Saturday, 15 March 2014

Tallington Teasers

On Sunday I spent a couple of hours recording around Tallington village, in TF00Y and TF00Z. The weather was perfect, and many of the spring ephemeral species were in full bloom, particularly Erophila verna, which seems to be having a bumper year. 

One of the more puzzling pairs of white Brassicaceae are hairy bittercress Cardamine hirsuta and wavy bitter-cress Cardamine flexuosa. The most reliable character to separate this species pair is the number of stamens, which is normally four in C.hirsuta and six in C.flexuosa. However, sometimes these can be hard to see, even with a good hand lens. The habitat gives a good indication - C.hirsuta is usually in open and cultivated ground, on rocks, walls and pavements, and can be a major garden weed. C.flexuosa is usually in more shaded and damper areas, particularly in marshes and streamsides, and tends to look noticeably taller and lusher. At Tallington, C.hirsuta was frequent, but I found one small population of C.flexuosa along the banks of the River Welland.

Cardamine flexuosa showing the six stamens

The hedgerows were brightened by lesser celandine Ficaria verna and locally abundant sweet violet Viola odorata, which was present in several colour forms. Most were the characteristic bluish-purple of V.odorata var. odorata, but there were some populations of V.odorata var. dumetorum, which has a violet-purple spur with whitish petals (sometimes splashed purple) and the lateral petals bearded. You can see a couple of examples below.

V.odorata var. dumetorum, showing purple spur and white petals
Purple-splashed petals with bearded laterals

One of the most interesting species I found was a specimen of intermediate polypody Polypodium interjectum growing on a shaded north-facing limestone wall, together with black spleenwort Asplenium adiantum-nigrum. Polypody ferns are distinctive but can be quite awkward to identify to species, and really require microscopic examination of the sporangia. The only two species which occur in our area are common polypody P.vulgare and intermediate polypody P.interjectum, and both are very local. Their habitat preferences can assist with correct identification: P.interjectum generally prefers more basic substrates including limestone walls and the bark trees such as ash. P.vulgare grows on acidic substrates, including granite walls, non-limestone rock outcrops and as an epiphyte on acid-barked trees such as oak. If in doubt, polypody can be recorded as Polypodium vulgare sens. lat.

Polypodium interjectum on a limestone wall. Note oblong-lanceolate shape of fronds (scarcely parallel-sided).

No comments:

Post a Comment