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

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L. Watson and M. J. Dallwitz

Petalophyllum Nees & Gott. ex Lehm.

Gametophyte. Plants thalloid, with a short, basal, cylindrical tuberous portion obliquely embedded in the substrate, preceding a prostrate, fan-like winged exension with a semi-circular midrib and erect, unistratose dorsal lamellae radiating from the midrib to the wing margins. Simple or branched. Anacrogynous. Rhizoids present; colourless, or brown; of one kind, all smooth.

The cells of the gametophyte with numerous small chloroplasts. The thallus simple, or branching dichotomously; without ventral scales. Gemmae absent (perennating via proliferations from under the midrib). The thallus without dorsal pores; without cavities.

The plants dioecious. The antheridia more or less globose, protected by bracts.

The archegonia and sporophytes in groups, protected by bracts (these laciniate). The archegonia and sporophytes with a pseudoperianth (this widely campanulate, the mouth lobed). Bracteole absent. Perianth absent. Calyptra present and well developed (only slightly shorter than the pseudoperianth, surrounded at the base by sterile archegonia).

Sporophyte. The sporophyte elevated by elongation of the seta, with no intercalary meristem. The capsule globose. The capsule wall 3–4 layered (the inner layer with semi-annular thickenings). The capsule brownish-blackish, not green; dehiscing via a single longitudinal slit (at first), or dehiscing irregularly (by subsequent ruptering). The spores unicellular when shed (with 4–6 hexagonal areolae on the convex face). Elaters present; bispirally thickened, or thickend via 3–4 spirals (2–3 spiral); free.

British representation. 1 species (P. ralfsii); England, Wales, Scotland, and Ireland.

Classification. Class/Division Hepaticae. Subclass/Class Jungermanniidae. Order Metzgeriales. Family Codoniaceae.

Comments. The more or less globose antheridia scattered on the upper surface over the midrib, protected conical or dome-shaped scales; the archegonia in groups on both sides of the dorsal surface of the midrib towards the apices, protected by laciniate bracts within which the pseudoperianth forms after fertilization. Illustrations. • P. ralfsii: Jameson, in Macvicar (1926). • P. ralfsii: Pearson fig. CXC (1902). • P. ralfsii: Pearson fig. CXC 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.’.