Ptyxis Ecology - Our Botany Blog

Saturday, 14 June 2008

Small-white orchid and bluebell banks

The Weardale Gazette recently reported that "John O'Reilly excited himself by finding a rare plant in a meadow near Wolsingham". The rare plant in question was Alchemilla acutiloba which is not that rare in Weardale but is very rare elsewhere. Well, yesterday I 'excited myself'' even more by finding 8 spikes of small-white orchid Pseudorchis albida on a bank in the Holwick area of Teesdale. Out of about 450 meadows that I've surveyed so far this is only the 2nd time I have found it and the other time it was shown to me by Linda Robinson.

I surveyed this meadow on 5th June and was puzzled by this orchid spike in bud:

I assumed at the time that it was probably Platanthera chlorantha which is quite uncommon and a nice thing to find, but it didn't look quite right. The flower buds showed no sign of the elongated pedicels you would expect with greater butterfly-orchid but I thought that might just be because of the early stage of development. But the stem leaves seemed too big and the flower buds were very numerous and congested on the spike. I thought the stem leaves and overall shape of the spike was right for Pseudorchis but I doubted it was that because the plant was about 10 inches high already which I thought was too big and also because it is so rare around here.

So here it is in all its glory 8 days later:

It is not the most spectacular-looking species in the world but a nice find beacuse it is so uncommon and it usually indicates very nice habitat. One of the best things about it was that I told the farmer that I found it and he rang me back later on to ask how could he grow more of them on the bank!

I didn't take a proper habitat shot but you can see some of the associated species in this shot:

If you look closely you will see lots of leaves of Succisa pratensis and Hyacinthoides non-scripta, some Potentilla erecta and Conopodium majus a flowering stem of Festuca rubra, and STOP PRESS!..... I've just this minute noticed something with a spike of flowers in bud in the bottom right hand corner which I think is Persicaria vivipara - I will have to go back again to check that out.

This bank was quite large, about 15-20 metres top to bottom and about 100m long, the vegetation was fairly homogenous throughout. The dominant species were Devil's-bit scabious, bluebell, pignut, tormentil and creeping soft-grass. I was very puzzled as to what this would be in the NVC but I think I've worked it out now. One of the best places to look for Pseudorchis albida in upland hay meadows is apparently in U4c vegetation on banks (see my blogs from last year about banks in meadows). I think the vegetation above is a form of MG5c which grades into U4c depending on the soil characteristics. The main difference between the two is the grass component of the flora. MG5c has more of the broad-leaved bulkier grasses (here it had both Holcus species, Dactylis glomerata and Helictotrichon pubescens) and bulkier herbs like Centaures nigra, whereas the dominant grasses in U4c tend to be fine-leaved species like Festuca rubra and ovina and Agrostis capillaris.

Bluebells are a prominant feature of grasslands in meadows in Teesdale and in the Greta valley. In the NVC bluebell does not feature prominently in any of the tables describing the published grassland communities, so it has taken me a while to work out which communities are involved. Not far from the bank described above it occurs in another very large bank in vegetation with some similarities to the type of MG5c described above, except that in has some more typical acid grassland indicators like Galium saxatile and has a canopy of bracken. This 2nd type of vegetation is clearly a good match to U20a.

A third type of grassland where it occurs abundantly is almost identical to the U20a except that it has no bracken. So you could call this either 'U20a without bracken' or 'U4a with lots of bluebell'?

A forth type is quite common in narrow strips along the base of walls or along the lines where there used to be a wall within a field. This vegetation has clearly developed along these walls since they were erected and is not relict woodland vegetation. Usually the vegetation is overwhelmingly dominated by Holcus mollis and Hyacinthoides non-scripta, sometimes with the odd bit of Urtica dioica, Dactylis glomerata, Dryopteris filix-mas or Conopodium majus. This vegetation is an excellent match to W25a, except that there is no bramble or other woody species. Perhaps it is a stage in the development towards W25a!

It also occurs in more typical MG3 and the richer forms of MG6 that grade into MG3.

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