I recently went looking for one of the rarest of Texas’s rare plants in what seemed like an odd place: near the middle of Boerne. At Cibolo Nature Center, a hundred-acre preserve adjacent to Boerne City Park, a serene stretch of Cibolo Creek lined with bald cypresses ran clear and shallow. The bare tree trunks cast sharp shadows, while a carpet of low-level green growth glowed in the sun beyond them.Around a curve and through the woods, David Touchon, the Cibolo Center for Conservation’s land manager, pointed out some gangly gray stems protruding from a tangle of roots on the edge of a mossy embankment. “Sycamore-leaf snowbell,” he said proudly. This subspecies in the Styrax genus is among several rare endemics—plants found nowhere else in…