Leucophyllum is a genus of shrubs from the deserts of the southwestern United States and Mexico. These plants are in the Scrophulariaceae, or figwort, family. They are known as sages, but are unrelated to Salvia species, which are the true sages. These evergreen shrubs are often chosen for their silvery-gray leaves and purple-lavender flowers. The plants are highly drought-tolerant and are used in xeriscaping, or landscaping that minimizes water usage.
The leaves appear silver-colored because of the large number of hairs, or trichomes, on them. The flowers are borne where the leaf connects with the stem. This is known as the axil. The axillary flowers can be found on all surfaces of the plant throughout the summer, and into the autumn.
Leucophyllum has the ability to burst into bloom before it rains. This is because these types of plants are highly sensitive to the degree of humidity in the air. For this reason, they are sometimes called barometer plants.
Many of the species are cultivated. The plants require full sun and do poorly in the shade. Once established, they generally do not require maintenance, if grown in areas in which they are native.
This genus grows in alkaline soil, including desert soil that has cement-like caliche. The plants are also tolerant of salt. They can survive in acidic soils, if one adds dolomitic limestone to the soil. These desert sages should be planted in a raised bed, if they are being grown in soil with poor drainage or in an area that receives a lot of rain.
One species in particular that is commonly grown is Leucophyllum frutescens. This shrub has several common names, among them Texas ranger, Texas sage, and cenizo. Due to the hardiness of this plant, it is frequently grown in medians and by highways.
Texas ranger can grow to be 8 feet (2.4 m) tall and equally wide. Shorter cultivars are available for home gardens, however. This shrub will grow in the desert heat, yet is hardy down to 5°F (-15°C).
There is a tendency to shear the plants into rounded balls to make them look like a typical hedge. This is not healthy for the shrubs and will reduce the amount of flowers produced. If necessary, one should selectively prune branches and leave the natural shape. Ideally, Leucophyllum species should not be pruned at all. With dwarf cultivars available, shrubs of the appropriate size can be chosen for home gardens.
In areas with summer monsoons, such as Arizona, Texas ranger does not require any supplemental watering. In very dry areas, it should be watered infrequently but thoroughly. Over-watering and poor drainage are the factors most likely to result in the death of Leucophyllum plants.