BFNA Title: Petalophyllaceae
XX. PETALOPHYLLACEAE Stotler & Crand.-Stotl.
Barbara J. Crandall-Stotler
Plants thallose, simple or once furcate, light green to light yellow green, growing solitary or in small [large] patches. Thallus wings flattened to erect, fan-shaped, multistratose at the base, becoming unistratose at the margin, with [without] erect dorsal lamellae; midrib fleshy, dorsally compressed (concave), with a ventral mycorrhizal zone; central strand absent; ventral surface with 2 rows of small scales; rhizoids hyaline. Asexual reproduction by perennating apical tubers. Dioicous, heterothallic [homothallic], gametangia dorsal on thallus midrib; antheridia dispersed [clustered], subtended by lamellar extensions, or [interspersed with small bracts]; archegonia clustered, mixed with paraphyses, surrounded by a pseudoperianth. Sporophytes enclosed in a thin shoot calyptra and enlarged pseudoperianth; capsules spheroidal, nonvalvate, dehiscence irregular; capsule walls 3--4-stratose, with secondary thickenings in all layers.
Genera 2 (1 in the flora): Known from North America, w Europe, n Africa, India, New Zealand, and w Australia.
Petalophyllaceae was segregated from the Fossombroniaceae on the basis of the following characters that differentiate Petalophyllum (and Sewardiella) from Fossombronia: undissected, thallose gametophyte; clustered archegonia, surrounded by a pseudoperianth; capsule walls 3--4-stratose throughout; secondary cell wall thickenings in all capsule wall layers. Molecular phylogenetic studies further support its segregation from the Fossombroniaceae (B. J. Crandall-Stotler et al. 2005).
Selected References: Crandall-Stotler, B. J., R. E. Stotler and C. H. Ford. 2002. Contributions towards a monograph of Petalophyllum (Marchantiophyta). Novon 12: 334--337. Crandall-Stotler, B. J., L. L. Forrest and R. E. Stotler. 2005. Evolutionary trends in the simple thalloid liverworts (Marchantiophyta, Jungermanniopsida subclass Metzgeriidae). Taxon 54: 299--316.
1. PETALOPHYLLUM Nees & Gottsche ex Lehmann, Nov. Stirp. Pugillus 8: 29. 1844 [Greek, petalos, broad, and phyllo, leaf]
Plants large, to 11.2 mm x 9 mm. Wings with obliquely oriented, dorsal lamellae; wing margin entire or highly erose, with or without marginal cells distinct; cells thin-walled, without trigones; oil bodies small, spheroidal, homogeneous, 40--75 per cell. Lamellae leaf-like, extending from the costa to near the wing margin, mostly 1-stratose, multistratose at the base, with the margins entire, plane, undulate, or sinuate. Heterothallic, male plants smaller than female. Antheridia arranged in 1--5 rows near the thallus apex, individually subtended by lobed extensions of the lamellae, yellow at maturity, stalk 4-seriate. Gynoecia 1--3 per thallus; pseudoperianths cylindric to broadly companulate, the outer surface with or without wing-like, lamellar outgrowths, the inner surface smooth; the mouth erect to incurved or recurved, subentire, coarsely toothed or highly lacerate, with or without 1-seriate cilia. Spores large, spheroidal, light to dark reddish brown, areolate on both proximal and distal faces, with a central, proximal depression.
Species 5 (1 in the flora): best known from seasonally dry habitats in North America, w Europe, n Africa, India, New Zealand, w Australia.
1. Petalophyllum americanum C. H. Ford & Crand.-Stotl., Novon 12: 335. 2002 E
Plants 4--8 mm x 2.5--6.5 mm, in small, scattered patches on exposed, sandy soil, often among grasses. Wings flattened to suberect, with the margins entire, plane to slightly undulate; median cells elongate, 50--80 /um x 40--52 /um; marginal cells smaller, quadrate or tangentially elongate, 36--40 /um x 34--44 /um; lamellae with the margins plane to slightly undulate, never sinuate; ventral scales subulate, 120--160 /um x 45--60 /um, 2(--3) cells wide at the base, with 1--3 short marginal cilia, terminated by slime papillae. Male plants 2.5--3.2 mm wide; thallus wings suberect; antheridia in 2--3 irregular rows. Gynoecia 1(--2) per thallus, with 5--9 archegonia per gynoecium; pseudoperianths campanulate, 1.5--3.1 mm x 1.9--4.3 mm, with 1(--2) lengthwise slits on the acroscopic side, laterally confluent with the wing lamellae; outer surface with vertical wing-like lamellae 2--5 cells high; the mouth erect to incurved, sinuate, subentire to coarsely dentate, never ciliate. Sporophytes 1(--2) in each pseudoperianth. Capsules dark brown to black, 1.4--2.3 mm; outer cells quadrate, with reddish brown, nodular, I-type thickenings on all radial walls; inner cell layers with reddish brown semiannular thickenings. Spores 48--60 /um. Elaters 240--300 x 12--16 /um, occasionally branched, with 3--4(--5) reddish brown spiral thickening bands, becoming 2-spiraled at the ends.
Capsules mature Feb. to March; found among grasses on sandy, seasonally dry soils of disturbed sites such as pastures, cemeteries and parks, often associated with Fossombronia, Corsinia, and Riccia; North American endemic of the Gulf Coastal Plain and Interior Highlands; low to moderate elevations; Ark., La., Miss., Tex.
A. W. Evans (1919) first reported Petalophyllum for North America, based on his study of two collections from Texas. These initial specimens were referred to P. ralfsii, a well-known species of the British Isles and Mediterranean region, an application that persisted in subsequent North American treatments of the genus, including that of R. M. Schuster (1992). A detailed morphological comparison of North American specimens with the type and numerous collections of European P. ralfsii by B. J. Crandall-Stotler et al. (2002), however, provided convincing evidence that the North American plants are a distinct species, which was named P. americanum. Major distinguishing characters of this North American endemic are as follows: (1) thalli typically smaller than those of P. ralfsii, (2) wings and lamellar margins plane to slightly undulate, compared to sinuate in P. ralfsii, (3) pseudoperianth mouth subentire to coarsely toothed, compared to laciniate with uniseriate cilia in P. ralfsii, (4) elaters 3--4(--5)-spiraled compared to 2--3-spiraled in P. ralfsii. The thalli of P. americanum are present only from January through March, forming subterranean apical tubers soon after antheridial and sporophyte maturation. Following tuber formation, the thallus dies, and the plant persists as either spores or tubers in the soil bank.
SELECTED REFERENCES Bloomquist, H. L. 1939. Notes on Southern Hepaticae. Bryologist 42: 31--32. Crandall-Stotler, B. J., R. E. Stotler, and C. H. Ford. 2002. Contributions toward a monograph of Petalophyllum (Marchantiophyta). Novon 12: 334--337. Evans, A. W. 1919. Notes on North American Hepaticae---VIII. Bryologist 22: 54--73. Kyzer, J. W. and D. L. Marsh. 1999. Occurrences of Petalophyllum (Fossombroniaceae) in the Interior Highlands of Arkansas. J. Arkansas Acad. Sci. 53: 145--146. Schuster, R. M. 1992. The Hepaticae and Anthocerotae of North America, Vol. V. Field Museum, Chicago.