Not all plants found in the desert regions are seed bearing. One of my personal favorites, this species belongs to Lycopodiophyta, which is considered the oldest of the extant plant lineages, having descended from a division in the plant family that occurred around 410 million years ago. Found in the mountainous regions at the base of rocks and outcroppings, they are easily missed and generally ignored.
Despite its moss like appearance and name, S. watsonii is a true vascular plant, and has leaves, roots, and stems. Unlike seed plants, this species reproduces by spores. Like all members of its lineage, the leaves are an independently evolved structure from those of either the lignophyte (seed plant) or pteridophyte (fern) line. In essence, they're much like the wings of a bird vs. the wings of a bat. They are a similar structure that performs the same function, but arose separately and independently.
Because of the small size of these plants, and that they perform very little in the ecology they occupy, this species, as well as other members of its lineage, get only minor attention in the scientific community. While this is understandable, it also does them injustice, as they represents something that has persisted since before mammals, or even reptiles, entered the scene.