Why does 首饰的饰 have the 饣radical?
TL;DR : 饣 is the phonetic, not the signific.
饣, which is simplified from 食, is the radical of 饰/飾 only in the sense that it is listed that way in a Chinese dictionary. It is not the meaning-bearing part of the character. Here are two possible analyses. In both cases, 饣 is contributing to the pronunciation, not the meaning:


飾 = 食 (phonetic: shi2) + 布 (signific: cloth)

飾 = 飤 (phonetic: si4) + 巾 (signific: cloth)

飾 = 食 (phonetic: shi2) + [人 + 巾] (signific: person + cloth)




The first analysis might seem the most plausible, given the character's present appearance, but if you look at the seal script forms for 飾 and for 布, you'll see that the right side of 飾 doesn't really look much like 布.

The second analysis has the appeal that it's a simple phonetic + signific, but @Claw points out that both 飾 and 食 are checked-syllables in Cantonese, while 飤 is not. This indicates that 食 is a much better phonetic match to 飾.

As alluded to in 1, the right side (in seal script) doesn't look like 布, it looks like 巾 underneath a 人-like fragment. As pointed out by another answerer, cloth+person is a good signific for &quot;decorate&quot;.


Edit: Added analysis #3, which Claw suggests is the most plausible, incorporating his arguments.