4a. Cerastium arvense Linnaeus subsp. arvense
Plants straggling and creeping, strongly rhizomatous, not forming clumps, without taproot. Stems: flowering stems ascending, proximal 1/ 2 often purple tinged, usually 25-30 cm, softly pubes-cent to subglabrous, glandular hairs confined to inflorescences; nonflowering shoots well devel-oped, producing obovate to oblanceolate, spatulate, overwintering leaves; small axillary tufts of leaves well developed, conspicuous. Leaves on flowering shoots often dimorphic; mid-stem leaves larger, blade lanceolate, 12-22 × 2.5-5 mm; proximal leaves oblong to linear, 5-15 × 0.5-2 mm.
Flowers: sepals 5-7 mm, with midrib; petals 10-12.5 mm, often turning brown when dried; anthers 1-1.1 mm. Capsules (8.5-)9.8(-11.5) × 3-4 mm, ca. 1.5(-2) times as long as sepals. Seeds 0.7-1.2 mm. 2n = 72.
Flowering spring. Lawns, cemeteries, roadsides, riverbanks, old pastures; 0-1400 m; introduced; Nfld. and Labr. (Nfld.), Ont., Que.; Conn., Md., Mass., N.J., N.Y.; w Europe.
Subspecies arvense is probably more widespread in North America than present information suggests, but identification of herbarium specimens can be difficult and uncertain. However, in the field the two subspecies are readily distinguishable because of the larger size of subsp. arvense and its strongly rhizomatous habit. Hybrids with C. tomentosum (which have been called C. ×maureri Schulze, an invalid name) are readily formed when the two taxa grow together (J. K. Morton 1973).