Vernoniastrum ambiguum (Kotschy & Peyr.) H.Rob.

Global description

Vernoniastrum ambiguum is an erect plant that develops into a bushy tuft. The whole plant is pubescent. The leaves are alternate and simple. Those of the base have a limb attenuated in pseudo-petiole while those of the summit are embracing. Their margin is finely toothed. The inflorescence is composed of clusters of blue to purple flower heads. The achenes of light brown color, bear a pappus whose outer row is formed of scales surmounted by a long silk.

Cotyledons

The cotyledons are large. They are 25 mm long and 10 mm wide. They are obovally shaped. The base is attenuated in corner and the top is rounded. The first ribs are clearly visible.

First leaves

The first leaves are simple and alternate. They are obovate, elongated. The base of the limb is long attenuated in pseudo-petiole, the summit is rounded. The margin is finely denticulate. They are pubescent.

General habit

Vernoniastrum ambiguum is an erect plant. This one is very ramified from the very beginning. It is 25 to 50 cm high.

Underground system

The root is a taproot.

Stem

The stem is cylindrical, full. It is pubescent and covered with fine longitudinal wrinkles. In older plants, the base of the stem is sublime.

Leaf

The leaves are alternate and simple. In the lower part of the plant, they are oblanceolate, with a long attenuated base in pseudo-petiole. Those of the upper part of the plant are sessile with an enlarged base and slightly embracing. The edges are almost parallel and the margin is finely toothed. The leaves are 5 to 10 cm long and 1 to 3 cm wide. The summit is rounded. The limb has 6 to 12 conspicuous lateral veins. Both sides are finely pubescent. There is a well developed leaf at the base of each branch, to the top of the plant.

Infloresecence

The flowers are assembled in capitules arranged in clusters at the end of leafy branches. These flower heads measure 10 to 15 mm in diameter and are borne by peduncles whose length does not exceed the leaves. The involucre is composed of several rows of linear to lanceolate bracts. They are covered with a white pubescence and have a very dark acute summit. The flower head has only tubular flowers that are 8 mm long and have a purple to purplish-blue corolla.

Fruit

The fruits are achenes 2 mm long, with narrowed base and rounded apex. They are marked longitudinally by 4 or 5 strong wrinkles whose angles are pubescent and hollow tuberculous. The top of the achene is surmounted by a pappus comprising several rows of bristles 6 to 8 mm long. The outer bristles have at their base a membranous shell 1 mm long. The mature achenes are light brown in color.

Worldwide distribution

Vernoniastrum ambiguum is widespread throughout the dry areas of tropical Africa, from West Africa to Sudan and East Africa.

https://www.gbif.org/fr/species/3124518