a plant with an edible root, or the root itself
Clavijero (1780) says this is a medicinal root; it is a personal name in the Matrícula de Huexotzinco; and, the Digital Florentine Codex keywording team translates cimatl as "runner bean;" also called a wild potato, heartleaf horsenettle, or heartleaf nightshade (see attestations)
See an image that represents cimatl in the Visual Lexicon of Aztec Hieroglyphs, ed. Stephanie Wood (Eugene, Ore.: Wired Humanities, 2020-present).
The Florentine Codex, Book 11, f. 128r-v., includes the cimatl (the name of the root), and mentions that the greenery is called cuahueco (quaueco). The cimatl must be cooked in a pot or it is fatal. A variety is the tolcimatl, with chili-red blossoms and cylincrical roots. It is edible raw or cooked in an olla (128v).
"It is commonly known as cimatli (along with S. ehrenbergii), heartleaf horsenettle, or heartleaf nightshade. This is one of the few wild potato species that was commonly used as food. The Aztec and the Chichimeca ate S. cardiophyllum and the practice continues in some parts of Mexico today (Johns 1990). In fact, there was at least one farm that was growing S. cardiophyllum, S. ehrenbergii, and S. stoloniferum for market in Jalisco as recently as 2010 (Villa Vazquez 2010)." The leaves are shaped like hearts.