Polypodium vulgare × P. interjectum
(P. × mantoniae Rothm. & U. Schneid.), a hybrid polypody

Account Summary

Growth form and preferred habitats

All ten records for this sterile pentaploid hybrid in the Fermanagh Flora Database have been determined by Paul Hackney working on specimens deposited in the herbarium at BEL. The most recent eight were collected by RHN either growing in moss on rocks or as epiphytes on tree trunks in damp old woods. In view of the frequency of the parent species and their degree of ecological overlap, this intermediate hybrid is probably quite widespread and is likely to be the most common of the three sterile Polypodium hybrids.

In a W European study assessing the pH preferences of ferns and their root cation-exchange properties and preferences, Koedam et al. (1992) found that P. × mantoniae follows its tetraploid parent P. vulgare s.s. in being 'acidiphilous' (ie strongly calcifuge), since it occurred on soils with a median pH value as low as 3.8. Furthermore, no calcium carbonate was detected in any of the soil samples taken from the roots of this fern hybrid. On the other hand, Page (1997) reported it occurring in humid conditions on mossy boulders over a wide range of rock types including limestones.

British and Irish occurrence

Page (1997) reported that this hybrid had been found in at least 29 VCs in Britain & Ireland and that the distribution was slanted towards western areas. The New Atlas hectad map shows that P. × mantoniae is now known quite widely across Britain and N Ireland, and it occurs on soils derived from both siliceous acid and limestone rocks.

Reproduction

Although this is usually regarded as a highly sterile hybrid, some of the plants appear to have a high proportion of apparently normal spores. The backcross with P. vulgare s.s. has been suspected in at least one of the Fermanagh records. This hybrid is vegetatively vigorous and can form large clones.

Fermanagh occurrence

The details of the other nine Fermanagh records follow with their collector; all were determined by P. Hackney and vouchers exist: Finlane Td, Florencecourt Forest, 1976, P. Hackney; scarp SW of Lough Achork, December 1987, RHN; Castle Archdale, Lower Lough Erne, December 1987, RHN; Ely Lodge Forest, Lower Lough Erne, February 1988, RHN; Sillees Wood, March 1989, RHN; Clonelly, NW of Kesh, April 1989, RHN; Arney River, April 1989, RHN; Crossmurrin NR, December 1989, RHN; Ballindarragh Bridge, Colebrooke River, 1988-90, RHN. The last listed record is considered a possible backcross with P. vulgare s.s.

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