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

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L. Watson and M. J. Dallwitz

Plagiochila (Dum.) Dum.

Gametophyte. Plants very small to robust, leafy. In intricate mats or turfs, the mats often pendent, with leafy shoots arising from rhizoid-covered rhizomatous stems, sparsely to freely branched from the postical leaf angles, innovating from below the perianth. Plants often with flagella or flagelliform shoots or branches. Acrogynous. The leaf cells with trigones (small to large and bulging). Rhizoids present (but more or less confined to the flagella and basal axes, the leafy shoots with few or none).

The leafy shoots dorsiventral, with two equal ranks of lateral leaves and a third, ventral rank of smaller underleaves, or dorsiventral, with the two ranks of laterals more or less equal in size and the ventral rank lacking. The vegetative leaves more or less markedly asymmetrical (usually convex, often varying in size and shape along the stems). The vegetative leaves obliquely inserted; alternate; overlapping; succubous. The leaf margins at least ventrally toothed; dorsally flat to deflexed; dorsally decurrent (sometimes decurrent on both sides), or not or only slightly dorsally decurrent. The vegetative leaves undivided, or bilobed, or several-lobed (the apices rounded or truncate, toothed, or only rarely deeply bilobed); not complicate-bilobed; with vittae, or without vittae. Underleaves present but much reduced or vestigial (limited to new growth, small and usually subulate), or absent; not bilobed. The cells of the gametophyte with numerous small chloroplasts. The chloroplast-containing cells with conspicuous oil bodies (4–15 per cell). Gemmae absent (but propagating vegetatively by caducous leaves and assorted fragments).

The plants dioecious.

Male inflorescences terminal or intercalary, with closely imbricate, basally saccate bracts smaller than the leaves. Male bracts subtending 2 antheridia (usually), or several antheridia (someimes up to ten). Female inflorescences terminating stems or branches. Marsupia absent. Female bracts present (usually two, similar to the leaves but with more numerous and coarser teeth). Bracteole present, or absent (usually). Perianth present; campanulate to cylindrical, strongly laterally compressed, often ventrally keeled and sometimes dorsally and/or ventrally winged, the wide mouth truncate or rotundate, dentate or ciliate. Perianth distally smooth, not plicate. Perianth not beaked. Calyptra present and well developed (free).

Sporophyte. The sporophyte elevated by elongation of the seta, with no intercalary meristem. The capsule usually shortly pedicellate, globose to ovoid. The capsule wall 4–10 layered. The spores unicellular when shed. Elaters present; bispirally thickened; free.

British representation. 9 species; England, Wales, Scotland, and Ireland.

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

Illustrations. • cf. P. asplenoides: Jameson, in Macvicar (1926). • P. asplenoides: Pearson fig. 111 (1902). • P. asplenoides: Pearson fig. 111 legend. • P. asplenoides: Pearson fig. 113 (1902). • P. asplenoides: Pearson fig. 113 legend. • P. asplenoides var. minor (as P. dillenii): Pearson fig. 114 (1902). • P. asplenoides var. minor (as P. dillenii): Pearson fig. 114 legend. • cf. P. atlantica: Jameson, in Macvicar (1926). • P. atlantica (as P. ambiguosa): Pearson fig. 115 (1902). • P. atlantica (as P. ambiguosa): Pearson fig. 115 legend. • P. carringtonii (as Jamesoniella): Jameson, in Macvicar (1926). • P. carringtonii (as Jamesoniella): Pearson fig. CXXI (1902). • P. carringtonii (as Jamesoniella): Pearson fig. CXXI legend. • cf. P. exigua (as P. tridenticulata): Jameson, in Macvicar (1926). • P. exigua: Peason fig. 119 (1902). • P. exigua: Peason fig. 119 legend. • cf. P. exigua (as P. ‘trideniculata’): Peason fig. 118 (1902). • legCXVIII.jpg<@subject. • cf.. • P.. • exigua. • (as. • P.. • ‘trideniculata’):. • Peason. • fig.. • 118. • legend>. • cf. P. exigua (as P. stableri): Jameson, in Macvicar (1926). • cf. P. exigua (as P. stableri): Pearson fig. CXII (1902). • cf. P. exigua (as P. stableri): Pearson fig. CXII legend. • P. killarniensis: Jameson, in Macvicar (1926). • P. punctata: Jameson, in Macvicar (1926). • P. punctata: Pearson fig. CXVII (1902). • P. punctata: Pearson fig. CXVII legend. • P. spinulosa: Jameson, in Macvicar (1926). • P. spinulosa: Pearson fig. CXVI (1902). • P. spinulosa: Pearson fig. CXVI 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.’.