Monday, 29 March 2021

Rosa stylosa. Short-styled Field Rose in Cambridgeshire.

Rosa stylosa   Short-styled Field Rose in Cambridgeshire.

In my quest to photograph all the wild roses in Cambridgeshire (during the summer of 2020), R. stylosa was not an easy species to find.  The recent Flora of Cambridgeshire by Alan Leslie,  points out that it is often recorded as a hybrid with R. canina in scattered sites across the south of the county. Since this is my first season looking at roses,  I was attempting to avoid hybrids and concentrate on learning the basic species first.  The first record for Cambridgeshire from C.C. Babington was redetermined by A.L. Primavesi as R. arvensis x canina so that was another warning that this species might not be straightforward.

As ever, my reference book for this task was the excellent Roses of Great Britain and Ireland , BSBI Handbook no 7 by G.G. Graham and A.L. Primavesi published in 1993, plus a lot of help from Alan Leslie.

R. stylosa, 15Jun2020. Fen Drayton, Cambridgeshire.

Context.

The field guides tend to group the two 'Field Roses' together, R. arvensis and R. stylosa although R. arvensis is one of very few roses in the UK that is not in the section Caninae (unbalanced polyploids). R. arvensis is in section Synstylae whereas  R. stylosa is in the section Caninae and the sub-section Caninae with Dog Roses R. canina and R. caesia. Various papers on the evolutionary history of all these stable species show they shared parents in the past (through hybridisation) and never separated enough to stop hybridisation occurring currently. 

R. stylosa 15Jun2020. Species gets its name from the fused short style.

R. stylosa.

Upper arrow points to the stamen and anthers which are a similar height to the fused style whereas the fused style in R. arvensis is taller being longer than the stamen.

R. arvensis.

Upper arrow points to the fused style of R. arvensis raising the stigma above the level of the stamen and anthers ( second arrow).  The lowest arrows show the conical disc in R. stylosa and the flat disc in R. arvensis although I now think the conical disc is under drawn. The styles in R. stylosa are slightly different lengths so that the stigma cluster is taller in shape than the more domed shape in R. arvensis.

R. stylosa 11Aug2020. Conical disc and fused style starting to come apart.


R. stylosa, 18Oct2020

A late season photo shows the conical disc and the fused style of R. stylosa.

R. arvensis. 20Oct2020

A late season photo shows the flat disc and long fused style of R. arvensis. The hip is typically more soccer than rugby in shape and the pedicle longer. The glandular hairs on the pedicle are almost gone at this stage.

Rosa arvensis is a distinctive species in that it has weak thin stems (often green or purple) that climb through hedges or trees at the edges of woods, often in shady places. R. stylosa is a more typical structure with strong arching stems much like other Dog roses.

R. stylosa. 15Jun2020 

A key feature of both R. arvensis and R. stylosa is that the pedicle has glandular stalked hairs. These hairs are typically shorter than those found in the Downy roses and quite sparse in R. stylosa.  
R. stylosa. 15Jun2020, Bract, pedicle and sepal.

Above photo showing the pedicle below the hypanium with glandular tipped hairs. The sepal is pinnate,  the lobes typically simple without additional side protrusions, although some glandular tipped side protrusions may occur as seen in the photo below on the lower two protrusions.

R.stylosa 11Aug2020, Sepal , very few glandular hairs on margin.

R. tomentella ( was obtusifolia) Bi-pinnate sepals for comparison. Protrusions on protrusions.


Leaves.

R. stylosa 15Jun2020 Leaf with widely spaced leaflets with lowest often reflexed, tapering to an acute apex. Leaflets are 2-2.5 X as long as wide.
R. stylosa 11Aug2020 

R. stylosa 18Aug2020. Reflexed lower leaflets.


R. stylosa 11Aug2020, Leaf stem , petiole and rachis have stalked glandular hairs and pricklets.





R. stylosa 15Jun2020. Leaflet edge is uni-serrate with red tipped hydathodes


R . arvensis leaf edge with temple dome shape.

The leaflet edge is uni-serrate (occasionally bi-serrate) and has the temple domed shape ( convex to concave) to each tip but less pronounced than in R. arvensis with almost straight tip edges on many in the photo of R. stylosa. This shape is seen in some R. canina Dog Rose.  No glandular hairs on the margin in these photo although it can occur in R. stylosa
R. stylosa Leaflet lower surface with white hairs on midrib and secondary veins.


R. stylosa, 15Jun2020 

Deltate prickles on mature stems, a wide base with a triangular shape with either a straight or curved tip.

R. stylosa hybrid 28Jun2020 Orwell.

R. stylosa hybrid 28Jun2020 Orwell.

Although I am avoiding hybrids in an attempt to learn the basic species first, it is easy to get caught out when looking at roses.  The above photo shows the fused stigma and conical disc that made me think this was a R. stylosa. The important message is that you cannot rely on a single feature and the leaves on this plant showed a problem. Other features also did not quite tie up with R. stylosa either.

Hybrid leaflet. 28Jun2020 Orwell.

This leaflet is not correct for a R. stylosa with red tipped glandular hairs on the underside of the leaflet and red-tipped stalked glandular hairs on the leaflet margin.  The edge is multi-serrate and this hybrid is not the common Canina x stylosa (or Stylosa x canina)  and would need expert evaluation. 

R. stylosa 20Oct2020 Hip cut in half to show narrow orifice and thick conical disc.

Conclusion. 

These photos do not show every feature of Short-styled Field Rose ( R. stylosa) but hopefully show some of the important details of this species. The short stalked glandular hairs on the pedicle and the shape of the fused stigma being about the same or below the height of the stamens and the uni-serrate leaf margin are the key features. This is backed up by the sharply pointed dark green leaflets which are well spaced on a petiole and rachis that have stalked glandular hairs. The lowest leaflet pair are often reflexed but not all my photos show this feature well, as it does vary plant to plant. Some versions of the Dog Rose (R. canina) can have the conical disc and similar shape to the style and hybrids are often recorded.

 In some ways R.stylosa fits somewhere between R. arvensis and R. canina but in my first season looking at roses, I think I have achieved some progress in all the species in Cambridgeshire, except R. canina. 

Dog Rose (R. canina) and its hybrids with R. caesia form a very difficult group which I have failed to untangle. The term R.canina agg. might come in useful.


Peter Leonard

28th March 2021

Rampton , Cambridgeshire.



No comments:

Post a Comment