XX. PLEUROZIACEAE Müll. Frib
Barbara M. Thiers
Plants forming thick mats or wefts or spreading from substrate, rhizomatous branch system present; branches from axils of leaves; without flagella. Leaves alternate, succubous, deeply concave, 2-lobed, the lobes sharply folded together and usually strongly dimorphic; underleaves absent. Rhizoids restricted to stem bases. Specialized asexual reproduction absent. Androecia on short branches, 1 antheridium per bract. Gynoecium terminal on a short branch, subtended by a single bract. Perianth without subfloral branches, well developed, ovoid, narrowed to mouth, plicate, perigynium absent. Sporophytes robust. Seta short, composed of numerous cell rows with no detectable pattern of layering. Capsule subspherical to ovoid, wall 6--8 cell layers thick, outermost cells with nodular thickenings along adjacent cell walls; innermost cell layer covered with fenestrate secondary thickenings; valves straight, divided to base. Elaters 2-spiral, brown. Spores covered with crowded spines.
Genera 1, species 11 (1 species in the flora): Canada; Central America; South America; Eurasia; Africa; Atlantic Islands (including Macaronesia); Indian Ocean Islands; Pacific Islands (including Hawaii and New Zealand); Australia.
Pleuroziaceae is the sole member of the Pleuroziales Schljakov, and phylogenetically is quite isolated from other hepatics. Although characterized by well-differentiated stems and leaves, Pleuroziales are placed in the Metzgeriidae based on molecular data, as sister group to the rest of the simple thalloid hepatics (Crandall-Stotler et al. 2000, 2009).
1. PLEUROZIA Dumortier, Recueil Observ. Jungerm. 15. 1835 * [Greek pleuron or rib, sharply folded lateral leaves give ribbed appearance]
Barbara M. Thiers
Plants wine-red. Stem epidermis 1--4 cell rows wide, cortex 8--15 cells wide. Leaves when entire broadly ovate to orbicular, apex rounded, margins entire, base rounded to cordate; bilobed leaves with ventral lobes ovate to orbicular, concave, margins entire to undulate and/or dentate near apex, apex entire, irregularly dentate or shallowly 2-lobed; dorsal lobules tubular, opening restricted to an aperture complex positioned on adaxial surface near apex or mid portion of lobule, access to lobule interior controlled by a hinged, spathulate valve that fits into a concave abutment, valve and abutment oriented toward lobule base, situated in a weakly to well-defined oblong or circular basin bordered or overarched by a rounded lip; lobule attached to lobe for 0.3 or less of lobule length. Oil bodies colorless, granular, 18--28 per cell. Androecia bracts in 4--10 pairs. Gynoecial bract 3-lobed, obdeltoid, lobes triangular; perianth mouth ciliate, cilia of 3--10 cells, sometimes articulate or branched. Spores 25--50 µm diam., spherical, golden brown.
Species 11, 1 in the flora: Canada; Central America; South America; Eurasia; Africa; Atlantic Islands (including Macaronesia); Indian Ocean Islands; Pacific Islands (including Hawaii and New Zealand); Australia.
SELECTED REFERENCES Crandall-Stotler et al., 2000. Morphology and classification of the Marchantiophyta. In: Shaw, A. J. & B. Goffinet. (eds). Bryophyte Biology, pp. 21--70.Cambridge: Cambridge University Press. Schuster, R. M. 1965. Studies on Hepaticae. XVI. The morphology and systematic position of the suborder Pleuroziinae. Transactions of the British Bryological Society 4: 794-800. Thiers, B. M. 1992. A monograph of Pleurozia (Hepaticae: Pleuroziaceae). Bryologist 96: 517--554. Wang, B. J. et al., 2009. The complete mitochondrial genome sequence of the liverwort Pleurozia purpurea reveals extremely conservative mitochondrial genome evolution in liverworts. Current Genetics 55: 601--609.
1. Pleurozia purpurea Lindb., Acta Soc. Fauna Fl. Fenn. 1 (2): 27. 1877
Plants to 8 cm long, 2--3.5 mm wide; elongate stems sparsely branched. Leaves when entire restricted to branch bases, 0.2--0.3 x 0.1 mm, margins short-ciliate near apex; saccate-lobuled leaves dominant on all stems; ventral lobes 2--3 x 1.5--3.5 mm, strongly concave, apex 2-fid to ca. 0.2 leaf length, margins coarsely dentate at apex; cells of leaf apex quadrate, 25--50 x 25--38 \um, cells at midleaf quadrate to rectangular, 25--40 x 25--38 \um, cells of leaf base rectangular, 50--88 x 25--30 µm; dorsal lobules ovoid to deltoid, curved somewhat toward stem, 1--2 x 1--2 mm, attachment to ventral lobe extending 0.5--0.75 \um, aperture at mid length of lobule, situated in an oblong basin oblong, lip present on proximal border of basin, only slightly overarching it. Sexual condition dioicous. Androecia bracts spathulate. Gynoecia when fertile lacking innovations, bracts 2--3 x 2.5--3 mm, lobes extending 0.20 bract length or less, apices acutely rounded, margins dentate. Perianth plicate in distal half, apical cilia short, with frequent articulations.
Terrestrial in bogs or other wet habitats in coastal areas; B.C., Alaska; Europe (Britain, Norway and Denmark); Asia (Bhutan, India, Nepal).
Pleurozia purpurea was placed by B. M. Thiers (1992) in subgenus Constantifolia. If examined only superficially, P. purpurea might be confused with members of the Jungermanniaceae such as Anastrophyllum or Jamesoniella, which also has reddish secondary pigmentation and plicate perianths. However, Pleurozia purpurea is a much larger plant, and the structure of the bilobed leaves, with saccate dorsal lobes, is like no other species in North America. The distichous leaf arrangement, absence of underleaves, and the single gynoecial bract surrounding the gynoecium are also diagnostic.