Alternanthera

Alternanthera is a genus of flowering plants in the family Amaranthaceae. It is a widespread genus with most species occurring in the tropical Americas,<ref name=san>Sánchez-Del Pino, I., et al. (2012). Molecular phylogenetics of Alternanthera (Gomphrenoideae, Amaranthaceae): resolving a complex taxonomic history caused by different interpretations of morphological characters in a lineage with C₄ and C₃–C₄ intermediate species. Botanical Journal of the Linnean Society 169(3), 493-517.</ref><ref name=fna>Alternanthera. Flora of North America.</ref> and others in Asia, Africa, and Australia.<ref name=fna/> Plants of the genus may be known generally as joyweeds, or Joseph's coat.<ref name=itis>Alternanthera. Integrated Taxonomic Information System (ITIS).</ref> Several species are notorious noxious weeds.<ref name=tan>Tanveer, A., et al. (2013). A review on genus Alternanthera weeds implications. Template:Webarchive Pak. J. Weed Sci. Res 19(1), 53-58.</ref>

Description

These are annual or perennial herbs or subshrubs. While some of the better-known species are aquatic plants, most are terrestrial.<ref name=tan/> 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.<ref name=fna/>

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.<ref name="SageSage2007">Template:Cite journal Template:Open access</ref><ref name=san/><ref name=chin>Chinthapalli, B., et al. (2001). Phosphoenolpyruvate carboxylase purified from leaves of C₃, C₄, and C₃-C₄ intermediate species of Alternanthera: Properties at limiting and saturating bicarbonate. Photosynthetica 38(3), 415-19.</ref>

Species

File:Alternanthera Party time.jpg

Alternanthera 'Party Time'

File:Alternanthera sessilis W2 IMG 3422.jpg

Alternanthera sessilis

File:Alternanthera polygonoides2.jpg

Alternanthera polygonoides

It is not yet clear how many species belong in the genus. Estimates range between 80 and 200.<ref name=san/><ref name=fna/><ref name=tan/><ref name=itis/><ref>GRIN Species Records of Alternanthera. Template:Webarchive Germplasm Resources Information Network (GRIN).</ref> Plants of the World Online accepts 106 species.<ref name = powo/>

As of April 2024, Plants of the World Online accepts the following species:<ref name = powo/> Template:Div col

