Lithodora diffusa

Lithodora diffusa, the purple gromwell, syn. Lithospermum diffusa, is a species of flowering plant in the family Boraginaceae. It is a mat-forming perennial growing to 15 cm (6 in) tall by 60 cm (24 in) or more wide, with dark green, hairy evergreen leaves and masses of blue or white 5-lobed flowers. It is suitable for cultivation in a rock garden or alpine garden.[1]

Lithodora diffusa
L. diffusa, Osaka Prefectural Flower Garden, Japan
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Boraginales
Family: Boraginaceae
Genus: Lithodora
Species:
L. diffusa
Binomial name
Lithodora diffusa

Although there is a variety with white flowers, L. diffusa var. alba,[2] the blue-flowered varieties are most valued in gardens for the intense azure color of their abundant blooms. Numerous cultivars have been developed for garden use, of which 'Grace Ward'[3] and 'Heavenly Blue'[4] have gained the Royal Horticultural Society's Award of Garden Merit.[5]

Lithodora diffusa is hardy down to −15 °C (5 °F) (USDA zones 6 - 8),[2] and requires a position in full sun. It needs a well-drained acid or neutral soil, as it is susceptible to root rot. It requires vernalization to flower.[6]

The ancient Greek term lithodora literally means "stone gift", referring to its preferred habitat. Diffusa means "spreading", and refers to the plant's growth habit.[7]

References
  1. RHS A-Z encyclopedia of garden plants. United Kingdom: Dorling Kindersley. 2008. p. 1136. ISBN 1405332964.
  2. Armitage, Allan (1989). Herbaceous Perennial Plants. Athens, GA: Varsity Press, Inc. pp. 385–386. ISBN 9780942375015.
  3. "RHS Plant Selector - Lithodora diffusa 'Grace Ward'". Retrieved 23 February 2020.
  4. "RHS Plant Selector - Lithodora diffusa 'Heavenly Blue'". Retrieved 23 February 2020.
  5. "AGM Plants - Ornamental" (PDF). Royal Horticultural Society. July 2017. p. 61. Retrieved 25 March 2018.
  6. "Lithodora diffusa 'White Star' Technical Guide" (PDF). Blooms of Bressingham. Retrieved 2017-01-07.
  7. Coombes, Allen J. (2012). The A to Z of plant names. USA: Timber Press. pp. 312. ISBN 9781604691962.
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