Conocephalum conicum (L.) Dumort.   

Kingdom: Plantae
Phylum: Bryophyta
Class: Hepaticopsida – liverworts
Order: Marchantiales

British distribution: Throughout Britain.
World distribution: Europe (closely related taxa in Asia, N.Africa, N.America).

Conocephalum conicum is one of our most common 'thallose' (i.e. not leafy) liverworts, often forming large colonies on damp, shady stonework and on ditch sides and in damp woodland. The photographs show it growing on the faces of rocks in the river here in Paisley; commonly the water flows over these rocks and the Conocephalum is behind a small waterfall.

Morphology and anatomy
As is typical of the Marchantiales, the gametophyte thallus is dichotomously branched and many cells thick, with tissue differentiated into the chlorenchyma - an upper region of small cells containing chloroplasts, and a lower parenchyma of larger cells containing starch grains. There are well developed epidermises and the ventral surface also possesses scales, in this case rather sparse in single rows on either side of the midrib. The upper epidermis contains air pores (somewhat analagous to stomata in the sporophyte generation of vascular plants). In Conocephalum these air pores are surrounded by 4-6 concentric rings of thin-walled cells, making the pores easily visible to the naked eye.

Only the vegetative thallus is shown here, but this species frequently produces receptacles at the thallus apices. The male receptacle (containing the antheridia) is sessile, green or tinged violet, while the female receptacle (containing the archegonia) is stalked, like a tiny umbrella, the stalk sometimes elongating to up to 10 cm.
Conocephalum is, however, dioecious (male and female gametes produced on separate plants) and colonies will often be of a single sex. Sporophytes are rare, though said by Paton (1999) to be more frequent in southern and western Britain.

Asexual reproduction is usually by regeneration from broken pieces of thallus, the thallus being brittle and no doubt easily transported by water. Gemmae, of the type seen in some other large, thalloid liverworts, are not produced, but tubers sometimes develop on the lower surfaces of senescent thalli (Paton, op. cit.).

Until recently this was believed to be the only British species of Conocephalum. However, molecular studies have shown there are other, "cryptic" species in this complex and a second, morphologically distinguishable entity occurs widely in the Northern Hemisphere, including in Britain (Szweykowski et al., 2005). This is C. salebrosum, now known to be widespread here, distinguishable in the field by its somewhat smaller size and duller thallus surface with more conspicuous reticulation. Further details are on the British Bryological Society's website, link here.
The two species can occur together, perhaps frequently so.

Paisley, Renfrewshire, Scotland, May 2002.

•   Paton, J. A., (1999). The liverwort flora of the British Isles, Harley Books, Colchester.
•   Szweykowski, J., Buczkowska, K., & Odrzykoski, I.J., (2005). Conocephalum salebrosum, (Marchantiopsida, Conocephalaceae) – a new Holarctic liverwort species. Plant Systematics and Evolution 253: 133-158.

© A.J. Silverside
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