signals a plant, and the complex bottom 斂 suggests a tangled, wild vine.
For レン, imagine a wild vine wrapping around a lens: lens -> レン, and the vine's tendrils curl around the glass.