Monday, 26 June 2017

Post-flowering fate of Man Orchids at Ufton Fields.

Ufton Fields, a Warwickshire Wildlife Trust reserve, has a small population of Man Orchids (Orchis anthropophora).  In late May we counted 5 flowering spikes among the 25 cages marking plants that are, or have at one time been seen, there. In addition 2 more plants were in bud.  There were no plants outside the cages.  Excluding one of the 5, which was spindly and frail the average height of a flower spike was 26cm with 27 flowers on average.
Man Orchid in Fruit

Ufton Meadows - Man Orchid Cages

A frail plant that simply withered

I went back this morning to see the fate of these plants.  Without the cages they would have been impossible to find in the developed sward.   Lady's bedstraw and St John's-wort were everywhere.

The two plants that were in bud did not develop and had died off, as had the frail plant.   This left 4 spikes which had developed fruits with a total of 34 seed pods. Including the frail plant there were originally 123 flowers, so the fruiting success was 28%.  The fruiting success of individual plants varied from 0 (the frail plant) to 42%.

Last week we carried out a similar exercise at Bernwood Meadows, but not very successfully.   In early May we counted the flowers on 174 flowering spikes of Green-winged Orchids (Anacamptis morio) which averaged 6.8 flowers per spike in a survey area we created.   We went back to count fruits, at lunchtime on one of the hottest days of the year last week.   This is not an excuse for the fact that we could only find 31 of the original 174 flowering plants.  Those had an averages of 3 seed pods and 7.9 flowers.  The apparent fruiting success was therefore 38%.   But what of the plants that we could not find, which appear to be those with fewer flowers?  The total number of flowers we counted was 1193 and the total seed pods we found was 93; on this measure the fruiting success was only 8%.   The survey at Ufton Fields shows that unless individual plants can be identified in flower then again in fruit, assessment of the fruiting success is extremely difficult.
Bernwood Meadows
Fruiting Green-winged Orchid

Monday, 5 June 2017

Fruiting of Early Purple Orchids at Westwell Gorse

The Early purple orchids (Orchis mascula) are now in fruit at Westwell Gorse. 

In flower 4 May
In fruit 2 June

In flower 4 May
In fruit 2 June (top chewed)
In early May we measured the height and counted the number of flowers on 83 plants in a survey area we designated.  We went back on Friday to count the number of seed pods in order to estimate the fruiting success.  We found 63 plants; once the sward is higher it is  challenging to find just the fruiting plants.   For each we counted both the number of seed pods and the number of dead flowers that had not fruited.   From this we estimated the fruiting success at 36%, but it needs correcting.   In May the average number of flowers per plant was 9.8, whereas last Friday we got a lower figure of  8.6.   Either we missed some of the larger plants with more flowers, or more likely some of the buds that we originally counted as flowers did not develop, but just fell away.  If we apply an adjustment of 8.6/9.8 for the number of flowers then the fruiting success falls to 31%, which by coincidence is the same figure as in 2016.

The figure compares with references given for some German studies by Claessens and Kleynen in The Flower of the European Orchid ranging from 7 to 67% with an average of 34%.  Results from Sweden quoted in the same text were lower.   A Norfolk study (Hardy Orchid Society: April 2013) got a much higher result, 84%.  That looks atypical.

The range across individual plants was from zero to uncommonly 100%, with no real pattern.   The chart below plots Fruiting success (Y-axis) against Number of flowers per individual plant (X-axis)

It was noticeable that flowers at the top of the spike - those flowering later - were less likely to be pollinated, though we made no attempt to quantify the effect.

Pyramidal orchids were just coming in to flower, whilst there were 10 plants of Purple Milk Vetch, which is on the Red Data List.
Pyramidal Orchid

Purple Milk Vetch