Vernacular
  • Large purple alternanthera
  • Sessile flowered globe amaranth
  • Sessile joyweed
Details
Eppo_code

ALRSE

Family

Amaranthaceae

Species

Alternanthera sessilis (L.) R.Br. ex DC.

Meaning_of_the_name

Alternanthera - alterno means alternate, anthera means flowers; sessilis: without a stalk (probably referring to the inflorescences)

Global_description

Alternanthera sessilis is a many-branched, perennial, sometimes annual, herb. It can be erect or prostrate, rooting at the nodes, or may occasionally be a floating or emergent aquatic. The stems are greenish, pink to purplish, ribbed, up to 1 m, mostly glabrous except for tufts of white hairs in the branch and leaf axils. The young stems have a line of hairs down each side. The leaves are simple, opposite, subsessile, entire, linear-lanceolate to obovate-spathulate but very variable in shape. The inflorescences are sessile, in the leaf axils, often in clusters; they are whitish and non-spiny.

Similar_species
Cotyledons
First_leaves
Habit

Perennial herb, many-branched. Its habit and dimensions vary greatly depending on the humidity level: in dry conditions, it is erect and can reach 30 cm in length; in wet conditions, it is prostrate, then erect with stems 10cm-1 m long. In flooded areas, it is a floating herb reaching several meters in length .

Underground_system

Main root is a taproot, white or brown. When the plant is prostrate, adventitious roots appear at the nodes creeping on the ground. In aquatic conditions, bundles of long white roots are borne from the nodes.

Stem

Cylindric, many-branched, villous in lines and transversely at the nodes. Solid and thin in dry conditions, the stem is longer, hollow and floating in aquatic conditions, reaching 1 cm in diameter.
It is glabrous except for two opposite narrow lines of whitish hairs on the erect parts, and tufts of white hairs at the nodes.

Leaves

Leaves are simple, opposite and decussate; paired blades are generally the same size. Petiole is indistinct, short (1.5 mm) or absent. The laminas are narrow and elongated, very variable in shape and size. Oblanceolate to elliptic-lanceolate or linear-lanceolate, apex acute to obtuse, shortly acuminate, base cuneate to attenuate, 1 to 12 cm long and 0.25 to 3 cm wide; glabrous or nearly so, with sparse hairs mostly found on the lower side, on the midrib.

Inflorescence

Inflorescences are sessile spikes, in the axils of leaves, isolated or grouped (up to 5), subglobose, to 1 cm across with segments to 2.5 mm long.

Flowers

Each flower is subtended by a white scarious bract, 0.75-1 mm long with a pointed end, and 2 bracteoles similar to the bract. The perianth consists of tepals, all equal, ovate-elliptic, pointed at the apex, 1.5 to 2.5 mm long, white, glabrous, distinctly mucronate, with a slightly denticulate margin.Five stamens (including 2 without anther) alternate with pseudostaminodes similar to filaments, but usually a bit smaller. At maturity, they equal the ovary and style. The ovary iscompressed, sub-orbicular, with a short style.

Fruits

The fruit is a utricle, obcordate to orbicular-obcordate, 2 to 3 mm long, dark brown with paler edge. It falls with the tepals.

Seeds

Lens-shaped, 0.5 to 1 mm in diameter, testa bright brown, slightly reticulate.

Biology

Herbaceous plant that can be annual or perennial depending on the humidity of the environment.
Spread by seed or by vegetative propagation. Fruits are dispersed by ants.

Ecology

The plant grows preferably in wet soil, along ditches, seasonally waterlogged roadside depressions, fallow lands, lakes, marshes, irrigation canals, rice field levees and in waterways, up to 1,250 m altitude.

Origine
World_distribution
South_african_distribution
Knp_distribution
Use
Global_weediness
South_african_weediness
Knp_weediness
Global_control
Control_knp
References

-Foxcroft et al. 2003. A revised list of alien plants for the KNP.
-Flora of Zimbabwe : Hyde, M.A., Wursten, B.T. & Ballings, P. (2013). Flora of Zimbabwe: Species information: Alternanthera sessilis.
-Swaziland’s Alien Plants Database
-Global Invasive Species Database
-Pacific Island Ecosystems at Risk (PIER)
-Afroweeds
-Adventilles

Web_links

http://www.zimbabweflora.co.zw/speciesdata/species.php?species_id=122550
http://www.sntc.org.sz/alienplants/speciesinfo.asp?spid=40
http://www.issg.org/database/species/ecology.asp?si=767&fr=1&sts=sss&lang=EN
http://www.hear.org/pier/species/alternanthera_sessilis.htm

Vernacular Country Language Source
Sessile flowered globe amaranth English R.P.Randall, 2002
Large purple alternanthera English Foxcroft, 2003
Sessile joyweed English R.P.Randall, 2002
Map