avena nuda
莜 refers specifically to a type of wild oat, Avena nuda, a grain plant. Its meaning is narrow and botanical, with no clear broader conceptual center beyond this plant.
莜 combines the grass radical 艹 with 攸, which likely contributes sound. The character is a specific plant name, and its historical development is not widely documented.
The grass radical 艹 sits above 攸, like a wild oat plant growing tall. Picture a field of Avena nuda with its distinctive seed heads.
For テキ, imagine using a technique to harvest the wild oats: technique -> テキ, and the grass 莜 is gathered with skill.