Annual knawel (Scleranthus annuus)

Classification

Kingdom: Plants (Plantae)

Division: Flowering plants (Angiosperms) (Angiospermae)

Class: Dicotyledons (Dicotyledoneae)

Order: Caryophyllales (Caryophyllales)

Family: Carnation family (Caryophyllaceae)

Genus: Knawel (Scleranthus)

Species: Annual knawel (Scleranthus annuus L.)

Synonyms

• Knavel annuum Scop.

Origin

Native to Europe.

Similar species

Scleranthus perennis. Native to Europe, found on roadsides and sandy sites in the north‑eastern United States and Canada. It is distinguished by its woody base, bracts shorter than the flowers, leaves 3–13 mm long and overlapping sepals 2.5–4 mm long.

Root system

Taproot system, relatively weak. Roots stiff, fibrous, penetrating to a depth of 25 cm.

Seeds

Seeds light brown, oval, about 2 mm long.

Seedlings

Seedlings with flat, narrow, linear cotyledons, 8–12 mm long, 2–5 mm wide, somewhat fleshy.

First leaves 5–20 mm long, 1–2 mm wide.

Leaves

Leaves opposite, awl‑shaped, narrowly linear or thread‑like, 5–24 mm long, 1–1.5 mm wide, sharply pointed, glabrous or hairy, sessile. At the base they are fused in pairs and ciliate, sometimes with a cluster of leaves in the axils.

Margins with a few hairs and transparent membranous edges at the base.

Stems

Stems weak, erect or spreading, branched from the base, brown‑green, covered with short hairs.

Nodes hairy.

Height (2.5) 5–25 cm.

Inflorescence

Inflorescence a semi‑umbel (false umbel, glomerule).

Flowers green, sessile, 4–5 mm across, shorter than the bracts, borne at the ends of stems or in leaf axils.

Calyx glabrous, 5 sepals, 3–4 mm long, partly fused. Calyx teeth spreading at fruit maturity.

Petals absent.

8–10 stamens. 1 pistil. 2 stigmas. 2 filiform styles.

Fruit

Ovoid, globose or elongated capsule (nutlet), 3.2–5 mm long, 1.5 mm wide, enclosed by the hardened calyx. One‑seeded.

The fruit falls off at maturity but does not open.

Natural zones

Annual knawel is widespread, especially in the taiga zone.

Light requirements

Tolerates light shade.

Soil requirements

An oxylophytic weed, i.e. it prefers acid soils with <abbr title="Hydrogen ion concentration">pH</abbr> below 5.

Habitats

Plants form mats.

Sandy soils, fallow land, heaths, roadsides, dry stony and gravelly slopes, in crops.

In the taiga zone it occurs in all crops, but most often in winter rye and flax, sometimes forming a continuous cover under their canopy. In the forest‑steppe and especially steppe zones it loses its importance as a segetal weed and occurs as a ruderal along roads, on fallows and in other weedy places.

Germination

Longevity unknown.

Seed germination good.

Maximum germination depth 5–7 cm.

Germination occurs at soil temperatures of 18 to 20 °C.

Growth cycle

Flowering April–August. Fruiting from June.

Reproduction

Reproduces by seeds.

Plants can produce up to 100 seeds (Dickinson), according to other data up to 2000 seeds (Bazdyrev).

Weight of 1000 nutlets – up to 3 g.

Regions of distribution

Russia:

• European part – all regions;
• North Caucasus – all regions;
• Far East – all regions.

Belarus, Ukraine, Moldova, Lithuania, Latvia, Estonia, Georgia, Armenia, Azerbaijan – all regions.

Kazakhstan: West Kazakhstan Region (west), Atyrau Region (west).

Weed infestation of crops

A weed of cereals, row crops, vegetables and industrial crops.

To the south its harmfulness decreases.

Fodder value

Annual knawel is readily eaten by goats, selectively by horses; sheep and cattle do not eat it.

Indicator plant

Can serve as an indicator of increased soil acidity.

Agronomic methods

The roots are stiff, so they can withstand light cultivation.

Agronomic measures include thorough autumn soil tillage.

Stale seedbed techniques, i.e. creating optimal conditions for germination in spring and autumn followed by destruction, are effective.

Observing crop rotation also helps reduce the weed population.

Chemical methods

Annual knawel is resistant to herbicides 2,4-D and 2M‑4X.

For chemical control, dialen, lontrel, diamet‑D and soil‑applied herbicides may be used.