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

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L. Watson and M. J. Dallwitz

Porella L.

Including Madotheca.

Gametophyte. Plants robust, yellowish-green, green or brown leafy. Basally rhizomatous, the branching lateral, 1–3 pinnate. The branching of the Frullania type. The stems with cortical cells clearly differentiated from the cells of the central strand (the cotical cells thick walled and soon becoming pigmented, the medullary cell walls thin and hyaline). Acrogynous. The leaf cells with trigones, or without trigones. Rhizoids present (but often scarce, arising from the underleaves); brown.

The leafy shoots dorsiventral, with two equal ranks of lateral leaves and a third, ventral rank of smaller underleaves. The vegetative leaves obliquely inserted, or with J-shaped insertion; overlapping; incubous. The leaf margins mostly entire; not multi-ciliate. The vegetative leaves conduplicate- bilobed (almost to the base, with only a very short or vestigial keel, the orbicular to lanceolate, entire or dentate dorsal lobe very much larger than the ligulate, linear or ovate ventral one, which differs from that of Ptilidium in lacking an internal water sac); complicate-bilobed; leaves keeled proximally to the lobes to not keeled. The ventral lobes much smaller than the dorsal ones. The vegetative leaves without vittae. Underleaves smaller than the laterals though well developed and conspicuous (present everywhere, resembling the ventral leaf lobes but broader and often basally decurrent on both sides). The cells of the gametophyte with numerous small chloroplasts. Gemmae absent.

The plants dioecious.

Male inflorescences on dwarf lateral branches, shortly spicate, the imbricate, almost equally bilobed bracts perfectly opposite and connate with the underleaves. Male bracts subtending a single antheridium. Female inflorescences on dwarf lateral branches. Female bracts present (usually a single pair, usually dentate or ciliate). Perianth present; sub-ovoid, often dorsally compressed distally, trigonous in section, the mouth becoming bilabiate or campanulate by extrusion of the capsule. Calyptra present and well developed (of several cell layers).

Sporophyte. The sporophyte elevated by elongation of the seta, with no intercalary meristem. The capsule shortly pedicellate, globose; dehiscing by four valves (these often irregularly split and rarely separating down to the base). Elaters present; short, bispirally thickened, or thickend via 3–4 spirals; free.

British representation. 5 species; England, Wales, Scotland, and Ireland.

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

Illustrations. • P. arboris-vitae (as Madotheca laevigata): Jameson, in Macvicar (1926). • P. arboris-vitae (as laevigata): Pearson fig. XXVIII (1902). • P. arboris-vitae: Pearson fig. XXVIII legend. • P. cordaeana (as Madotheca): Jameson, in Macvicar (1926). • cf. P. obtusata (as P. thuja): Pearson fig. XXIX (1902). • P. obtusata (as P. thuja): Pearson fig. XXIX legend. • P. pinnata (as Madotheca porella): Jameson, in Macvicar (1926). • P. pinnata: Pearson fig. XXXII (1902). • P. pinnata: Peason fig. XXXII legend. • P. platyphylla (as Madotheca): Jameson, in Macvicar (1926). • P. platyphylla: Pearson fig.XXX (1902). • P. platyphylla: Pearson fig. XXX legend. • P. rivularis: Pearson fig. XXXI (1902). • P. rivularis: Pearson fig. XXXI 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.’.