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Alternanthera
	Alternanthera caracasana (khakiweed)
	Alternanthera bettzickiana (calicoplant)
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Order:	Caryophyllales
Family:	Amaranthaceae
Subfamily:	Gomphrenoideae
Genus:	Alternanthera; Forssk. (1775)
Species
	80-200, see text
Synonyms
	Adoceton Raf. (1817); Adoketon Raf. (1817); Allaganthera Mart. (1814); Amarantesia Regel (1869); Brandesia Mart. (1826); Bucholzia Mart. (1826); Everion Raf. (1838); Jeilium Regel (1869); Mogiphanes Mart. (1826); Pityranthus Mart. (1817); Steiremis Raf. (1837); Telanthera R.Br. (1818);

Alternanthera is a genus of flowering plants in the family Amaranthaceae. It is a widespread genus with most species occurring in the tropical Americas,^[2]^[3] and others in Asia, Africa, and Australia.^[3] Plants of the genus may be known generally as joyweeds, or Joseph's coat.^[4] Several species are notorious noxious weeds.^[5]

Description

These are annual or perennial herbs or subshrubs. While some of the better-known species are aquatic plants, most are terrestrial.^[5] They take many forms, from prostrate to erect to floating. The leaves are oppositely arranged. The inflorescence is a spike or a rounded head occurring in the leaf axils or the ends of branches. The flowers have 5 tepals. There are 3 to 5 stamens which are fused into a rim at the bases, and 5 pseudostaminodes, appendages between the stamens that are not true staminodes. The fruit is a utricle containing one seed.^[3]

The genus Alternanthera contains both terrestrial and aquatic species. The photosynthetic pathway varies in this genus: Some species undergo C₃ carbon fixation, one clade of 17 species has acquired the C₄ pathway, and yet other species have an intermediate C₃-C₄ pathway.^[6]^[2]^[7]

Species

It is not yet clear how many species belong in the genus. Estimates range between 80 and 200.^[2]^[3]^[5]^[4]^[8] Plants of the World Online accepts 106 species.^[1]

As of April 2024, Plants of the World Online accepts the following species:^[1]

