''Petalophyllum americanum'', common name petalwort, is a species of liverwort in the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Fossombroniales Fossombroniales is an order of liverwort The Marchantiophyta () are a division of non-vascular land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which c ...

.Crandall-Stotler, B.J., Stotler, R.E., and Long, D.G. 2009. Phylogeny and classification of the Marchantiophyta. Edinburgh Journal of Botany, vol. 66, no. 1, p. 155-198. It is endemic to the

Gulf Coast of the United States The Gulf Coast of the United States, also known as the Gulf South, is the coastline along the Southern United States where they meet the Gulf of Mexico. The coastal states that have a shoreline on the Gulf of Mexico are Texas, Louisiana, Mississ ...

in Arkansas, Louisiana, Mississippi, and Texas. It was first described as the European species '' Petalophyllum ralfsii'' in 1919,Evans, A.W. 1919. Notes on North American Hepaticae - VIII. Bryologist, vol. 22, p. 54-73. but a detailed study later showed that the North American form is a distinct species.Ford, C.H. and Crandall-Stotler, B.J. 2002. Contributions toward a monograph of

Petalophyllum ''Petalophyllum'', or petalwort, is a genus of liverworts in the order Fossombroniales.Crandall-Stotler, B.J., Stotler, R.E., and Long, D.G. 2009. Phylogeny and classification of the Marchantiophyta. Edinburgh Journal of Botany, vo. 66, no. 1, p. ...

( Marchantiophyta). Novon, vol. 12, p. 334-337. ''Petalophyllum americanum'' lives among grasses on sandy, seasonally dry soils of disturbed sites such as pastures, cemeteries, and parks, where it is commonly associated with the liverworts '' Riccia'', ''Fossombronia'', and ''Corsinia''. The plants are

thallose Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms were ...

; that is, the plant is not differentiated into root, stem, and leaf. The thallus is small, typically about 8 mm long by 6.5 mm wide (0.3 in by 0.25 in), and consists of a midrib flanked by two wings that bear leaf-like lamellae on the dorsal surface.

References

{{Taxonbar, from=Q17296322 Fossombroniales