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

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L. Watson and M. J. Dallwitz

Colura (Dum.) Dum.

Gametophyte. Plants minute, leafy. The branching of the Lejeunea type (with the branches somewhat ascending). The stems with cortical cells clearly differentiated from the cells of the central strand (transverse sections exhibiting 3 central cells surrounded by 7 corticals). Acrogynous. Rhizoids present; colourless (in bunches associated with the lateral leaves).

The leafy shoots dorsiventral, with two equal ranks of lateral leaves and a third, ventral rank of smaller underleaves. The vegetative leaves very narrowly, more or less transversely inserted; alternate; erect or ascending, overlapping to distant; bilobed (the dorsal lobe reduced and shorter than the ventral one, ovate to orbicular, overlapping the stem and decurved, the larger ventral one being distally sac-like and abruptly narrowed into a beak constituting 1/2–1/3 of the leaf length; the proximal margins are inrolled to form a channel leading to the sac, the opening of which is protected by a moveable flap); complicate-bilobed. The ventral lobes larger than the dorsal lobes; without a stylus. The vegetative leaves without vittae. Underleaves smaller than the laterals though well developed and conspicuous (double the common number, there being one associated with each lateral leaf, bilobed almost to the base, the usually subulate lobes not divergent); bilobed. The lobes not divergent. The cells of the gametophyte with numerous small chloroplasts. Gemmae common (discoid, on the leaf surfaces and especially on the beaked sac of the dorsal lobe).

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

Male inflorescences on very short lateral branches, small, globose, with 3–5 pairs of strongly concave emerginate bracts subtending pairs of brown, broadly ovoid antheridia, and bracteoles throughout. Male bracts subtending 2 antheridia. Female inflorescences terminal on main axes, and often produced successionally via single innovations commencing under the first. Female bracts present (small, strongly concave, entire or emarginate to shallowly bilobed). Bracteole present (much reduced), or absent. Perianth present; long exserted beyond the bracts but not the leaves, clavate from a very narrow base, the unicellular beak very short but distally 5-keeled with each keel ending in a hornlike process. Perianth distally plicate. Perianth distally beaked.

Sporophyte. The sporophyte elevated by elongation of the seta, with no intercalary meristem. The capsule globose; dehiscing by four valves. The spores unicellular when shed. Elaters present; unispirally thickened; persistent on elaterophores (orientated vertically in the unopened capsules and extending to the floor, remaining attached by their upper ends to the inner walls of the distal ends of the dehiscing capsule valves and their trumpet-shaped lower ends becoming free).

British representation. 1 species (C. calyptrifolia); England, Wales, Scotland, and Ireland.

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

Illustrations. • C. calyptrifolia: Jameson, in Macvicar (1926). • C. calyptrifolia (as Lejeunea): Pearson fig. XX (1902). • C. calyptrifolia (as Lejeunea): Pearson fig. XX, 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.’.