Mertensia is a genus of perennial herbaceous flowering plants in the borage family (Boraginaceae), encompassing approximately 52 accepted species. The plants are best known by their common name "bluebells," though the flowers are typically trumpet-shaped (salverform) rather than true bell-shaped. A distinctive characteristic of the genus is that flowers open from pink-tinged buds and gradually shift to blue — a color change driven by pH variation in the flower tissue, a trait shared across much of the Boraginaceae family.
Plants are leafy perennials bearing flowers arranged in modified, bractless cymes that terminate stems and branches. The corollas range from tubular to funnelform or campanulate, with a clear distinction between tube and limb. Flower color spans blue, pink, and white across the genus.
The genus was established by German botanist Albrecht Wilhelm Roth in 1797 and named in honour of Franz Carl Mertens, a German botanist. Mertensia belongs to tribe Cynoglosseae within subfamily Boraginoideae, and its closest relative is the monotypic Eurasian genus Asperugo.
Diversity is centered in the Rocky Mountains of North America, with a secondary range stretching across extratropical Asia from western China to northeastern Russia. Most species are endemic to small Rocky Mountain areas and inhabit alpine, subalpine, and montane environments. The most widely cultivated species, Mertensia virginica (Virginia bluebells), produces the largest flowers in the genus and has become sparingly naturalized in Europe.
Etymology
The genus name Mertensia honours Franz Carl Mertens (1764–1831), a German botanist. The genus was formally described and named by Albrecht Wilhelm Roth in 1797, published in Catalogus Botanicus (Catal. Bot. 1: 34). Several earlier genus names were subsequently placed in synonymy, including Pneumaria Hill (1764), Casselia Dumort. (1822), Hippoglossum (Rchb.) Hartm. (1832), Platynema Schrad. (1835), Steenhammera Rchb. (1831), and Winkleria Rchb. (1841).
Distribution
Mertensia is native to most of North America and to extratropical Asia, ranging from western China eastward to northeastern Russia. Within North America the genus is most diverse in the Rocky Mountains, where the majority of species are narrowly endemic to small mountain areas. Mertensia virginica is the broadest-ranging North American species, occurring from the Appalachian Mountains westward to Minnesota, Iowa, and Missouri. Mertensia maritima occupies a contrasting niche as an Arctic and subarctic coastal species, growing on shingle beaches around both hemispheres. Herbarium-based counts suggest 35–40 North American and Eurasian species; the Plants of the World Online checklist recognizes 52 accepted species.
Ecology
Most Mertensia species are adapted to alpine, subalpine, and montane environments, reflecting the genus's center of diversity in the Rocky Mountains. Mertensia maritima is an ecological outlier, colonizing nutrient-poor sandy or gravelly shingle by the sea; it is uncommon and declining across its range. Flowers open pink and shift to blue through anthesis, a pH-driven pigment change common throughout the borage family.
Cultivation
Mertensia virginica (Virginia bluebells) is the most widely grown species and has become sparingly naturalized in Europe; approximately 12 additional species are known in cultivation. Mertensia maritima (oysterplant) requires nutritionally poor, very well-drained sandy or gravelly soil in full sun and is hardy in USDA zones 3–7; it resents root disturbance, is highly susceptible to slug damage, and is not considered easy to cultivate.
Cultural Uses
Mertensia maritima, known as oysterplant, has a history of food use in Arctic regions. The roots were traditionally eaten by the Inuit of Alaska. The leaves can be consumed raw or cooked and are described as having a mild oyster-like flavor, though the texture is thick and mucilaginous. The flowers are also edible raw.
Taxonomy
Mertensia belongs to tribe Cynoglosseae within subfamily Boraginoideae of the family Boraginaceae. Its closest relative is the monotypic Eurasian genus Asperugo. The genus is divided into two sections: Stenhammaria (circumboreal and Asian species) and Mertensia (North American species). Approximately 150 species names have been published historically, but many recognized species are polyphyletic; no comprehensive revision has been completed since 1953. A 2014 molecular phylogenetic study recommended recognizing at least 62 species, while the current Plants of the World Online checklist accepts 52. North American species fall into three informal clades: the Pacific Northwest, Southern Rocky Mountain, and Central Rocky Mountain clades.
Propagation
For Mertensia maritima, propagation by seed is possible: sow when ripe in a cold frame and germination typically occurs within one month. Division is the alternative method, performed in April or early September with careful handling to minimize root disturbance.