Alternanthera albida (Moq.) Griseb.
Alternanthera albosquarrosa Suess.
Alternanthera albotomentosa Suess.
Alternanthera altacruzensis Suess.
Alternanthera angustifolia R.Br. – narrow-leaf joyweed
Alternanthera aquatica (D.Parodi) Chodat – Hassler's alternanthera
Alternanthera arequipensis Suess.
Alternanthera areschougii R.E.Fr.
Alternanthera axillaris (Willd.) DC.
Alternanthera bahiensis Pedersen
Alternanthera bettzickiana (Regel) G.Nicholson – calico-plant
Alternanthera brasiliana (L.) Kuntze – Brazilian joyweed, ruby leaf
- Alternanthera brasiliana var. villosa (Moq.) Kuntze (synonym Alternanthera dentata Stuchlík ex R.E.Fr.) – little ruby
Alternanthera calcicola Standl.
Alternanthera cana Suess.
Alternanthera canescens Kunth
Alternanthera caracasana Kunth – mat chaff-flower, washerwoman
Alternanthera cinerella Suess.
Alternanthera collina Pedersen
Alternanthera congesta Suess. & O.Stützer
Alternanthera cordobensis (Standl.) Standl.
Alternanthera corymbiformis Eliasson
Alternanthera costaricensis Kuntze
Alternanthera crassifolia (Standl.) Alain
Alternanthera decurrens J.C.Siqueira
Alternanthera dendrotricha C.C.Towns.
Alternanthera denticulata R.Br. – lesser joyweed
Alternanthera dominii Schinz
Alternanthera ebracteolata Sindhu Arya & V.S.A.Kumar
Alternanthera echinocephala (Hook.f.) Christoph. – spiny-headed chaff flower,^[9] sea-urchin joyweed
Alternanthera fasciculata Suess.
Alternanthera fastigiata Suess.
Alternanthera ficoidea (L.) P.Beauv. – parrot leaf
Alternanthera filifolia (Hook.f.) J.T.Howell
Alternanthera flava (L.) Mears
Alternanthera flavescens Kunth – yellow joyweed
Alternanthera flavicoma (Andersson) J.T.Howell
Alternanthera flavida Suess.
Alternanthera flosculosa J.T.Howell
Alternanthera galapagensis (A.Stewart) J.T.Howell
Alternanthera geniculata Urb.
Alternanthera glaziovii R.E.Fr.
Alternanthera grandis Eliasson
Alternanthera halimifolia (Lam.) Standl. ex Pittier – West Indian joyweed
Alternanthera helleri (B.L.Rob.) J.T.Howell
Alternanthera herniarioides Beurl.
Alternanthera hirtula (Mart.) R.E.Fr.
Alternanthera inaccessa Pedersen
Alternanthera indica Sindhu Arya, V.S.A.Kumar, Sánch.Pino & Iamonico
Alternanthera ingramiana (Standl.) Schinz
Alternanthera jacquinii (Schrad.) Alain
Alternanthera januarensis J.C.Siqueira
Alternanthera kanhae Vanzara, Katara & Nagar
Alternanthera kurtzii Schinz ex Pedersen
Alternanthera laguroides (Standl.) Standl.
Alternanthera lanceolata (Benth.) Schinz
Alternanthera laxa Suess.
Alternanthera littoralis P.Beauv. – seaside joyweed
Alternanthera lupulina Kunth
Alternanthera macbridei Standl.
Alternanthera martii (Moq.) R.E.Fr.
Alternanthera micrantha R.E.Fr.
Alternanthera microphylla R.E.Fr.
Alternanthera minutiflora (Seub.) Suess.
Alternanthera mollendoana Suess.
Alternanthera multicaulis (Mart.) Kuntze
Alternanthera nahui Heenan & de Lange
Alternanthera nesiotes I.M.Johnst.
Alternanthera nodiflora R.Br. – common joyweed
Alternanthera obovata (M.Martens & Galeotti) Millsp.
Alternanthera olivacea (Urb.) Urb.
Alternanthera panamensis (Standl.) Standl.
Alternanthera paronichyoides A.St.-Hil. – smooth joyweed
Alternanthera pennelliana Mears ex Pedersen
Alternanthera peruviana (Moq.) Suess.
Alternanthera philippo-coburgii (Zahlbr. ex Wawra) Suess.
Alternanthera philoxeroides (Mart.) Griseb. – alligator weed
Alternanthera porrigens (Jacq.) Kuntze
Alternanthera praelonga A.St.-Hil.
Alternanthera puberula (Mart.) D.Dietr.
Alternanthera pubiflora (Benth.) Kuntze
Alternanthera pulchella Kunth
Alternanthera pulverulenta Moq.
Alternanthera pumila O.Stützer
Alternanthera pungens Kunth
Alternanthera pycnantha (Benth.) Standl.
Alternanthera raimondii Suess.
Alternanthera regelii (Seub.) Schinz
Alternanthera reineckii Briq.
Alternanthera robinsonii Suess.
Alternanthera rufa (Mart.) D.Dietr.
Alternanthera rugulosa (B.L.Rob.) J.T.Howell
Alternanthera serpens Pedersen
Alternanthera serpyllifolia (Poir.) Urb.
Alternanthera sessilis (L.) DC. – rabbit-meat, sessile joyweed, downy joyweed, hairy joyweed
Alternanthera snodgrassii (B.L.Rob.) J.T.Howell
Alternanthera spinosa (Hornem.) Schult.
Alternanthera stellata (S.Watson) Uline & W.L.Bray
Alternanthera stenophylla (Standl.) Standl.
Alternanthera suessenguthii Covas
Alternanthera tetramera R.E.Fr.
Alternanthera tomentosa (Moq.) Schinz
Alternanthera tubulosa Suess.
Alternanthera vestita (Andersson) J.T.Howell
Alternanthera villosa Kunth

Formerly placed here

Gomphrena subscaposa (Hook.f.) T.Ortuño & Borsch (as Alternanthera subscaposa Hook.f)

Ecology

Many species have been reported as noxious weeds, including A. angustifolia, A. caracasana, A. denticulata, A. nana, A. nodiflora, A. paronychioides, A. philoxeroides, A. sessilis, A. tenella, and A. triandra.^[5] The most important species is alligator weed (A. philoxeroides), a South American aquatic plant that has spread to other continents.^[5] It is a weed of many kinds of agricultural crops, it is an invasive species that degrades native habitat, and its dense mats of vegetation clog waterways, slowing shipping and increasing flooding.^[5] Alternanthera plants are known to produce allelopathic compounds that injure other plants, including crops.^[5]

Biological pest control agents now in use to reduce alligator weed infestations include the alligator weed flea beetle (Agasicles hygrophila), the alligator weed thrips (Amynothrips andersoni), and the alligator weed stem borer (Arcola malloi).^[5]