Matopomo
Knobweed was a fairly common[1] reed that grew outside the Alethi warcamps near the Shattered Plains on Roshar[2] and likely other locations.
Appearance
Knobweed grew on plains of rock in the leeward side of boulders.[1] The stalk of the reed was immobile, attached to the rock. The top of the reed contained a frond that would retract during highstorms. During each storm, some would get pulled free and blown to a new location, where they would reestablish themselves and spread. Knobweed also gives off fluff,[3] for some unknown purpose, possibly reproduction. Of late, knobweeds have become harder to find around the Shattered Plains,[4] possibly due to over-harvesting.
Uses
Knobweed stems are sturdy, they have the potential to be woven into hats.[1]
The sap or "milk" of knobweed is a powerful antiseptic.[1] It is a creamy white color.[4] The sap can be removed from the stalk by squeezing it along the stem.[1] Usually two or three drops are produced. It can be used to clean wounds, or to sanitize hands during surgery.[5]
The trade of knobweed sap is a lucrative business among the apothecaries supplying the warcamps.[4] The highprinces are unaware that the reeds they see growing are knobweed, so the apothecaries charge a high rate, two skymarks. When Kaladin discovered this, he began selling some of the sap he collected for his bridgemen to one of the apothecaries for money to feed the wounded and to pay for the nightly stew's ingredients. The apothecary agreed, even though he received less profit, because he could claim ignorance as to where the reeds were coming from if the Alethi found out what he and the other apothecaries had been doing.