Dioecious multi-branched shrub, 0.5 to 2 m high, with greyish-black fissured bark. Branchlets terete and tomentose. Leaves shortly petiolate, blades ovate to rhomboid 1.0–6.0 × 0.6–2.5 cm, membranaceous to sub-coriaceous, densely tomentose on both surfaces with underlying glandular trichomes; apex obtuse or rounded, base cuneate, acute or attenuate; margin crenate. Inflorescence terminal globose head 0.8–1.2 cm diameter, comprising of approximately 35 flowers, subtended by a pair of bracts; calyx campanulate, externally tomentulose with glandular hairs 2–3.5mm long; corolla deep yellow turning orange, salverform, outside tomentulose on upper third, tomentose with trichomes at base, inside with scattered warty hairs primarily below the stamens, corolla tube 3–4.5 mm long, lobes orbicular 1–1.5 × 1.5–2.0 mm. Stamens subsessile, inserted in upper third of the corolla tube, anthers 0.6–1.0 mm. Ovary tomentulose with glandular hairs towards upper half, style 1.0–2.0 mm long, stigma clavate, 0.6–1.0 mm long. Capsule oblong-ovoid 3.0–4.0 × 1.5–2.0 mm tomentulose at the apex. Seeds narrowly ellipsoid, winged at one end, 1.0–1.3 × 0.2–0.3 mm. (Norman 2000).
Distribution Mexico Chihuahua, Coauila, Durango, Hidalgo, Nuevo León, San Luis Potosí, Tamaulipas, Zacatecas. United States Texas
Habitat Arid limestone and gypsum soils, in canyons and arroyos (dry gullies), at altitude 600–2250 m asl.
USDA Hardiness Zone 9-10
RHS Hardiness Rating H3
Conservation status Not evaluated (NE)
Buddleja marrubiifolia was described by George Bentham in 1846 and was named for the resemblance of its leaves to common horehound (Marrubium vulgare). This Buddleja species forms a small, scrubby shrub; the foliage is small and elliptical in shape, and is grey-green with a covering of fine hairs. It flowers from spring until summer producing nectar-rich inflorescences the size and shape of a single marble (~1 cm diamater), which turn from pale orange-yellow to a burnt-orange colour as they mature. A dioecious species with individual plants producing either staminate (male) or pistillate (female) flowers.
The species grows in arid montane habitats across several regions of Mexico and also in Texas. Introduced into horticulture relatively recently, it was first in cultivated as an ornamental in Arizona (before 2000), and later was introduced more widely by specialist nurseries in both the US and Europe. It is very tolerant of heat, intense sunlight and drought. However, its adaptation to a xeric environment means it is extremely sensitive to damp and will not grow well in heavy or wet clay soils. B. marrubiifolia requires a very free-draining growing medium and should be watered only sparingly as it is prone to rotting off. Although reasonably tolerant of cold, purportedly down to as low as –10ºC, it is not suitable for growing outside in any region with significant winter rainfall and is probably best grown in a pot undercover where moisture levels can be controlled (Norman 2000, Stuart 2006).
RHS Hardiness Rating: H3
USDA Hardiness Zone: 8a-10b
Buddleja marrubiifolia ‘Presidio’ is a selection made by Logan Calhoun and available via the Plant Delights Nursery, USA. Selected for increased hardiness, it is otherwise identical to the species (Carey & Avent 2010).