Identification of Roses, Leaf stipules.

Identification of Wild Roses, Leaf stipules. Based on new research by Tony O'Mahony.

Leaf of Rosa agrestis showing stipule.

In a recent major article by Tony O'Mahony in the Irish BSBI bulletin (ref 1), he found that Dog Roses in the subsection Caninae ( Canina, caesia, corymbifera and stylosa etc.), leaf stipules have a different gland type to that of other groups ( Rubiginosa and Vestitae.).

  His article covers many other new features but here, I thought I would illustrate the stipule gland feature, as it has been found to work well in Cambridgshire.

Warning. Dog Roses are a difficult group with features that not easy to separate into what are now regarded as 'species'. Recently British and European Dog Rose species have been aligned ( ref. 2) resulting in R. canina being split into three species, R. canina, R. corymbifera and R. squarrosa. Also the Northern Dog Rose R. caesia has been split into R. caesia and R. dumalis/vosagiaca. Unfortunately an updated BSBI Handbook has not appeared yet although I hear one is being written, so the BSBI Handbook No7 by Graham and Primavesi (ref. 3)is still the best source of information. Good though it is, it is now showing its age. New features that Tony O'Mahony has found are not covered.

The Species Problem.  Roses as a group do not fit into neat species. What now have been decided to be  'species' are hybrids that arose in the distant past from unknown parents and became stable and spread as ice ages came and went. Although 'stable' the evolutional splits and regroupings never reached the stage where different 'species' could not freely hybridise. In more recent times, although these old established 'species' are widespread, any local groupings of different 'species' will hybridise and sometimes produce viable offspring. The problem is particularly bad with the Group Caninae (Dog Roses) with their strange unbalanced combining of the parents genes (canina-type meiosis) plus frequent hybridisation. Reciculate lineages in evolution cause problems as most genetic analysis  assumes a branching tree of life to generate the relationships between species (Phenograms).  

As an amateur botanist without any formal training, I try and look at as many features of a rose as I can cope with and see if they all fit the somewhat basic descriptions in the handbook. Some plants fit well but many have aberrant features, which indicate they are not quite right for a perfect example of that species. The additional feature of stipule glands can help to confirm a good fit but can also show a Dog rose which was thought to be a straight forward R. canina but is in fact hiding some genes from, say a Sweet Briar. The stipule glands are however a useful identification tool to add to the range of feature that should be considered.

The New Feature.

Tony O'Mahony spotted that Dog Roses ( Subgroup Caninae) have stipule glands that are not round but elongated and also are feebly attached and therefore quickly detach leaving older leaves to have none left on the margin. Often these glands are well spaced on the margin and forward pointing.

Subsections Vestige ( R. mollis, sherardii, tomentosa, villosa) and Rubiginosa ( R. agrestis, micrantha, rubiginosa) have have stipule margin glands on stout stipes ( stalks) , the stipes are patent and permanently attached. Each gland is round in shape and when fresh, full of volatile oils, often red in colour. Strangely they often have a larger one, then a smaller, then a larger one along the margin and can be quite dense.

A) Dog Roses.

Rosa canina, close up of elongated glands on stipule margin near the tip.

Rosa canina. Rampton 31Jul23. Elongated glands and also missing ones which have got detached.

Note that the elongated glands on the stipule margin are different from the petiole glands (leaf stalk) which are stalked and round tipped.

R. corymbifera. Even when dried out the glandular tips of this Dog rose are clearly elongated and in this example, on forward pointing tips. 27th July 23. Cambridgeshire.

Dog Rose. R. canina . 7Jun23 Devils Ditch, Cambridgeshire

The photo above shows elongated glands which are mainly forward pointing and also sections of the stipule margin that have lost their glands even at this time in June. 

R. canina with possibly some caesia in it. Allendale, 21Jul23 

Above photo included to give a bit more geographic range ( Northumberland) to these photos. A dog rose that had mixed features of canina and caesia and therefore regarded as a hybrid.   It does show forward pointing glands, which even though dried are elongated, although the smaller ones do appear to be more rounded. It is possible that this particular rose has a more complex history and is not 100% a dog rose. It would seem that the Dog Roses can also have the big, small, big gland pattern but what that means is unclear.

Another canina/caesia hybrid, Fen Drayton, Cambridgeshire, 

Clearly elongated glands but not as forward pointing as one might expect. Interestedly the larger elongated glands are interspersed with smaller sessile glands. This does seem to occur in some examples of Dog Rose.

R. stylosa. slightly dried but still elongated and forward pointing.
25 Jul23 Comberton , Cambridgeshire.

It is interesting that although R. stylosa is held within the Subsection Caninae it is often regarded as not being a Dog Rose yet it still displays the elongated forward pointing glands. It does show some variation in size with the big, small, big pattern, seen in the non Dog rose groups but also in some Dog Roses. 

B) Non Dog Roses.

R. rubiginosa. Fresh round glands on short stalks, patent not pointing forward.
25th July 23 Comberton, Cambridgeshire.

This example shows the big, small, big alternate sized glands, the smaller being sessile.

R. sherardii, 23 Jul 23. A11 junction near Duxford.

 A non Dog Rose in that rounded glands, not forward pointing, dense along margin and displaying the big, small, big pattern. 

Conclusion.

It would appear that there is a difference between Dog roses and non Dog roses when it comes to stipule gland shape. The forward pointing and big, small, big features seem more random. What works in County Cork seems to work here in Cambridgeshire. 

There are problems in that the Dog roses have often lost all their  glands but usually it is possible to find a new leaf on a late non flowering shoot which may have glands left. The gland shape can be seen with a X10 or X15 magnifier.  The paper by Tony O'Mahony is linked below and he has to be congratulated on highlighting this new feature.  

Ref 1,  Irish BSBI News No 33 Page 5  by Tony O'Mahony

https://bsbi.org/wp-content/uploads/dlm_uploads/2023/05/IBN-2023-V2.pdf

Ref 2, 

Dog-roses (Rosa sect. Caninae): towards a consensus taxonomy, Piet Bakker, Bert Maes, Roger Maskew, Clive Stace.

https://britishandirishbotany.org/index.php/bib/article/view/10

Ref 3, Roses of Great Britain and Ireland by G.G. Graham and A.L. Primavesi BSBI Handbook No 7 1993

Peter Leonard

Rampton, Cambridgeshire

10 Aug 2023

Update 29th August 2023.

Roses are never going to be easy and today in Hayley Wood we found a rose that would appear to be a dog rose with no glands on the pedicle and might fit the group Dumales/ R. squarosa, but had round glands on the leaf stipule. This and another similar plant nearby seems to break the rule and can only wonder what this means in terms of its parents. This combination of Dog Rose features and round glands on the leaf stipule is not common as several hundred roses up to this point had conformed to the suggestions by Tony O'Mahony. I can only assume this is down to a more complex history with some hybridisation to a non-caninia type rose. A few photos follow.

Dog Rose, R. squarrosa Hayley Wood. 29th Aug 23

A rule breaking example of a Dog Rose showing round stipule glands.

Dog Rose , Hayley Wood , with round leaf stipule glands. The hip is more rounded than typical Dog Roses found in Hayley Wood which might indicate a more complex history.

Dog Rose at Hayley Wood, with round leaf stipules glands. The orifice is narrow as expected and the disc almost flat to slightly convex. Many of the Dog roses in Hayley Wood have a much more convex disc.