Contributers to a well balanced subtropical garden are "palm like plants" such as cycads, tree ferns, Cordylines, Beaucarnias, and Yucca.  These plants are often confused with palms as they have a similar look.  Cycads in particular look very palm like but are a completely different family of plants, in fact one that is very much more prehistoric than palms, existing at the time of the dinosaurs long before palms evolved.  Instead of bearing seeds like palms, they bear cones and thus are "coniferous" more related to pine trees than palms.  But don't tell them that, they seem perfectly natural and content hanging with all their palm pals.  

 

The fern family is also an anchient one pre dating the emergence of palms on our planet.  They can exist as tiny little plants inhabiting the cracks in rocks and become treelike growing to 25' tall.  Tree ferns look similar to palms with a central stem and radiating fronds much in the shape of a typical palm and can add a strong dose of lushness to a garden.

 

Various Cordylines all originating from the Western Pacific region can very from large and treelike such as Cordyline australis to the more miniture Cordyline stricta.  Many colorful hybrids have been developed over the years that now offer an all year rainbow of foliage coloration.  Yuccas and Beaucarnias will impart a more xeric and sometimes southwestern flair to the garden working well with cactus, agaves and other succulants.