Boreal Starwort

Plants infected with an anther smut, Microbotyrum stellariae (Sowerby) G. Deml & Oberwinkler [Ustilago violacea (Persoon) Roussel, in the broad sense], exhibit flowers with enlarged, reddish anthers. This condition is known in both subspecies, especially in northern areas of the range, but is as yet unknown in Stellaria calycantha, a species previously united with S. borealis by some authors.

Plants perennial, often matted, rhizomatous. Stems prostrate to ascending or erect, usually diffusely branched, sharply 4-angled, (5-)25-50 cm, glabrous to finely papillate, rarely pubescent. Leaves sessile; blade linear-lanceolate to ovate-lanceolate, rarely elliptic-lanceolate, 1-6 cm × 2-8 mm, base cuneate, margins eciliate or scabrid, sometimes ciliate towards base, apex acute. Inflorescences with flowers solitary, terminal and axillary, or terminal, often copious, very lax, leafy cymes; bracts foliaceous, lanceolate, reduced distally to ca. 2 mm, ± scarious. Pedicels erect or patent, usually reflexed at maturity, 10-40 mm, glabrous. Flowers 3-5 mm; sepals 5, 1-3-veined, lanceolate to ovate, 2-5 mm, margins scarious, apex acute, glabrous; petals 5, rarely absent, white or translucent, 1-3 mm, usually shorter than sepals; stamens 5; styles 3, erect to spreading, 0.9-2 mm. Capsules greenish brown or straw colored, ovoid, 3-7 mm, more than 1-1.5 times as long as broad, exceeding sepals, apex acute, opening by 3 valves; carpophore very short or absent. Seeds 10-20, brown, obovate, 0.7-0.9 mm on longest axis, smooth or slightly rugose. 2n = 52.

Alsine borealis (Bigelow) Britton

Stellaria borealis is a species of flowering plant in the family Caryophyllaceae known by the common name boreal starwort. It has a circumboreal distribution, occurring throughout northern areas of the Northern Hemisphere. It occurs in many types of moist and wet habitat, including marshes, riverbanks, lakesides, floodplains, talus, ditches, and moist spots in forests and woodlands. It is quite variable in appearance, especially across subspecies. In general, it is a rhizomatous perennial herb forming mats of branching, four-angled stems lined with lance-shaped leaves a few centimeters in length. The inflorescence bears many flowers each with five deeply lobed white petals. Some flowers lack petals and have only the five pointed green sepals.

This plant is sometimes infected with the smut fungus Microbotryum violaceum (Microbotyrum stellariae), which causes its anthers to turn red.