Nature girl's picture

Common Polypody

Observed: 12th March 2011 By: Nature girl
Royal Society for the Protection of Birds
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Species interactions

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Chris Metherell's picture

Polypodium spp.

At the risk of being rude, perhaps you, or perhaps those who agree, could explain why this is P. vulgare and not P. interjectum?

Chris Metherell
BSBI VC Recorder
North Northumberland

Nature girl's picture

Common vs. Western

Sorry, I should have put details with the ID. I posted it without giving it much thought but now looking at how similar the two species are I can see that you make a good point.

From a more detailed look at P. vulgare in my Collins guide:

- the spores are rounded, whereas those of P. interjectum tend to be more elliptical
- the ends of the pinnae are relatively blunt, whereas those of P. interjectum would be more pointed
- the base of the leaf is more or less rectangular, whereas that of P. interjectum would taper at the base
- also, it says in my guide that the spores of P. vulgare are ripe until March and for P. interjectum it says only until February. Although I wouldn't rely on this as a distinguishing feature, this observation was made in March so it makes me lean more in favour of P. vulgare.

Hope this helps,


AlanS's picture


I am not posting a revision, for as far as I am concerned, any polypody that has not had the thickened cells of its sporangium annulus counted (or its chromosomes) is automatically 'P. vulgare aggregate'.

So we are guessing here. However, I am with Chris, it looks like P. interjectum to me, as far as can be judged on macro-morphological grounds.

The rounded/elliptical shape of the sori is not a reliable character and varies in the photograph. The pinna tips can be rounded to pointed in both species.

The spores have evidently been discharged from the sporangia for some time, so there is no help there.

The photograph of the back of a frond at highest magnification shows the annuli, but unfortunately not clearly enough to allow counting of the cells. However, the annuli are quite pale, the typical colour of P. interjectum, rather than the distinctly contrasting, rust-brown of P. vulgare.

So yes, on balance, I think it is mre likely to be P. interjectum.


Nature girl's picture

Thanks Alan

I won't be so hasty next time on the ID. I don't really know much about ferns at the moment and it seems I have much to learn!