The liverwort genera (Bryophyta: Hepaticae and Anthocerotae) of Britain and Ireland

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L. Watson and M. J. Dallwitz

Pleurocladula Grolle

Including Pleuroclada.

Gametophyte. Plants leafy (whitish-green and becoming white on drying, in patches, tufts or growing through other bryophytes). With procumbent to erect shoots, and the occasional sub-pinnate branching lateral. The branching apical, or lateral (rarely, then intercalary); not dichotomous. The stems with cortical cells clearly differentiated from the cells of the central strand (the cortical cells large and hyaline); translucent. Plants with neither flagella nor flagelliform shoots or branches. Acrogynous. The leaf cells without trigones; smooth, not mamillose. Rhizoids present; colourless.

The leafy shoots dorsiventral, with two equal ranks of lateral leaves and a third, ventral rank of smaller underleaves; not julaceous. The vegetative leaves more or less symmetrical to markedly asymmetrical. The vegetative leaves more or less transversely inserted, or transversely inserted to obliquely inserted; alternate; overlapping, or overlapping to distant (approximate to subimbricate); succubous (if determinable). The leaf margins entire; deflexed (at least, the leaves very concave); not or only slightly dorsally decurrent. The vegetative leaves more or less orbicular and very concave, symmetrically to asymmetrically about 1/3 to 1/2 bilobed (the lobes incurved, broadly triangular, acute); not complicate-bilobed; leaves not keeled; without vittae. Underleaves smaller than the laterals though well developed and conspicuous (0.3–0.5 mm long and somewhat smaller than the laterals, but quite large, ovate-lanceolate to ovate, entire or with a single tooth or lobe on one or both sides); bilobed (but not apically so), or not bilobed. The cells of the gametophyte with numerous small chloroplasts. The chloroplast-containing cells without oil bodies. Gemmae rare (in globose clusters at shoot apices, surrounded by 1–2 circles of reatively large leaves and underleaves, spherical to ellipsoid and unicellular).

The plants dioecious.

Male inflorescences comprising 2–8(-20) distant to imbricate pairs of bracts. Male bracts subtending a single antheridium, or a single antheridium to 2 antheridia. Marsupia absent. Female bracts present. Female bracts much larger than the (upper) leaves (basally free or connate, inrolled, sometimes bi- or occasionally tri-lobed to about 1/3, then the lobes broadly triangular and acute). Bracteole present (smaller than or similar in size to the bracts, narrowly oblong and sub-dentate). Perianth present (but undeveloped in the absence of fertilization); long-exserted, basally fleshy, subclavate-cylindrical, trigonous above, contracted at the weakly lobed and crenulate-denticulate mouth. Perianth distally smooth, not plicate. Perianth not beaked.

Sporophyte. The sporophyte elevated by elongation of the seta, with no intercalary meristem. The capsule ovoid to shortly cylindrical (ellipsoid). The capsule wall 2 layered (the inner layer with semi-annular thickenings). The spores unicellular when shed. Elaters present; bispirally thickened; free (?). Ecology. In wet places; occurring in acid conditions; montane. In peaty or gravelly soil at high elevations, irrigated by melt-water.

British representation. 1 species (P. albescens); Scotland.

Classification. Class/Division Hepaticae. Subclass/Class Jungermanniidae. Order Jungermanniales. Family Cephaloziaceae.

Illustrations. • P. albescens: Jameson, in Macvicar (1926). • P. albescens (as Pleuroclada): Pearson fig. LXXV (1902). • P. albescens: Pearson fig. LXXV legend. • P. albescens var. islandica: Pearson fig. LXXVI (1902). • P. albescens var. islandica: Pearson fig. LXXVI legend.

To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2005 onwards. The liverwort genera (Bryophyta: Hepaticae and Anthocerotae) of Britain and Ireland. Version: 24th February 2016.’.