• 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 Template:Small
• Alternanthera axillaris Template:Small
• Alternanthera bahiensis Template:Small
• Alternanthera bettzickiana Template:Small – calico-plant
• Alternanthera brasiliana (L.) Kuntze – Brazilian joyweed, ruby leaf
  • Alternanthera brasiliana var. villosa Template:Small (synonym Alternanthera dentata Template:Small) – little ruby
• Alternanthera calcicola Template:Small
• Alternanthera cana Template:Small
• Alternanthera canescens Template:Small
• Alternanthera caracasana Kunth – mat chaff-flower, washerwoman
• Alternanthera cinerella Template:Small
• Alternanthera collina Template:Small
• Alternanthera congesta Template:Small
• Alternanthera cordobensis Template:Small
• Alternanthera corymbiformis Template:Small
• Alternanthera costaricensis Template:Small
• Alternanthera crassifolia Template:Small
• Alternanthera decurrens Template:Small
• Alternanthera dendrotricha Template:Small
• Alternanthera denticulata Template:Small – lesser joyweed
• Alternanthera dominii Template:Small
• Alternanthera ebracteolata Template:Small
• Alternanthera echinocephala (Hook.f.) Christoph. – spiny-headed chaff flower,<ref name=McMu99>Template:Cite book, p. 144</ref> sea-urchin joyweed
• Alternanthera fasciculata Template:Small
• Alternanthera fastigiata Template:Small
• Alternanthera ficoidea Template:Small – parrot leaf
• Alternanthera filifolia (Hook.f.) J.T.Howell
• Alternanthera flava Template:Small
• Alternanthera flavescens Template:Small – yellow joyweed
• Alternanthera flavicoma Template:Small
• Alternanthera flavida Template:Small
• Alternanthera flosculosa Template:Small
• Alternanthera galapagensis Template:Small
• Alternanthera geniculata Template:Small
• Alternanthera glaziovii Template:Small
• Alternanthera grandis Template:Small
• Alternanthera halimifolia Template:Small – West Indian joyweed
• Alternanthera helleri (B.L.Rob.) J.T.Howell
• Alternanthera herniarioides Template:Small
• Alternanthera hirtula Template:Small
• Alternanthera inaccessa Template:Small
• Alternanthera indica Template:Small
• Alternanthera ingramiana Template:Small
• Alternanthera jacquinii Template:Small
• Alternanthera januarensis Template:Small
• Alternanthera kanhae Template:Small
• Alternanthera kurtzii Template:Small
• Alternanthera laguroides Template:Small
• Alternanthera lanceolata Template:Small
• Alternanthera laxa Template:Small
• Alternanthera littoralis P.Beauv. – seaside joyweed
• Alternanthera lupulina Template:Small
• Alternanthera macbridei Template:Small
• Alternanthera martii Template:Small
• Alternanthera micrantha Template:Small
• Alternanthera microphylla Template:Small
• Alternanthera minutiflora Template:Small
• Alternanthera mollendoana Template:Small
• Alternanthera multicaulis Template:Small
• Alternanthera nahui Template:Small
• Alternanthera nesiotes Template:Small
• Alternanthera nodiflora Template:Small – common joyweed
• Alternanthera obovata Template:Small
• Alternanthera olivacea Template:Small
• Alternanthera panamensis Template:Small
• Alternanthera paronichyoides A.St.-Hil. – smooth joyweed
• Alternanthera pennelliana Template:Small
• Alternanthera peruviana Template:Small
• Alternanthera philippo-coburgii Template:Small
• Alternanthera philoxeroides (Mart.) Griseb. – alligator weed
• Alternanthera porrigens Template:Small
• Alternanthera praelonga Template:Small
• Alternanthera puberula Template:Small
• Alternanthera pubiflora Template:Small
• Alternanthera pulchella Template:Small
• Alternanthera pulverulenta Template:Small
• Alternanthera pumila Template:Small
• Alternanthera pungens Template:Small
• Alternanthera pycnantha Template:Small
• Alternanthera raimondii Template:Small
• Alternanthera regelii Template:Small
• Alternanthera reineckii Briq.
• Alternanthera robinsonii Template:Small
• Alternanthera rufa Template:Small
• Alternanthera rugulosa Template:Small
• Alternanthera serpens Template:Small
• Alternanthera serpyllifolia Template:Small
• Alternanthera sessilis (L.) DC. – rabbit-meat, sessile joyweed, downy joyweed, hairy joyweed
• Alternanthera snodgrassii Template:Small
• Alternanthera spinosa Template:Small
• Alternanthera stellata Template:Small
• Alternanthera stenophylla Template:Small
• Alternanthera suessenguthii Template:Small
• Alternanthera tetramera Template:Small
• Alternanthera tomentosa Template:Small
• Alternanthera tubulosa Template:Small
• Alternanthera vestita Template:Small
• Alternanthera villosa Template:Small

Formerly placed here

• Gomphrena subscaposa Template:Small (as Alternanthera subscaposa Template:Small)

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.<ref name=tan/> The most important species is alligator weed (A. philoxeroides), a South American aquatic plant that has spread to other continents.<ref name=tan/> 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.<ref name=tan/> Alternanthera plants are known to produce allelopathic compounds that injure other plants, including crops.<ref name=tan/>

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).<ref name=tan/>

Uses

A. philoxeroides and A. sessilis are eaten as vegetables in parts of Asia.<ref name=tan/>

Some Alternanthera are used as ornamental plants.<ref name=tan/>