The long leaf pine has a grass phase where it just looks like grass

Trees are weird, because there phylogenetically there is no such thing as trees. As in: there is no single branch of the evolutionary tree where trees split off from other plants and there’s just an entire branch of different trees. Instead, different plants in separate parts of the evolutionary tree evolved into trees, and sometimes back into non-tree plants, and sometime even back into trees again. So a tree that spends part of its lifecycle as grass is par for the course.