Polycarpon

Herbs, annual. Taproots slender. Stems prostrate to erect, branched, terete to finely ridged. Leaves opposite or in whorls of 4, not connate, petiolate; stipules 2 per node, silvery, lanceolate to triangular-ovate, margins entire or irregularly cut, apex acuminate to aristate; blade 1-veined, spatulate or oblanceolate to ovate or elliptic, not succulent, apex obtuse, sometimes mucronate. Inflorescences terminal or axillary, dense or lax cymes; bracts paired or absent. Pedicels erect. Flowers: perianth and androecium perigynous; hypanthium minute, cup-shaped, not abruptly expanded distally; sepals distinct, green, lanceolate to elliptic or ovate, often keeled, 1–2.5 mm, herbaceous, margins white, scarious, apex acute, ± hooded, ± awned; petals often fugacious, 5, white, blade apex emarginate; nectaries between filament bases; stamens 3–5; filaments shortly connate distally around ovary; style 1, obscurely 3-branched, filiform, 0.1–0.3 mm, glabrous proximally; stigmas 3, linear along adaxial surface of style branches, papillate (30×). Capsules ovoid to spherical, opening by 3 incurved or twisting valves; carpophore present. Seeds ca. 8–15, whitish, ovoid to lenticular or triangular, laterally compressed to angular, papillate or granular, marginal wing absent, appendage absent. x = [7], 8, 9.

Distribution

w North America, South America, Europe (including Mediterranean region), Asia, Africa, Polycarpon tetraphyllum introduced widely, including e North America, Australia.

Discussion

Species ca. 9 or 15 (2 in the flora).

C. Mohr’s (1901) report of Polycarpon alsinifolium (Bivona-Bernardi) de Candolle from Alabama was based on misidentification of P. tetraphyllum subsp. tetraphyllum.

The shape of the sepal apex in Polycarpon is varied, with the herbaceous central portion sometimes prolonged beyond the scarious margins into a brief, narrow hood or awn, suggesting an aristate apex.

Selected References

Howell, J. T. 1941. Notes on Polycarpon. Leafl. W. Bot. 3: 80.

Lower Taxa

Polycarpon depressum, Polycarpon tetraphyllum

Key

1	Sepals 1.5-2.5 mm, keeled; stipules 1.8-2.8 mm; leaves in whorls of 4 or opposite	Polycarpon tetraphyllum
1	Sepals 1-1.5 mm, flat or sometimes barely keeled; stipules 0.4-1.2 mm; leaves opposite, not whorled	Polycarpon depressum