Mathrengyl Bearwalker is a level 60 druid trainer located in the Cenarion Enclave in the night elf city of Darnassus. He also sells Packets of Tharlendris Seeds and Evergreen Pouches once the character in question has finished the quest [50] Morrowgrain Research (Alliance, 2).
He starts the following quests:
[10] Moonglade
[10] Body and Heart
[14] Lessons Anew
[16] A Lesson to Learn
[50] Morrowgrain Research (2)
[55] Morrowgrain to Darnassus (Repeatable)
[55] Rabine Saturna (Alliance)