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annual knawel, German knotgrass, scléranthe annuel

German knotgrass, knawel, scléranthe

Habit 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 (50x).

Seeds

1, yellowish, globose, not compressed, smooth, marginal wing absent, appendage absent.

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.

x

= 11 [12].

Scleranthus annuus

Scleranthus

Distribution
from FNA
AL; AR; CA; CT; DC; DE; FL; GA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; NE; NH; NJ; NY; OH; OK; OR; PA; RI; SC; TN; VA; VT; WA; WI; WV; AB; BC; NB; NF; NS; ON; PE; QC; SK; Europe; w Asia; n Africa
[WildflowerSearch map]
[BONAP county map]
from USDA
temperate Europe (including Mediterranean region); Asia; Africa; Australia; widely naturalized elsewhere [Introduced in North America]
[BONAP county map]
Discussion

Subspecies 8 (1 in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species ca. 10 (2 in the flora).

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).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Key
1. Sepals with acute apices, spreading to erect in fruit, not overlapping, margins 0.1 mm or less wide; flowers usually equaling or shorter than bracts
S. annuus
1. Sepals with blunt or rounded apices, usually bending together in fruit, overlapping, margins 0.3-0.5 mm wide; flowers usually longer than bracts
S. perennis
Source FNA vol. 5, p. 150. FNA vol. 5, p. 149. Authors: John W. Thieret, Richard K. Rabeler.
Parent taxa Caryophyllaceae > subfam. Alsinoideae > Scleranthus Caryophyllaceae > subfam. Alsinoideae
Sibling taxa
S. perennis
Subordinate taxa
S. annuus subsp. annuus
S. annuus, S. perennis
Name authority Linnaeus: Sp. Pl. 1: 406. (1753) Linnaeus: Sp. Pl. 1: 406. 1753 (as Schleranthus): Gen. Pl. ed. 5, 190. (1754)
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