Acicles

 Acicles, Prickles and Stalked glands in Wild Roses.  Photos and thoughts.

Rosa rubiginosa showing pedicle acicles and stalked glandular hairs.

Since June I have been looking at Roses. A difficult group of species which often hybridise.

As a beginner I was advised to ignore hybrids, as even separating the species is hard enough for a first year. Anything which did not fit the species description in the BSBI Handbook no7, Roses of Great Britain and Ireland, was at first given the 'walk on by' treatment. Eventually, as confidence grew,  a guess was made to the possible parents of a hybrid plant. An example was a possible hybrid between Rosa micrantha ( Small-flowered Sweet Briar) and Rosa rubignosa ( Sweet Briar) which was somewhat dependent on the presence or absence of Acicles.

This raises the question of what actually does an acicle look like?   How do you separate an acicle from a stalked glandular hair or a straight prickle?  The term acicle is applied to the rigid version on the main stems and also to the soft versions seen on the pedicle and hypanthium and this can cause some confusion.

The handbook treats acicles as a type of prickle on the stems, however in the description of Rosa rubiginosa it describes the pedicles as glandular-hispid, the glands often mixed with small acicles.

The Rose handbook description for an acicle is :-  In a few species such as R. pimpinellifolia the larger prickles may be interspersed with much smaller ones called acicles. These are often straighter than the large prickles, and may come in all sizes down to what appear to be stiff bristles.  However unlike a true bristle ( or stiff hair), acicles always taper to a point from a broad base. Occasionally acicles are gland-tipped.

P. pimpinellifolia  All prickles or are there acicles as well?

Another definition from CTW is :- Very slender prickles or stiff bristles, not stout-based, sometimes gland-tipped. Stace defines acicle as - a slender prickle with scarcely widened base.

In practice these definitions hide the fact that stalked-glandular hairs, acicles and straight prickles could be said to form a continuum. 

Location.

The acicles can be present on the pedicle/hypanthium and the flowering stems although the stem version are hard and stiff whereas the versions on the pedicle are flexible.  Maybe separate names could be used for the types of 'hair' found on the pedicle/hypanthium vs stem.

R. rubiginosa hypanthium and pedicle (flower stem).This photo shows the longer non glandular acicles and the shorter glandular stalked hairs.

The above photo of R. rubiginosa clearly shows two types of hair. 

Glandular hair. Some are clearly stalked glandular hairs with the gland being of a size that forms a large ball whose diameter is several times that of the diameter of the hair tip, on which it rests.  

Acicle. The second type of 'hair' is generally longer, has a thicker tapering body and usually ends without a glandular tip.  I have regarded these as acicles. Occasionally these acicles have glandular tips but these are often not balls but just darkened ends. One feature is that the very base of these acicles is not enlarged by any great extent unlike a prickle. 

Since acicles are a feature of R. rubiginosa and are not seen on R. micrantha or the Downy roses like R. sherardii it might be worth looking at examples of pedicle/hypanthium hairs on these species.

R. sherardii  23rd September, West Cork.

The point of this photo is to show that no acicles are present which is what you would expect, but that the length of the stalked glandular hairs can include very long ones. Length cannot be used as a determining feature in distinguishing acicles from glandular hairs.

R. micrantha, 12th June, Cambridge.

 The above photo shows Small-flowered Sweet Briar with stalked glandular hairs and no acicles which conforms to the expected species description. These glandular hairs do not appear insect friendly.

R. rubiginosa. 14th October , Croydon.

The glandular tips are deteriorating rapidly turning white at this time when the fruit are going soft.  This photo shows how difficult it can be to distinguish between the stalked glandular hairs and the acicles which can be the same length. The lower right 'hair' had a large ball of sticky chemical whereas the one going left looks as if it just terminates in a point and is therefore a acicle.  The complication is that glandular hairs can lose their glandular tips and acicles can occasionally have glandular tips with a ball shaped gland on.

R. rubiginosa 14th Oct  Croydon.

A feature of R. rubiginosa is the unequal prickles on the stems.     This photo shows the variation of dense prickles, many of which are thin and narrow pointed and might be regarded as acicles. The more typical curved prickle is shown in the next photo which is part of the same plant. This variation in the shape of the prickles is typical of rubiginosa. 

