Its approaching the end of the season for many of our ferns so I have been doing a bit of revision, trying to familiarise with some of the local species and where they live. In the process I have been using a selection of fern identification guides, and trying to find what approach works for me.
There seems to be 2 approaches. A more traditional one used by Stace, CTW and Hutchinson that identifies ferns by family or genus, and one based on leaf structure employed by Merryweather and Poland and Clement.
The former work like this Step 1; fertile/non fertile fronds. Step 2; leaves entire or pinnate, Step 3; Marginal or superficial sori. etc.
The latter work like this Step 1 Leaves entire, Step 2 Leaves 1- pinnate, Step 3 Leaves 2-pinnate etc.
Both are going to have their advantages and disadvantages but the main problem for either approach is the differences in definitions of the parts of the plant. This is highlighted by the definition of whether a leaf is pinnate or not. Male ferns are classed as 2-pinnate by Merryweather but 1-pinnate/pinnatisect by Poland and Clement. Polypody is pinnate according to Streeter but pinnatisect according to Poland and Clement while Stace says they can be both.
I understand that the degree of division is difficult to see and a destructive approach often taken to teaching the structure, in other words the leaf is taken apart starting with the smallest division (pinnule). The problem is that if the first division is not a pinnule but actually a lobe then the system is bound to cause confusion especially when compared with a different book that uses the same words to describe different parts of the plant.
The other issue for me especially with beginners guides is that they tend to take the user through all the uncommon stuff first. In Merryweather for example Bracken which is the most abundant fern in the country (if not the world) is one of the last species in the book.
So do the inherent variability yet similarity of ferns make it too difficult for them to be described in a straighforward way?