L. H. Shinners (1965) dem-onstrated that Holosteum umbellatum has been introduced in North America on several occasions. Collections from northeastern North America are mainly older ones from very localized populations, the first from near Lancaster, Pennsylvania, in 1856. Reports from the central United States show its occurrence there in several states in the 1940s, spreading rapidly along roadsides, railroads, and other calcareous sites. M. L. Fernald (1943f) suggested that H. umbellatum may have been spread as a contaminant in grass seed sown after highway construction in Virginia (see 34.2. Petrorhagia prolifera and 34.4. P. dubia for similar cases). The first collection from the western United States was made in 1926 and the species has since spread to various disturbed sites in the Pacific Northwest. Several plants in two recent collections from Oregon (e.g., Joyal 463, OSC) are infected with an ovary smut (Microbotryum sp.), the first evidence of such infection on Holosteum in North America known to us.
The early appearance and extremely brief life cycle of Holosteum umbellatum probably contribute to its being overlooked. It should be expected elsewhere in our range.
Annual herb with a slender taproot 10 - 30 cm tall Stem: ascending to upright, unbranched, glandular (especially near the middle, but usually smooth above and below), with a somewhat waxy coating (glaucous). Inflorescence: a terminal cluster (umbellate cyme) of three to fifteen flowers subtended by two to four bracts. Bracts scarious-margined (dry, thin, and membranous). Flowers: white to pinkish. Stalk reflexed, slender. Stamens three to five. Styles three. Sepals: five, distinct, white along the margins, about 3 mm long. Petals: five, white to pinkish, clawed, irregularly fringed at the tip. Fruit: a dehiscent, thin-walled capsule (opening by six teeth), more or less cylindrical, on 1.5 - 3 cm long stalks. Seeds numerous, 1 mm long, oblong, shield-shaped, compressed, rough. Basal leaves: in a rosette, often short-stalked, 1 - 2.5 cm long, oblong to reverse lance-shaped, one-veined, glandular around the margins. Stem leaves: few, opposite, stalkless.
Similar species: No information at this time.
Flowering: April to mid-June
Habitat and ecology: Introduced from Eurasia. An infrequent weed of disturbed, sandy areas, including roadsides and cemeteries. It is also found in sandy nursery rows.
Annual, somewhat glaucous; stems tufted, unbranched, 1-3 dm, stipitate-glandular especially near the middle, generally glabrous at top and bottom; lvs stipitate-glandular around the margins, the basal ones tufted, oblong to oblanceolate, 1-2.5 cm, often short-petiolate, the cauline few and sessile; peduncle much surpassing the lvs, with 3-15 fls on slender pedicels that elongate to 1.5-3 cm in fr; sep ca 3 mm at anthesis, somewhat accrescent; pet generally a little longer than the sep; stamens 3-5, alternipetalous; capsule well surpassing the cal, its valves ±strongly outrolled from the tip; seeds 1 mm; 2n=20. A weed of waste places, native to Eurasia, widely intr. in the U.S. and nearly throughout our range. Apr-May.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.