Ah, that wasn't entirely clear to me, this makes more sense. Palm trees do "grow from a central stem that is nearly perfectly vertical", and are woody, and con

Ah, that wasn't entirely clear to me, this makes more sense. Palm trees do "grow from a central stem that is nearly perfectly vertical", and are woody, and conventionally are considered trees. Bamboo matches both of those criteria, in fact, but it has a "just look at it" grassness to it. Growing in clusters from rhizomes is pretty un-tree-like, but no one of these things is diagnostic. What is and isn't a tree is more cultural than biological, which is, I believe, the original author's point.