On that map, you want to go to Knut Brightwood. If you go past the sigils for his dungeon, you will see the amaranth on that ledge.
To get to Knut Brightwood, walk "around" the open area where you see Coven Frostbeaks and Coven Ravenclaws walking. There is a "green arrow" on the map that points to this open area. Then there is an ice path (between two of the buildings) that leads up to Knut's dungeon. On the map, the ice path (and the two buildings near it) are kind of hidden by the pictures and nametags of the Coven Frostbeaks and Coven Ravenclaws.
Hope this helps.
(Note: if "clicking" on that link doesn't work, you might have to do a "copy and paste" to see the info.)