29. Scleranthus Linnaeus, Sp. Pl. 1: 406. 1753. (as Schleranthus); Gen. Pl. ed. 5, 190. 1754.
Knawel, scléranthe [Greek skleros, hard, and anthos, flower, alluding to the indurate hypanthium]
John W. Thieret, Richard K. Rabeler
Herbs, annual, biennial, or perennial. Taproots slender. Stems erect to prostrate, branched, terete. Leaves connate proximally, sessile; blade 1-veined, subulate to linear, not succulent, apex acute or obtuse. Inflorescences terminal or axillary, lax to dense cymes; bracts paired, foliaceous. Flowers sessile to subsessile; perianth and androecium perigynous; hypanthium urceolate, abruptly expanded distally; sepals 5, distinct, greenish, lanceolate to awl-shaped, 1.5-4 mm, herbaceous, margins whitish, scarious, apex acute to blunt or obtuse; petals absent; nectariferous disc at base of stamens; stamens 2-10, arising from hypanthium rim; filaments distinct; staminodes absent or 5-8, arising from hypanthium rim, filiform; styles 2, capitate, 0.8-1 mm, glabrous proximally; stigmas 2, terminal, minutely papillate (50×). Utricles ovoid, enclosed in persistent, indurate, shallowly or strongly furrowed, sepal-crowned hypanthium and falling with it, the whole constituting the indehiscent “fruit”; carpophore present. Seeds 1, yellowish, globose, not compressed, smooth, marginal wing absent, appendage absent. x = 11 .
Species ca. 10 (2 in the flora): introduced; temperate Europe (including Mediterranean region), Asia, Africa, Australia; widely naturalized elsewhere.
In spite of their small size, most Scleranthus flowers secrete nectar and are visited by insects, including small flies and ants. Pollination in species within the flora area varies from chiefly protandrous outcrossing (S. perennis) to chiefly autogamous (S. annuus). L. Svensson (1988) reported that these two species hybridize regularly in Europe, producing flowers with ten reduced, sterile stamens.
The common name “knawel” apparently refers to the glomerules of flowers (German Knäuel).
Smissen, R. D. and P. J. Garnock-Jones. 2002. Relationships, classification and evolution of Scleranthus (Caryophyllaceae) as inferred from analysis of morphological characters. Bot. J. Linn. Soc. 140: 15-29.