BFNA Title: Pleurocladula
Author: David M. Krayesky and Jerry G. Chmielewski
Date: May 14, 2016
Edit Level: R
Version: 1

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden
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XX.  PLEUROCLADULA Grolle, J. Bryol. 10: 269.  1979 * [Greek pleuro side, Greek clado branch; alluding to lateral branching]


David M. Krayesky

Jerry G. Chmielewski

Pleurocladula º Pleuroclada Spruce 1882 (nom. illeg.), non Pleurocladia A. Braun 1855


Plants light pellucid green, in full sun or shade, nearly white when dry (occasionally reddish brown).  Stem possessing a hyalodermis; Frullania type (lateral-terminal) branching common and lateral-intercalary branching rare; flagelliform branches occurring in some populations.  Leaves transverse-succubous, not decurrent, distant to imbricate, entire; 2-lobed, lobes triangular, and concave; oil bodies absent.  Underleaves large, nearly as long as leaves but only half as wide, often possessing 1--2 sub-basal teeth.  Specialized asexual reproduction by gemmae uncommon, 1-celled, spherical to ellipsoidal, at shoot apex.  Sexual condition dioicous.  Androecia intercalary, each bract with basal antical tooth; antheridia occurring singly per bract, ovoid, with non-tiered jacket cells and a 2-seriate stalk.  Gynoecia terminal, bracteole always narrower and sometimes shorter than bracts; perianth clavate to oblong or fusiform, fleshy and multistratose at base, mouth lobate with a crenulate margin.  Sporophyte seta yielding 8--12 epidermal and 5--8 inner cell rows; capsule ellipsoidal, four valved, capsule wall 2-stratose. 


Species 1 (1 in the flora): North America, Europe and Asia.


Pleurocladula albescens (Hooker) Grolle and P. islandica (Nees) Grolle have been treated as separate species (e.g. M. Krzakowa and J. Sweykowski 1981; R. Grolle 1983).  We concur with J. A. Paton’s (1999) assessment that the genus is monotypic as Paton (1976) provided ample evidence for the inclusion of P. islandica into synonymy with P. albescens. 


The status of Pleurocladula is a point of debate.  A. A. Vilnet et al. (2012) proposed that Cephalozia is polyphyletic forming two clades.  One Cephalozia clade included the generitype, as well as other Cephalozia species.  The second clade included species of Cephalozia, Pleurocladula, and Schofieldia.  J. Váňa et al. (2013) have transferred those species in the second clade to Fuscocepaloziopsis.  K. Feldberg et al. (2016) concur with Váňa et al. (2013).  Although the Feldberg et al. (2016) analysis of the Cephaloziaceae is the most comprehensive molecular assessment of the group to date, the maximum likelihood value of the Fuscocepaloziopsis clade does not provide the same level of support as evidenced in the recent treatment of Odontoschisma (S. C. Aranda et al. 2014).  For this reason we continue to recognize Pleurocladula, Schofieldia, and Cephalozia sensu lato as distinct genera.  In order to support the reorganization of these specific Cephaloziaceae taxa into two genera, namely, Cephalozia and Fuscocephaloziopsis, both an extensive anatomical study and a molecular evaluation with a very strong level of support will need to be demonstrated, as is the case with the recent treatments of Odontoschisma (S. C. Aranda et al. 2014; S. R. Gradstein and A. L. Ilkiu-Borges 2015). 


SELECTED REFERENCES  Aranda, S.C., S.R. Gradstein, J. Patiňo, B. Laenen, A. Désamoré, and A. Vanderpoorten.  2014.  Crandall-Stotler, B., R.E. Stotler, and D.G. Long.  2009.  Phylogeny and classification of the Marchantiophyta.  Edinburgh J. Bot. 66: 155--198.  Feldberg, K., J. Váňa, J. Krusche, J. Kretschmann, S. D. F. Patzak, O. A. Pérez-Escobar, N. R. Rudolf, N. Seefelder, A. Schäfer-Verwimp, D. G. Long, H. Schneider, and J. Heinrichs.  2016.  A phylogeny of Cephaloziaceae (Jungermanniopsida) based on nuclear and chloroplast DNA markers.  Organisms Diversity and Evolution 16 [doi: 10.1007/s13127-016-0284-4].  Frye, T. C. and L. Clark.  1943.  Hepaticae of North America.  Univ. Washington Publ. Biol. 6(2): 187--190.  Geissler, P. and H. Bischler.  1989.  Index Hepaticarum: Vol. 11 Naiadea to Pycnoscenus,  J. Cramer, Berlin, Germany.  Gradstein, S. R. and A. L. Ilkiu-Borges.  2015.  A taxonomic monograph of the genus Odontoschisma.  Nova Hedwigia 100: 16--100.  Grolle, R.  1979.  Miscellanea hepaticologica 171--180.  J. Bryol. 10: 263--272.  Grolle, R.  1983.  Hepatics of Europe including the Azores: An annotated list of species, with synonyms from the recent literature.  J. Bryol. 12: 403--459.  Hooker, W. J.  1816.  British Jungermanniae.  84 plates and 4 supplementary plates.  London.  Krzakowa, M. and J. Szweykowski.  1981.  A species concept in the genus Pleurocladula (Hepaticae).  Acta Soc. Botanic. Poloniae 39: 465--479.  Paton, J. A.  1976.  Pleuroclada albescens (Hook.) Spruce with gemmae.  J. Bryol. 9: 1--5.  Paton, J. A.  1999.  The Liverwort Flora of the British Isles.  Harley Books, Colchester, England.  Schuster, R. M.  1974.  Pleurocladula.  In:  R. M. Schuster.  The Hepaticae and Anthocerotae of North America east of the hundredth meridian. New York, Vol. 3, Pp. 66-6-671.  Smith, A. J. E.  1990.  The Liverworts of Britain and Ireland.  Cambridge University Press.  Cambridge, UK.  Spruce, R.  1882.  Pleuroclada.  In: R. Spruce.  On Cephalozia, its subgenera and some allied genera. Malton, pp. 77--80, Malton.  Váňa, J., L. Söderström, A. Hagborg,  and M. von Konrat.  2013.  Notes on early plants today. 41. New combinations and synonyms in Cephaloziaceae (Marchantiophyta).  Phytotaxa 112: 7--15.  Vilnet, A. A., N. A. Konstantinova, and A. V. Troitsky.  2012.  Molecular phylogeny and systematics of the suborder Cephaloziineae with special attention to the family Cephaloziaceae s.l. (Jungermanniales, Marchantiophyta).  Arctoa 21: 113--132.


