soap that derives from a plant root (see Karttunen and Lockhart)
The Florentine Codex provides an illustration and a textual description of amolli (spelled hamolli in that manuscript). Above ground it has long, narrow reeds. Below ground, it has two types of roots. The smaller ones are used for soap, such as for washing one's hair. The larger roots can make one go bald. It can serve as a remedy; if one eats a leech, one needs to swallow an infusion of amolli. Small fish find amolli too toxic and can die from it.
See an image that represents amolli in the Visual Lexicon of Aztec Hieroglyphs, ed. Stephanie Wood (Eugene, Ore.: Wired Humanities, 2020-present).
maaltiaia, mahamoviaia, yoan moxocoqualiaia, quichioaia xocotamalli; yoan tlatonilli, anoҫo itzcuintli qujmjctiaia qujquaia, yoan tlaoanaia = They bathed with water; they washed [their heads] with amolli soap. And fruit was eaten—they made fruit tamales, and sauces. Or they slew and ate a dog, and they drank wine. (central Mexico, sixteenth century)
Auh no yquac, netzonpaco in tlamanj, motzopaca, mamouja = The captors washed their heads and washed off the sweat with a soap [called amolli]