A useful way of identifying ferns can be to look at pictures and it doesn’t take long just to flick through the pages of Streeter (2009) to find Maidenhair Spleenwort A trichomanes but it looks very similar to A viride. By reading the descriptions of each plant it is possible to accurately identify the species. .( A viride has a green not dark stipe and rachis.)
The other alternative is to use a key to identify the plant looking at particular characteristics such as size, leaf shape, sori shape etc. This means taking a very close look at the plant using a hand lens and then answering various questions about its diagnostic features until hopefully the correct conclusion is reached. In Streeter (2009)on page 32 there is a separate key for Aplenium Spleenworts which shows how this works. (1- Pinnate means 2 rows of leaflet along a single axis)
1. leaves irregularly and sparsely forked into narrow linear segments
Leaves 1 – 3 pinnate, lobes not linear 2
2. Leaves pinnate 3
leaves 2-3 pinnate 5
3. Upper part of rachis with green wing, leaf thick and glossy, pinnae
less then or equal to 15mm ( sea cliffs, caves)
Rachis not winged, pinnae less than 12mm 4
4. Rachis black A trichomanes
This is a tracing of an individual leaf blade of A trichomanes. The central stalk is called a stipe near the base where there are no leaves. Where there are leaves the central stalk is called a rachis. Either side of the rachis small leaflets are connected called pinnae. I sketched an enlarged illustration of an individual pinna showing how it is attached to the rachis with a very small stalk. The outline is not straight but slightly wavy. As this is the underside of the pinna it is possible to determine the shape of the 5 sori which are very pale, could they be next year’s fertile sporangia? At 8cm long and with pinnae of about 4mm this plant is well described in Streeter (2009).
This is the same leaf blade I traced, viewed from underneath, showing the dark stipe and rachis as well as the pale sori shapes on the individual pinna.