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Dioecious tree, 5–12 m in height, trunk up to 65 cm diameter, with brownish fissured bark. Branchlets stout, quadrangular and tomentose. Leaves with petiole 1–2 cm, blade lanceolate or elliptic oblong 7–20 × 2–6 cm, subcoriaceous, upper surface glabruos, densely tomentose beneath; apex acute to acuminate, base obtuse or acute, leaf-margins entire. Inflorescence 6–20 × 8–10 cm, occasionally with two orders of branches, comprising globose heads of 40–50 flowers in racemes, 1.2–2 cm in diameter. Calyx tubular, exterior densely stellate-tomentose, 1.5–2.5 mm long. Corolla orange, darker inside than outside, tubular-funnelform, tube 4–5 mm with a few warty hairs in upper part in the interior, lobes orbicular, 2–2.5 × 2.5–3 mm, tomentulose on exterior of lobes. Stamens subsessile, inserted 1 mm below mouth, anthers 0.7–1 mm long. Ovary tomentulose, 1.5 × 2 mm, stigma clavate, 1 mm long. Capsule narrowly ellipsoid, tomentulose to glabrescent. Seeds 1.5–2 × 0.35–0.45 mm, fusiform, prominently winged. (Norman 2000).
Distribution Guatemala Mt. Tacana Mexico Chiapas
Habitat Open areas associated with evergreen cloud forest, at altitude 2700–4000 m.
USDA Hardiness Zone 8b-9
RHS Hardiness Rating H3
Conservation status Not evaluated (NE)
A species with a restricted range, Buddleja megalocephala is found only in the highlands of Guatamala and Mt. Tacana on the Mexico-Guatamala border. Individual plants may be either pistillate (female) or staminate (male). Superficially, the burnt-orange globose flowers resemble B.globosa, to which it is only distantly related, actually being a member of the Cordatae series of Neotopical species. B. megalocephala can grow into a substantial tree in its native habitat, second only in size to the more closely-related B. cordata (Norman 2000).
It has only recently been introduced into cultivation and thus far has formed only large shrubs in temperate gardens or under cover. B. megalocephala has proven borderline hardy given sufficient shelter; a specimen has survived outside for many years at Batsford Arboretum (Gloucestershire, UK), regularly surviving winter temperatures of c. –5ºC, although it has been shy to flower (pers. obs.). Most specimens in the UK are pot-grown and kept under-cover for at least part of the year, conditions where the species is unlikely to realise its full size-potential. The collection available in the trade, BSWJ 9106, is believed by the current author to be a staminate (male) plant.