1. Pleurocladula albescens (Hooker) Grolle, J. Bryol. 10: 269.  1979


Jungermannia albescens Hooker, Brit. Jungermann., pl. 72 and suppl. pl. 4.  1815; Pleurocladula islandica (Nees) Grolle


Plants ca. 4.7--9.4 x 0.2--0.5 mm; prostrate to gregarious, growing in mats, turfs, or singly among other bryophytes.  Stems fleshy 120--185 \um, cortical cells thin walled and 23--39 x 24--39 µm; medullary cells thick walled and 18--24 x 18--22 \um, medulla 112--123 µm in diameter and 5--8 stratose; flagelliform branches occurring in some populations.  Leaves distant to imbricate; erecto-patent; concave; suborbicular 240--397 µm long x 200--400 µm broad; margins entire; 2-lobed, lobes triangular, incurved; sinus 1/3--1/2 the length of the leaf, base of sinus rounded to acute; marginal cells 17--31 x 17--31 \um; median cells in lobes 17--26 x 17--35 µm; median leaf cells 17--29 x 23--32 \um; basal cells 23--39 x 23--36 µm. Oil-bodies absent.  Rhizoids scarce to abundant, and abundant on flagelliform branches, colorless.  Underleaves large 273--307 x 99--177 \um; erecto-patent; ovate to sublanceolate; apices acute to obtuse; with or without basal teeth, often present on one side, occasionally on both.  Specialized asexual reproduction by gemmae 23--26 \um in diameter.  Androecia bracts 0.5--0.6 x 0.4--0.5 mm; in 15--18 pairs; 2-lobed, and with basal antical tooth.  Gynoecia bracts 1--1.3 x 0.9--1.2 mm and bracteoles 0.5--0.6 x 0.4--0.5 mm; in series of 2; bracts 2-lobed, and much larger than the leaves; bracteoles free or connate to the base of the bract, unlobed or shallowly 2-lobed with 1--3 teeth.  Perianth 1.9--2.9 x 0.8--0.9 mm; clavate to oblong or fusiform; fleshy and multistratose at base; mouth lobate with a crenulate margin.  Seta 250--322 µm in diameter.  Capsule 1.1--1.5 x 0.4--0.5 mm, capsule wall 2 cell layers thick; epidermal cells 15--38 x 22--40 \um; interior cells 15--20 x 19--76 \um in diameter.  Elaters 7--10 µm in diameter, 127--318 µm in length, and (1--)2-spiraled.  Spores brown, vermiculate-verrucose 14--16 \um . 



Northern Hemisphere Arctic and temperate (alpine to montane) areas, on fine to gravelly soils, peaty soils, and rock, and on the banks of small streams and ephemeral ponds associated with peatland areas; low to high elevations; Greenland; Alta., B.C., Nfld. and Labr., N.W.T., Nunavut, Que., Yukon; Alaska, Calif., Mont., Wash.; Europe; Asia. 


R. M. Schuster (1995) indicated Pleurocladula albescens has a tendency toward being acidophilic. There are some doubtful records in the United States and these published records will be treated here as erroneous.  These aforementioned records include: the Wolf and Hall (1878) report from Illinois and the Watson s.n. 1972 collection in TROPICOS at MO from New Hampshire.  The Wolf and Hall (1878) report was treated by Schuster (1974) as an erroneous, as we have been unable to locate this collection we continue to follow the Schuster (1974) assessment of this population.  The Watson s.n. 1972 collection from New Hampshire is not Pleurocladula albescens, but is Orthocaulis kunzeanus (Huebener) H. Buch.