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

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L. Watson and M. J. Dallwitz

Pleurozia Dum.

Gametophyte. Plants robust, reddish-yellow to reddish- or deep purple, leafy. The shoots ascending from a rhizomatous base, simple or with 2–3 branches, ventrally secund distally, the inflorescences on short lateral branches. The branching conventional. Acrogynous. The leaf cells with trigones (these very large). Rhizoids present only in the rhizomatous base.

The leafy shoots dorsiventral, with the two ranks of laterals more or less equal in size and the ventral rank lacking. The vegetative leaves transversely inserted to obliquely inserted (?); alternate; overlapping (closely imbricate and concealing the stem, ventrally secund); incubous; bilobed (almost to the base, conduplicate, the dorsal lobe lobe broadly ovate and widely crossing the stem, convex, apically emerginate and dentate, its dorsal margin almost semi-circular with 2–3 teeth near the base, the ventral lobe much smaller, pyriform to ovoid and uniquely, complexly modified to hold water, being saccate via two internal flaps and folding); complicate-bilobed. The ventral lobes much smaller than the dorsal ones. The vegetative leaves without vittae. The cells of the gametophyte with numerous small chloroplasts. Gemmae absent.

The plants bisexual; having the gametangia grouped into bracteate inflorescences; autoecious.

Male inflorescences on short lateral branches near the female one, spicate with 6–12 pairs of imbricate, broadly ovate-rotundate, complicate-concave bracts with apices entire to as much as 1/3 3–4 lobed. Male bracts subtending a single antheridium (ovoid-globose). Female inflorescences lateral, on a short branch near the main stem apex. Female bracts present (with the antical lobe narrower than in the leaves, the postical lobe of one bract not saccate and that of the other bract seemingly replaced by two, free paraphyllia-like leaves). Perianth present; elongate, suddenly narrowed to the mouth with about twelve small, triangular ciliate lobes; but sometimes replaced by tubular, cylindrical, smooth and wide-mouthed ‘sterile perianths’, which are another unique feature of the family. Perianth deeply distally plicate.

Sporophyte. The sporophyte elevated by elongation of the seta, with no intercalary meristem. Elaters present; bispirally thickened; free.

British representation. 1 species (P. purpurea); Scotland and Ireland.

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

Comments. Pleurozia is further peculiar among Jungermanniales in having an apical cell with only two cutting faces. Illustrations. • P. purpurea: Jameson, in Macvicar (1926). • cf. P. purpurea (as P. cochleariformis): Pearson fig. XXXIII (1902). • cf. P. purpurea (as P. cochleariformis): Pearson fig. XXXIII legend.

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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.’.