Alternanthera is a genus of flowering plants in the family Amaranthaceae. It is a widespread genus with most species occurring in the tropical Americas, and others in Asia, Africa, and Australia. Plants of the genus may be known generally as joyweeds, or Joseph's coat. Several species are notorious noxious weeds. Description These are annual or perennial herbs or subshrubs. While some of the better-known species are aquatic plants, most are terrestrial. 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. 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. Species It is not yet clear how many species belong in the genus. Estimates range between 80 and 200. Species include: Alternanthera acaulis Andersson Alternanthera adscendens Suess. Alternanthera albotomentosa Suess. Alternanthera albida (Moq.) Griseb Alternanthera albosquarrosa Suess. Alternanthera albotomentosa Suess. Alternanthera altacruzensis Suess. Alternanthera angustifolia R.Br. – narrow-leaf joyweed Alternanthera aquatica (Parodi) Chodat Alternanthera arequipensis Suess. Alternanthera areschougii Alternanthera asterotricha Uline Alternanthera axillaris (Willd.) DC. Alternanthera bettzickiana – calico-plant Alternanthera brasiliana (L.) Kuntze – Brazilian joyweed, ruby leaf Alternanthera caracasana Kunth – mat chaff-flower, washerwoman Alternanthera corymbiformis Alternanthera crucis Bold. – West Indian joyweed Alternanthera dentata – little ruby Alternanthera denticulata – lesser joyweed Alternanthera echinocephala (Hook.f.) Christoph. – spiny-headed chaff flower, sea-urchin joyweed Alternanthera ficoidea – parrot leaf Alternanthera filifolia (Hook.f.) J.T. Howell Alternanthera flavescens – yellow joyweed Alternanthera flavicoma Alternanthera galapagensis Alternanthera grandis Alternanthera hassleriana Chodat – Hassler's alternanthera Alternanthera helleri (B.L.Rob.) J.T.Howell Alternanthera littoralis P.Beauv. Alternanthera maritima (Mart.) A.St.-Hil. – seaside joyweed Alternanthera mexicana Alternanthera nahui Alternanthera nana – downy joyweed, hairy joyweed Alternanthera nesiotes Alternanthera nodiflora – common joyweed Alternanthera olivacea Alternanthera paronichyoides A.St.-Hil. – smooth joyweed Alternanthera philoxeroides (Mart.) Griseb. – alligator weed Alternanthera pubiflora Alternanthera pungens Alternanthera reineckii Briq. Alternanthera sessilis (L.) DC. – rabbit-meat, sessile joyweed Alternanthera snodgrassii Alternanthera subscaposa Alternanthera versicolor R.Br. Ecology Many species have