I believe the term you all are looking for is "Mexican Tree Sydrome"
That is what the extension forester coined it.
Anyways I have heard multiple theories on the Palm Trees.
"They were planted after the great depression as environmental projects for jobs"
"They are part of "Valley" concept of mimicking California's "Valley" culture and tropical feel"
"Some have even said they are all imported and do not belong here"
The facts and reason these trees are important is because we posses one of the most (if not the most) northern stands of palm trees in their native habitat. If you have never been to the Palm Sanctuary in Brownsville it is awesome.




"Even with a river and a wall, Palm trees are native to the LRGV(D) and know no borders"
Essentially they make us cool.