Justicia is a genus of flowering plants in the family Acanthaceae. There are 658 species with a further 611 species as yet unresolved by Kew.  They are native to tropical to warm temperate regions of the Americas, India and Africa. Common names include water-willow and shrimp plant, the latter from the inflorescences, which resemble a shrimp in some species. The generic name honours Scottish horticulturist James Justice (1698-1763). They are closely related to Pachystachys.
They are evergreen perennials and shrubs with leaves which are often strongly veined; but they are primarily cultivated for their showy tubular flowers in shades of whitre, cream, yellow, orange or pink. They are not hardy below 7 °C (45 °F), so may be grown under glass in frost-prone areas.
Justicia americana (American water-willow), is native to eastern North America north to southern Ontario; it is the hardiest species in the genus, hardy to USDA Plant Zone 4. Justicia ovata (looseflower water-willow) occurs nearly as far north, reaching Michigan.
Justicia brandegeeana (formerly Beloperone guttata, commonly called shrimp plant) is native to Mexico. It is hardy to −4 °C but will often recover in the spring after freezing back in USDA Plant Zone 8a.
Justicia carnea (formerly Jacobinia carnea, common names including Brazilian plume flower, flamingo flower, and jacobinia) is native to South America in southern Brazil, Paraguay and northern Argentina. It is hardy to −2 °C but will often recover in the spring after freezing back in USDA Plant Zone 8a.
Justicia procumbens is procumbent herb with angular stems, swollen at nodes, small ovate leaves, small purple flowers in terminal spikes, inserted didynamous stamens, and shortly bilobed stigmas.
Genera which have been brought into Synonymy with Justicia include Acelica, Adhatoda, Amphiscopia, Anisostachya, Aulojusticia, Averia, Beloperone, Calliaspidia, Calymmostachya, Chaetothylopsis, Chiloglossa, Cyphisia, Cyrtanthera, Cyrtantherella, Dianthera, Dimanisa, Drejerella, Duvernoia, Emularia, Ethesia, Glosarithys, Harnieria, Heinzelia, Hemichoriste, Heteraspidia, Ixtlania, Jacobinia, Kuestera, Libonia, Lophothecium, Lustrinia, Nicoteba, Orthotactus, Parajusticia, Petalanthera, Plagiacanthus, Plegmatolemma, Porphyrocoma, Psacadocalymma, Rhacodiscus, Rhiphidosperma, Rhyticalymma, Rodatia, Rostellaria, Rostellularia, Saglorithys, Salviacanthus, Sarotheca, Sericographis, Simonisia, Solenochasma, Stethoma, Tabascina, Thalestris, Thamnojusticia, and Tyloglossa.
- "Genus: Justicia L.". Germplasm Resources Information Network. United States Department of Agriculture. 2009-01-23. Retrieved 2010-05-26.
- Austin, Daniel F. (2004). Florida Ethnobotany. CRC Press. p. 381. ISBN 978-0-8493-2332-4.
- RHS A-Z encyclopedia of garden plants. United Kingdom: Dorling Kindersley. 2008. p. 1136. ISBN 1405332964.
- "Justicia". Integrated Taxonomic Information System. Retrieved 2010-09-20.
- Plant Systematics: Justicia