Astralaria IV, Star Chart: Gnarl of Melandru
https://wiki.guildwars2.com/wiki/Star_Chart:_Gnarl_of_Melandru
It looks like it is the rock just before the string of mushrooms on the path up to the Cluster of Light. You will be past the chest.
The Hidden Garden walkthrough for that portion says:
“Cluster of Light
Obtained from the Cluster of Light in the Hidden Garden. The cluster is located on the very top of the tree in the center of the garden. To start up the tree, go up from the south east side. Make your way up to the chest, which is about 1/3 of the way up the tree. Head to the chest, then turn left. There will be a path of mushrooms and roots that you can climb up. (this is probably where the rock is) Be warned, if you fall once you start climbing mushrooms you will die unless you can land in the small pond below.”
Hope this helps.
Yes, you have to climb up a bit to the spot where the cantle of the sun is. Stand on the rock before the LAST string of mushrooms that leads up to the cantle, and then use the cartographer’s gear. I don’t understand why the instructions are so vague on some of the star chart locations either.