Leucophyllum is a genus of roughly a dozen species of evergreen shrubs in the figwort family Scrophulariaceae (sometimes alternatively placed in Myoporaceae), native to the arid and semi-arid landscapes of the southwestern United States and Mexico. The genus is colloquially known as barometer bush, barometerbush, or "sage" — though it bears no relation to the true sages of the genus Salvia.
Plants in this genus are characterized by dense trichome-covered foliage that gives the leaves a pale, almost silvery-white appearance — a trait encoded in the genus name itself (from the Greek λευκός, "white," and φυλλον, "leaf"). The flowers are solitary, borne in the leaf axils, and are bell- or funnel-shaped with five lobes arranged into two lips; flower color ranges from white through pink and magenta to purple depending on the species.
Leucophyllum shrubs are adapted to sandy soils and tolerate high salt concentrations. They are notable among gardeners and landscapers for their role in xeriscaping: they require minimal supplemental irrigation, can be easily shaped into formal hedges, and produce bloom over their entire surface rather than at branch tips. Many cultivars have been selected from species including L. frutescens, L. candidum, L. laevigatum, L. langmaniae, L. pruinosum, L. revolutum, and L. zygophyllum.
One of the genus's most distinctive traits is its apparent ability to "forecast" rain. The shrubs typically bloom several days before a rainstorm, apparently responding to rising ambient humidity rather than actual precipitation. This behavior, believed to be a survival adaptation in the plants' semi-desert habitats, is the origin of the common name "barometer bush."
Etymology
The genus name Leucophyllum is derived from the Greek words λευκός (leukos, meaning "white") and φυλλον (phyllos, meaning "leaf"), a direct reference to the pale, whitish foliage produced by a dense covering of trichomes on the leaves.
Distribution
Leucophyllum is native to the southwestern United States and northern Mexico, where species grow in sandy, often saline soils across semi-arid and desert scrub habitats. GBIF records 19 accepted descendants in this range.
Ecology
The genus is strongly adapted to xeric conditions, tolerating sandy soils, high salinity, and low rainfall. Leucophyllum shrubs are famous for blooming several days before rainfall events, apparently triggered by elevated humidity rather than actual precipitation — a trait thought to be an adaptive response to unpredictable rainfall in their semi-desert habitats, earning the colloquial name "barometer bush."
Cultivation
Several species and numerous cultivars are widely used in xeriscaping and ornamental landscaping across warm, arid regions. Leucophyllum shrubs require minimal irrigation once established, are easily pruned into formal hedges, and bloom prolifically across their entire canopy. Cultivars have been developed from L. frutescens, L. candidum, L. laevigatum, L. langmaniae, L. pruinosum, L. revolutum, and L. zygophyllum.
