73. The "Flat Sun" Radical: 曰
These two shapes may look identical, but a closer examination reveals otherwise:
日 (62: sun, day, date; Sunday; Japan)
曰 (to say), a non-Joyo kanji
The latter character is broader, and the cross stroke actually only goes three-fourths of the way across 曰.
These shapes are also separate radicals, at least theoretically:
日 (radical 72: "sun")
曰 (radical 73: "flat sun"), referred to in Japanese as ひらび (meaning 平日, "flat sun") or いわく (the kun-yomi of 曰く)
Kanjigen does indeed list them as different radicals, but Nelson treats radical 73 as a variant of radical 72.
Here's my thinking. Radical 73 is on duty in these Joyo kanji, according to Kanjigen:
書 (142: writing; book)
曲 (261: piece of music, song; curve)
最 (484: most)
更 (1248: furthermore; to renew; change; grow late; brand-new; night watch)
曹 (1520: low-ranking government official; sodium)
替 (1548: exchange; replacement)
曽 (2052: previously; great- (in family lineage))
That is, the 日 or 日-like parts used to be 曰. But those shapes now look exactly like 日, so I feel it only makes sense to classify all seven characters under radical 72.
To find out about that radical, see Radical Note 72.
Photo Credit: Eve Kushner