Xanthium orientale L. var. italicum (Moretti) M.Hassl.

Global description

Xanthium orientale var. italicum is a herbaceous to sub-woody annual plant, much branched, growing up to 2 m tall. The erect stems are brownish or reddish-brown, often red-spotted, ribbed and roughly-hairy but without spines. The leaves, petiolate, are simple, broad-ovate to triangular, 3-5-lobed, dull green, with serrated margins and short bristly hairs on both sides, they are scabrous on the upper face, and widely cuneate at base. The upper leaf surface is darker than the underside and prominently 3-veined with purplish veins. The creamy or yellowish green flowers are inconspicuous, unisexual, and arranged in terminal and axillary heads. The fruit is an ellipsoid brownish bur, crowned with two stout horns and covered with hooked spines.

Cotyledons

Cotyledons are elliptical to linear, very large, 35-60 mm long and 6-10 mm wide. They are fleshy, glabrous, with a visible main vein and a short, canaliculate petiole that is sheathing at the base. The margin is entire.

First leaves

The first leaves are simple and opposite, long petiolate. The primordial leaves are oval-lanceolate, with a toothed margin. The following leaves are triangular, deeply toothed to almost lobed, covered with stubby, stiff, flattened hairs. The upper surface is scabrous. The hypocotyledonous axis is developed, thick, and often coloured pink near the collar. The seedling is greyish green and rough to the touch.

General habit

A much branched annual bushy herb, growing up to 1-2 m tall.

Underground system

Taproot system

Stem

The branches are without spines. The erect stems are brownish or reddish-brown, often red-spotted, ribbed and roughly-hairy.

Leaves

Leaves borne on petioles, 2-12 cm long. Simple, broadly deltate, up to 18 cm long x 18 cm wide, irregularly lobed, base widely cuneate, dull green, with serrated margins and short bristly hairs on both sides. The upper leaf surface is darker than the underside and prominently 3-veined with purplish veins, nd hardly scabrous. The leaves are opposite at the base of the plant and alternate in the upper portion.

Inflorescence

The flowers are unisexual with separate male and female flowers on the same plant. The male flowers are clustered in capitulums at the end of the branches or in the upper leaf forks; the female flower occur in the leaf junctions.

Flower

Male flowers are cream to creamy green. Female flowers are yellowish green to brownish. The corolla is tubular; stamens free. In stalked axillary clusters. The female heads consist of two pistillate flowers surrounded by a spiny involucre.

Fruit

Upon fruiting, the two female flowers ripen into two brown to black achenes, one larger than the other, and they are completely enveloped by the involucre, which becomes an ellipsoid bur, 17-25 mm long and 7-15 mm width (comprising hooked spines) green at first, it turns yellowish then brow; it bears two stout, curved or straight horns at the top (5-12 mm long) and numerous thin and elongated spines with hooked tips, as long as the fruit diameter. One bur contains 2 compartments with one seed each.

Seed

One achene per floret, two per bur; 1-1.5 cm long and 4-6 mm width; dark-brown, oblong and flattened with pointed apex, no pappus; seeds germinate in successive years.

Origin

Xanthium orientale var. italicum is native to temperate to subtropical regions of North and South America.

Worldwide distribution

This species is considered to have been introduced into the northern part of South America (not recorded in French Guiana), it has also been introduced into the Caribbean (not recorded in the West Indies), all the countries of the Mediterranean basin, the whole of northern Europe, southern Africa, India.

https://www.gbif.org/species/11519882