Pneophyllum fragile Kütz.

Scientific Description

Habit and structure. Thallus encrusting, epiphytic and affixed by cell adhesion. Structure pseudoparenchymatous; organisation dorsiventral; construction dimerous, consisting of a single ventral layer of branched filaments composed of non-palisade cells, and unicellular or multicellular simple or branched filaments that arise more or less perpendicularly from cells of ventral layer filaments, each filament composed of cells 5–14 µm in diameter and 3–11 µm long; epithallial cells terminating filaments at the thallus surface, distal walls rounded or flattened but not flared; cells of adjacent filaments joined by cell-fusions, secondary pit-connections absent; trichocytes present or absent, if present, usually occurring singly at thallus surface, not becoming buried within thallus.

Reproduction. Vegetative reproduction unknown. Gametangia, carposporangia, tetrasporangia and bisporangia produced in uniporate conceptacles. Gametangial plants monoecious; carpogonia and spermatangia produced in separate conceptacles. Carpogonia terminating 3-celled filaments arising from the female conceptacle chamber floor. Mature female-carposporangial conceptacle roofs protruding above or flush with surrounding thallus surface, composed of 4–6 cells above the chamber, pores lacking coronas of filaments and flush with surrounding thallus surface, conceptacle chambers 196–218 µm in diameter and 49–150 µm high. Carposporophytes developing within older female conceptacles after karyogamy, when mature composed of a large central fusion cell and with gonimoblast filaments bearing terminal carposporangia. Spermatangial filaments unbranched, arising from the floor of male conceptacle chambers, mature male conceptacle roofs protruding above or flush with surrounding thallus surface, conceptacle chambers 82–109 µm in diameter and 49–91 µm high. Tetrasporangial and bisporangial conceptacle roofs protruding above or flush with surrounding thallus surface, 2–10 cells thick above the chamber, pore canals lined with protruding cells, pores lacking coronas of filaments and flush with surrounding thallus surface, conceptacle chambers 80–265 µm in diameter and 55–195 µm high; tetrasporangia and bisporangia usually peripheral to a central columella, sometimes scattered across the conceptacle chamber floor, each mature sporangium 15–45 µm in diameter and 20–85 µm long, zonately divided.

Distribution.British Isles; Canada; Caribbean; Europe; Mediterranean Sea; Pacific Mexico; subtropical and tropical W. Aust.; USA; USSR. In southern Australia, Bunbury, W. Aust., eastwards to Sealers Cove, Wilsons Promontory., Vic., and around Tas.

Habitat. P. fragile occurs commonly on Acrocarpia spp., Laurencia spp., and on the seagrass Amphibolis antarctica.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 269–271 (1996)]