Likely a shift in spelling from synonymous and homophonous 棉花 (menka), from Middle Chinese 棉花 (MC miᴇn hˠua, literally “cotton + flower”).
綿花 (hiragana めんか, rōmaji menka, historical hiragana めんくわ)
- raw cotton, cotton on the bush, a cotton flower
Compound of 綿 (wata, “cotton”) + 花 (hana, “flower”). The hana changes to bana as an instance of rendaku (連濁).
綿花 (hiragana わたばな, rōmaji watabana)
- (archaic) an artificial flower made of cotton
- Traditionally worn by male dancers as a kind of 挿頭 (kazashi, “traditional decorative hairpin”) for the 男踏歌 (otoko tōka) dance, held on the 15th day after the Lunar New Year in ancient Japan until the late Heian period.