BFNA Title: Pallavicinia
Plants 15--60 mm x 2--8 mm, translucent-green to deep green, without other pigments, with only old portion of thalli becoming brownish green or decolorate. Thallus branching latero-ventral, rarely furcate, thallus flattened, margin plane or lightly undulate, with well-defined biconvex costa, mostly with clearly visible (whitish or yellowish brownish) single median vascular strand; shoot apices ventrally with 2--3--celled slime papillae. Rhizoids brownish, distributed along ventral surface of costa. Thallus margin entire (except for mostly ephemeral 1(--3)-celled teeth or slime papillae) [dentate]. Thallus lamina 1 cell in thickness, laminar cells thin-walled, polygonal; along margin dentate-ciliate to virtually entire. Asexual reproduction absent. Sexual condition dioicous. Androecia dorsal; antheridia in one row on each side of midrib [irregularly scattered over midrib], each subtended by a laciniate-dentate scale. Gynoecia solitary on dorsal side of costa, outer involucre of complete ring of laciniform scales, free or united proximally; capsule surrounded by a tubular pseudoperianth. Seta 17--24 mm. Capsule wall 2-stratose. Spores 17--24 \um, areolate to papillose. Elaters ca. 150--350 x 7--9 \um, 2(--3)-spiral.
ca. 30 (1 in the flora): North America, Central America, South America,
SELECTED REFERENCE Doyle W.T. and R.E. Stotler. 2006 Contribution toward a bryoflora of California III. Keys and Annotated species Catalogue for Liverworts and Hornworts. Madroño. 53: 89--197.
1. Pallavicinia lyellii (Hooker) Gray,
Plants 15--50 x 2--6 mm. Thallus with lightly undulate margin, with clearly visible (whitish or yellowish brownish) single median vascular strand. Thallus margin mostly entire except for regularly spaced ephemeral 1(--3)-celled teeth or slime papillae (quickly disintegrating in herbarium or in old portions of thallus). Thallus lamina with cells thin-walled, 35--100 x 24--48 \um, cells slightly elongated along margin. Oil-bodies small and numerous, in middle part of lamina 30--65 per cell, spherical to ellipsoidal, fusiform, botryoidal to granulate, small 2--6 x 2--4 \um to larger 8--11 x 2--5 \um. Androecia with antheridia and scales in one row on each side of midrib; antheridial body spherical to shortly ellipsoidal. Gynoecia with outer involucre 1.5--2 \um high in maturity, consisting of ciliate-laciniate segments; inner involucre (pseudoperianth) tubular, 5--8 mm high, ciliate-laciniate at mouth. Seta 17--24 mm. Spores 17--24 \um, areolate. Elaters 2--3-spiral.
Wet and shady places along banks of ponds, stream, lakes, or in swamps associated with flowing water, only in acidic habitats; low to moderate elevations; N.B., Nfld. and Labr. (Nfld.), N.S., Ont.; Ala., Ark., Calif., Conn., D.C., Fla., Ga., Ill., Ind., Ky., La., Maine, Md., Mass., Mich., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Tex., Vt., Va., W.Va.; Central America: South America; Eurasia: Africa; Pacific Islands; Australia.