Ricciaceae

Terrestrial or free-floating aquatic, monoicous or dioicous. Specialised asexual propagules absent. Plant a simple to repetitively forked thallus, often radiating out from a central point to form a circular or semi-circular outline; thallus with narrow to broad grooves adaxially along midline, divided into photosynthetic tissue layer and a thinner storage tissue layer, entire, glabrous or hairy along margin and rarely on adaxial surface; photosynthetic tissue divided into 2–4 tiers of air chambers, sometimes defined by pentagonal boundaries on adaxial surface, separated by unistratose walls, with simple air pores sometimes enlarging with age to become cavernous, or with narrow air columns bounded by closely packed vertical rows of photosynthetic tissue; air chambers without photosynthetic filaments; adaxial epidermal cells polygonal, thin- or thick- (not in Victoria) walled; abaxial storage tissue rudimentary to thick, rarely inverted and adaxial to photosynthetic tissue (not in Victoria); oil cells absent or present in dorsal epidermis, storage tissue and abaxial scales; thallus margins entire, sometimes ciliate. Abaxial scales in 1, 2 or several rows, without appendages or with small appendages, sometimes inconspicuous, usually hyaline, sometimes purplish. Rhizoids sometimes absent when aquatic, otherwise present, without and with internal peg-like thickenings. Antheridia embedded along adaxial thallus midline. Sporophytes embedded along adaxial thallus midline; involucres absent; pseudoperianth absent. Seta and foot absent. Capsules globose, cleistocarpous, unistratose; elaters absent. Spores tetrahedral to globular with a convex distal face and a proximal face with or without a triradiate ridge, areolate and often raised in corners to form tuberculate or papillate extensions or rarely smooth, usually with less pronounced ornamentation on proximal face, black, brown, reddish brown or purplish brown, shed singly or rarely in tetrads (not in Victoria).