Stinking Hawk's-beard Crepis foetida Subsp. rhoeadifolia in Cambridgeshire.
|Crepis foetida subsp. rhoeadifolia
In late July the BSBI County Recorder, Jonathan Shanklin found an interesting Crepis at Hobson's Park next to Addenbrooks Hospital. With the help from Alan Leslie and his vast library, it was identified as Crepis foetida subsp. rhoeadifolia. Unlike the native species Crepis foetida subsp. foetida which hangs on at Dungeness and Rye, rhoeadifolia is a plant of central and south-eastern Europe. One has to assume it arrived in a seed mix. This sub-species has not been recorded in Britain for many years.
The crepis group are complex, with a large number of species displaying "reticulate evolution via hybridization across lineages or of incomplete lineage sorting". Where have I heard of that before? Roses!
Anyway if you want to know about the genetics of Crepis foetida and other species in this group, a PHD thesis by a lady from Libya was done at the University of Giessen in Germany and its conclusions make interesting reading even if the detailed genetics are in my case, above my pay grade and understanding.
I think the conclusion of her work, is that Crepis foetida subsp. foetida and Crepis foetida subsp. rhoeadifolia should remain as sub-species but that the third subsp. Crepis foetida subsp. commutata should be regarded as a separate species Crepis commutata.
Where both subspecies grow together, intermediates do occur. Having said that, in many places there are distinctive features that separate the two subspecies. Flower size is 20-30mm diameter in rhoeadifolia and 15-25mm in foetida, the outer phyllaries (involucral bracts) are longer in rhoeadifolia and also wider being 1-1.5mm wide against only up to 0.75mm in foetida. Both lack the translucent scales on the receptacle that are present on Crepis commutata.
First impressions were that this was not like any of the normal species found in Cambridge. The capitulum had a rather wide onion shape and it was still in flower at this late date. The flowers were up to 32mm in diameter, bright yellow with some red banding on outer ligules. Plants had a basal rosette of leaves and several stems with few middle and upper leaves which branch to support the flower heads.
The first photo above shows structure and some flower buds are drooping, although at this stage most flowers are beyond the 'drooping in bud' stage and are held upright. The involucre, stems and leaves all had simple grey hairs which gave the plants a grey look.
|The first plant, found beside the path with prominent white pappas extending well beyond the phyllaries.
|Typical plant showing many upright stems and the greyish look.
Crepis vesicaria ( Beaked Hawk's-beard) had long ago finished flowering and even its seed heads had lost their achenes. Crepis biennis (Rough Hawk's-beard), although later than vesicaria, had also finished flowering, except for a few late examples. Crepis capillaris (Smooth Hawk's-beard) was still in flower but with much smaller flowers.
|Comparison of C. biennis against Crepis foetida subsp. rhoeadifolia showing wide capitulum and
very prominent white pappus. 25th July 2023.
Jonathan had also spotted that the outer achenes were a shorter length and less beaked compared to all the inner ones. This is a feature which excludes all native Crepis except for a sub-species of C. vesicaria called Stellata, a native of Morocco which according to Sell and Murrell, has been found in Cambridgeshire. There would be some doubt over this tentative identification, which is named subsp. gigantea in Alan Leslie's Flora of Cambridgeshire. Stellata did not fit with the plants at Hobson's Park but it took some time to exclude it. It has according to Sell and Murell, involucral bracts with dense , long and short , greenish or dark glandular hairs. It also has discoloured stigma.
|Achenes of subsp. rhoeadifolia.
The shorter outer achenes are clasped by the inner involucral bracts (phyllaries).
|Shorter outer achenes are held in the involucral bracts long after the longer achenes have blown away.
Note the cillate hairs on the receptacle.
Note the yellow stigma matching the yellow of the ligules. Some darkening did occur as the flowers aged. The diameter of flowers was up to 33mm which fits the range of rhoeadifolia against foetida which has range 15-25mm.
|Outer bracts are very variable in length but the longest are well over 50% of the inner.
|Phyllaries have simple grey hairs and cobwebby hairs. At this stage the phyllaries are starting to spread in the cup and saucer shape typical of some Crepis species.
|Basal rosette of leaves.
The basal leaves of some Crepis species can be highly variable and highly complex. Crepis biennis ( Rough Hawk's-beard) being especially variable making leaf shape not very useful as an identification feature. It would appear that Crepis foetida has a more consistent basal leaf shape in that the basal leaves have a spade shaped tip which tapers down to its base, with triangular lobes at least for British illustrations of both sub-species. This may not be true over its whole range, as a publication on Bulgarian Flora has illustrations which show a much more irregular shape.
|Mid Stem leaf . A more pointed version of the basal leaf.
|Many hundred plants present at this site suggests it has been present for several years. It has also spread into the adjacent field.
Differences between the two sub-species foetida and rhoeadifolia.
Not having seen foetida in the wild, puts me at a major disadvantage, so maybe next year a trip down to Rye in Sussex would be a good idea. Strangely, the re-introduction program of C. foetida subsp. foetida used plants grown at the Cambridge Botanic Gardens, however none seem to have escaped and the area around has been well covered over many years.
Rhoeadifolia can grow to 80cm whereas foetida is usually limited to 50cm. It would appear from photos of foetida at Dungeness and Rye, that it is often a smaller plant and may be greener and not so grey. Maybe the density of the grey hairs on the leaves, is a particular feature of the Hobson's Park population.
|C. foetida subsp. foetida
|C. foetida subsp. rhoedifolia
Hopefully the above photos help to document this sub-species, which was a great find by Jonathan Shanklin and he has written up a short account for the April 2024 edition of BSBI News.