Pallaviciniaceae is a widely-distributed family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of liverworts

Marchantiophyta

The Marchantiophyta are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information....

 in the order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Metzgeriales

Metzgeriales

Metzgeriales is an order of liverworts. The group is sometimes called the simple thalloid liverworts: "thalloid" because the members lack structures resembling stems or leaves, and "simple" because their tissues are thin and relatively undifferentiated. All species in the order have a small...

. All species are thallose

Thallus (tissue)

Thallus, from Latinized Greek θαλλός , meaning a green shoot or twig, is the undifferentiated vegetative tissue of some organisms in diverse groups such as algae, fungus, some liverworts, lichens, and the Myxogastria. Many of these organisms were previously known as the thallophytes, a polyphyletic...

, typically organized as a thick central costa

Costa

Costa may refer to:* Costa , including origin of the name and people sharing the surname* Costa, scientific term, from Latin costa "rib" ** In botany, the central strand of a bryophyte leaf or thallus...

 (midvein), each side with a broad wing of tissue one cell in thickness. All species are dioicous

Monoicous

Monoicous is a botanical term used to describe plants which bear both sperm and eggs on the same gametophyte. Dioicous is the complementary term describing species in which gametophytes produce only sperm or eggs but never both. The terms are used largely but not exclusively in the context of...

. The greatest diversity is in Australasia

Australasia

Australasia is a region of Oceania comprising Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. The term was coined by Charles de Brosses in Histoire des navigations aux terres australes...

, with some species endemic to that region, though species belonging to the family may be found on every continent except Antarctica.