Xanthium spinosum L.

Global description

Xanthium spinosum is an erect plant, branched from the base and pubescent. The leaves are simple, alternate, short-petiolate, with an entire or 3-5-lobed blade, the terminal blade long lanceolate. At the base of the leaves are long yellow spines with 3 branches. The lower face of the leaves is tomentose. The flowers are axillary and terminal in small groups. The fruit is an elliptical capsule bristling with hooked yellow spines and bearing 2 short, very unequal, straight spines at the top.

Cotyledons

The cotyledons are fleshy and petiolate. The blade is spatulate with a rounded apex and a long, attenuated base. They are 2.5 to 3.5 cm long and 6 to 8 mm wide. They are smooth, hairless and greenish in colour.

First leaves

The first leaves are simple, opposite and decussate. They are petiolate. The blade is oblong, with an irregular margin, smooth and hairless; light green with yellowish veins. Basal lobes appear from the second leaf onwards. Stiff, pointed spines appear at the base of the petioles from leaf level 4 or 6 onwards.

General habit

Xanthium spinosum is an upright herbaceous or semi-shrubby plant, 30 to 60 cm high, but which can reach 1.5 m. It branches from the base.

Underground system

The root is a deep taproot that is very difficult to dig out.

Stem

The stem is cylindrical and solid, becoming subligneous at the base. It is abundantly branched from the base and is yellowish-green in colour, glabrous or shortly pubescent in the young parts. Rigid yellow spines, 1 to 4 cm long and generally with 3 divergent branches, are present at the base of the leaves and at the branches.

Leaf

The leaves are simple, opposite at the base of the plant and then rapidly alternate. They are petiolate. The leaf blade is generally oval lanceolate, 15 to 12 cm long and 2 to 4 cm wide, generally three-lobed, with an elongated central lobe and 2 reduced lateral lobes or sometimes 5-lobed. The apex of the blade and lobes is acuminate and the base is broadly wedge-shaped. The leaf blade is leathery, dark green on the upper side with tomentose white veins and greyish green and tomentose on the lower side. The veins are clearly visible and light in colour.

Inflorescence

The male flower heads are grouped in terminal glomerules, while the female flower heads are in small groups in the leaf axils.

Flower

The male flower heads are globose, 5 mm in diameter, surrounded by non-spiny scales. Each flower head contains around ten inconspicuous florets, formed by a greenish tubular corolla containing 5 free stamens.
The female flower heads are assembled in pairs inside an oval involucral body formed by the fused involucral bracts with a large number of sharp points that become rigid at maturity. The female florets have no corolla and are reduced to an ovary topped by a yellow stigma.

Fruit

The fruit is an ovoid to ellipsoid capsule, corresponding to the hardened involucre of the female flower head (11 to 12 mm long, 3.5 to 4 mm wide and 2.5 to 3 mm thick excluding the spines), and bristling with numerous spines with a broad base, hooked top and short woolly hairs and two straight, inconspicuous tips of unequal length at the top. The fruits are attached in small, sessile groups to the leaf axils. Each fruit has 2 compartments containing one seed. When ripe, they take on a yellow-orange colour.

Seed

Each fruit compartment contains a compressed fusiform achene, 9 to 10 mm long and 2 mm wide, with a dull black striated surface.

Origin

Xanthium spinosum is native to North and South America, particularly in regions with a temperate or subtropical climate.

Worldwide distribution

This species has been introduced into Europe as far as India and the countries of the Mediterranean basin, southern Africa, eastern and northern China and Australia. It is only occasionally found in the Mascarene Islands (Mauritius, Rodrigues and Réunion).

https://www.gbif.org/species/3089150