Glandora is a small genus of low-growing, evergreen shrubs and subshrubs in the borage family (Boraginaceae), order Boraginales. Native to the western and central Mediterranean region, its range spans Morocco, Algeria, Portugal, Spain, France, Italy, and Greece, where species typically grow in rocky, well-drained habitats.
The genus was segregated from Lithodora in 2008. Both genera share a characteristic growth form: dense, mat-forming or spreading subshrubs with narrow, dark green, hairy leaves and clusters of tubular, five-lobed flowers. Flowers are most commonly a vivid azure blue, though white-flowered forms occur in some species. The blue of Glandora blooms is among the most intense produced by any temperate garden plant.
The most widely cultivated species, Glandora diffusa (formerly Lithodora diffusa, common name purple gromwell), grows to about 15 cm tall and spreads to 60 cm or more, making it a popular choice for rock gardens and alpine plantings. Several cultivars with especially deep blue flowers have been selected for garden use.
The genus contains around eight to ten accepted species, including G. rosmarinifolia, G. prostrata, G. nitida, G. moroccana, and G. oleifolia, all restricted to western Mediterranean Europe and North Africa.
Etymology
The name Glandora is derived from the genus Lithodora, from which it was split; lithodora in ancient Greek means "stone gift" (lithos, stone + doron, gift), a reference to the preferred rocky, stony habitats of plants in this group. The species epithet diffusa (spreading) and the common name "purple gromwell" reflect the growth habit and flower color of the most familiar member.
Distribution
Glandora is native to the western and central Mediterranean basin, occurring in Morocco, Algeria, Portugal, Spain, France, Italy, and Greece. Species grow primarily in rocky, sunny terrain including limestone outcrops, garrigue, and montane habitats.
Ecology
Species of Glandora favor open, rocky, well-drained sites in full sun. Glandora diffusa is documented as requiring acid to neutral, well-drained soil and being susceptible to root rot in poorly drained conditions; it also requires vernalization (winter cold) to flower. The genus name's root — "stone gift" — reflects this association with rocky, stony ground.
Cultivation
Glandora species, particularly G. diffusa, are grown as ornamental plants in rock gardens, alpine gardens, and raised beds, valued for their intense azure-blue flowers. Glandora diffusa is hardy to approximately −23 °C (USDA zones 6–8) and requires a sunny position with acid or neutral, well-drained soil. Numerous cultivars of G. diffusa with especially vivid blue flowers have been selected for horticulture.
Taxonomy Notes
Glandora was separated from Lithodora in 2008. The two genera are closely related within Boraginaceae and share similar morphology; the split is based on molecular and morphological distinctions. Lithodora now comprises three species confined to southwestern Europe, southern Greece, Turkey, and Algeria, while Glandora holds the western and central Mediterranean species formerly treated under Lithodora.
