Mixed fortunes for one of our rarest plants

7th July 2009, Tuesday

Both of the (introduced) East Sussex populations of the rare stinking hawk’s-beard Crepis foetida have increased in numbers this year.  At Rye a minimum of 1035 plants were present, a major increase from the previous highest total of 417 plants last year.  This significant increase was down to the creation of another fenced plot from which rabbits were excluded two years ago.  This now contains 79% of the plants, and most of the larger specimens.  The original plot may be getting a little overgrown, and may benefit from some deliberate scarification of the gravel to see if this produces better growing conditions.  As in previous years a few plants were found growing outside of these plots until they started to grow tall flowering stems and attracted lagomorph attention.

At Northiam there was a more modest increase in numbers, from 139 plants recorded last year, to 163 so far.  This is well down on the previous best of 1225 plants three years ago.  It has made an interesting study though.  It is quite clear that this plant does very badly in wet summers.  Whilst three years ago there were thousands of young seedlings, in 2007 only 50 seedlings germinated on the limestone bed this plant normally thrives in, and this fell to only 22 plants last summer.  Both years were characterised by much more rain than normal, and the seedlings either did not germinate, or died shortly afterwards as a result.

At one stage I feared the plant might actually be threatened with extinction last winter, however another case of environmental variability came to its rescue.  Last winter was unusually cold, and this was marked by very good survival of the young seedlings. 19 of the 22 plants on the limestone bed survived to flower, an unusually high level (86%).  The reason for this was apparent in the healthy state of the leaves over the winter with an absence of grazing damage, and an absence of mollusc activity at night during the frosty weather.  It’s interesting to see that what is essentially a southern European plant actually benefited from a harser winter.  The expected mollusc grazing damage did not materialise until mid March when the first two damaged leaves were found, which is very late.

This summer the weather seems to be more conducive to successful germination, with long periods of warm dry weather burning off lawns, and providing an ideal bed in which seedlings can germinate.  And today I found the first of next years plants had germinated – see photo.  The damage to the leaves is not mollusc grazing, but is due to deliberate damage by me to reveal the characteristic smell that renders such tiny seedlings identifiable.

Just to lower right of the sedling you can see the white pappus of another fallen seedling – it’s notable how many of these wind-dispersed seeds actually fall around the parent plants.