Look out for this new species of Conocephalum
Ken Adams 63 Wroths Path, Baldwins Hill. Loughton. Essex. IG10 1SH
Our largest thalloid liverwort, Conocephalum conicum is one of the most readily
identified. It is up to 12mm wide and 15cm long. It's rather like the liverwort Marchantia
that occurs in greenhouses, but that has little splash-cups on its surface that bare gemmae,
small disc-like propagules dispersed by raindrops. Conocephalum conicum is brittle
and more leathery than Marchantia. Both however, are covered with a network of
diamond-shaped lines that demarcate air cavities in the thallus beneath the epidermis,
each diamond-shaped cavity being surmounted by a domed pore that enables the air
cavities to exchange gases with the atmosphere. Conocephalum grows on clay river
and ditch banks, and on walls by rivers; and sticks tenaciously to its substrate. It has a
characteristic smell of a cross between turpentine and a mushroom.
Until recently, only one other species was known, anywhere in the world. This is C.
japonicum (=supradecompositum) found in Asia and Japan (and a few glasshouses in
this country). One obvious difference is that it produces large yellowish tubers from the
apex of the lobes. However, Szweykowski et al in a series of papers starting in 1991,
found that both'C. conicum' and 'C. japonicum' each consisted of two isoenzyme distinct
entities giving us four genetic variants World wide. Just recently, they discovered that
the two isotypes of C. conicum, could be distinguished both morphologically and
anatomically. The new one is called C. salebrosum, and has been found to occur in
Europe, (including Britain in limestone areas), eastern Asia and in N. America, but so
far, no material corresponding to the type material of C. conicum sensu stricto has been
found outside Europe, thus the Americans are having to rename all their herbarium
material C. salebrosum.
The differences between the two are anatomically fairly clear-cut, but the external
morphology is more subtle. True C. conicum is bright green, smooth and glossy; with
the diamond-shaped surface lines less conspicuous than the pores, the epidermis
seemingly skating smoothly over the vertical walls that define the air cavities. C.
salebrosum on the other hand, is dull, with the outlines of the cavities more obvious
than the pores, because the epidermis is undulating, with the surface following the
intervening cavity walls as anctwork of grooves which under the microscope is revealed
as a single line network of smaller cells. Cutting a section reveals that these smaller cells
are the top cell rows of the vertical cavity walls, which are inserted in-between panels of
epidermal cells; whereas in C. conicum s.s. the epidermis is continuous, and the tops of
the walls appear to be simply butted beneath the upper epidermis. Underneath each
domed pore, a layer of closely packed, pointed, chloroplast-free cells form a circular
patch. Their function is unknown, but their location suggests they may possess a CO2
concentrating mechanism. These cells are subtly different in shape between the two
species. In C. conicum they are like a rather long-necked conical flask with more or less
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Essex Field Club Newsletter No. 49, January 2006