 

R. rubiginosa 14th Oct Croydon showing more typical shaped prickles.

R. rubiginosa , stem just below pedicles

The descriptions in the literature do not clearly differentiate between an acicle and a straight thin prickle. I would regard the prickles on the main stem as thin prickles since they have a elliptical base. Strangely some have a tiny glandular tip. This is an example of the intermediate characteristics that  occur. The conflict in the description about the base being either wide or not wide, from the Rose handbook, CWT and Stace, adds to the confusion. My thought is that it's the shape of the base rather than the width, that to me seems to separate prickles from acicles.

14th Oct Hybrid R. micrantha/rubiginosa 

The above photo shows an acicle with three stalked glandular hairs. The glandular tips are deteriorating at this late stage. All have slightly wider bases but this is limited compared with a true prickle. 

 

Example of accicle with round base on stem just below pedicles.

Stalked glandular hair on hypanthium ( R. tomentosa)

Intermediate in that the base appears somewhat elliptical but tiny glandular tips are present.

A straight prickle, based on its elliptical base. 

Fig 1. Possible difference between stalked glandular hairs, acicles and narrow straight prickles.

 Length is variable although acicles are often longer than stalked glandular hairs on the pedicle/hypthanium. Bases can be smaller than shown as proportions are for short versions.

Glandular hairs sometimes lack the glandular tip and acicles occasionally have glandular tips. Surprisingly even straight prickles have been seen with glandular tips on one occasion so all three types are not absolute in their features. Approximate colouring is late season, hairs and acicles are green at flowering time. Prickles are rigid when mature, acicles and stalked glandular hairs remain flexible on the pedicle.  Acicles have a tapering tip, sometimes darker or occasionally a glandular ball which might be slightly smaller than usually seen on adjacent stalked glandular hairs.  Since no absolute difference is 100%, check more candidates on the plant to determine the presence of acicles.  

With roses, no rule is 100%, so careful consideration has to be given to the complete range of features.  

I have avoided using the term 'pricklet' as in the handbook it is used to describe the smaller prickles that occur on the petiole and rachis ( leaf stems).  

Pricklet on rachis

Another term used is bristle, which is used in place of acicle in Harrap's wild flowers.

Peter Leonard   Rampton     18th October 2020

Please comment if you can add anything to this possible interpretation or let me know if I have misunderstood the literature.  The rose season is just about over so it will be next year before I can learn more about this difficult group. 

 

Reference:-  Roses of Great Britain and Ireland by G.G. Graham and A.L. Primvesi, BSBI Handbook No 7.

Leaf edges in Cambridgeshire Roses

Leaf edges in Cambridgeshire Roses.



On the 3rd June I had zero knowledge of roses. A chance encounter with Rosa micrantha (when looking at Crested Cow-wheat), initiated a quest to see and photograph all the possible rose species to be found in Cambridgeshire.

The main problem with wild roses is they all hybridise with each other and I took good advice to ignore hybrids, at least to start with.  I looked for pure examples of each species, based on the principle that I need to learn the features of each basic species, before one could even consider examining hybrid plants. This involved rejecting examples which did not conform exactly to the handbook description.

I ordered Sell and and Murrell Volume 2 which arrived on the 5th June. This volume contained somewhat disturbing news, quote ' We support John Lindley's remark of two hundred years ago that the study of Roses has been so detailed that one can no longer distinguish species. They are in a taxonomic and nomenclatural mess. All we have been able to do is follow Graham & Primavesi's (1998) Roses of Great Britain for species and hybrids, but we believe that this is a dumbing-down which produces aggregates that could be ecological and geographic non-sense'.

Roses of Great Britain and Ireland, BSBI Handbook No7 by Graham and Primavesi would appear to be a very good starting point despite the rather negative comments by Mr Sell.
Over the summer I have managed to photograph the possible species to be found in Cambridgeshire using the handbook No7 as a guide, in an attempt to find 'pure' non-hybrid examples. Actually all the roses are derived from hybrids and what are regarded as species are just stabilised and widespread plants that share the same features. The BSBI handbook is well laid out, has good line drawings and is concise covering species and hybrids and remains the essential reference text. More recent Dutch work still uses much of its content.

This blog shows leaflet edges of the species and compares them with the stated description in the handbook, as either uni-serrate, bi-serrate or multi-serrate.

Handbook descriptions are stated for each species and the photos compared to see if they agree with that description. Definitions from handbook :-

A) A Uniserrate  leaflet has sharp teeth, all more or less the same size.

B) Biserrate is defined as having large teeth, from the lower side of each of which a single smaller tooth arises.

C) A Multiserrate leaflet has large teeth, on the lower side of which, and sometimes also on the upper side, two or more smaller teeth arise, these secondary teeth being usually gland-tipped. This type is not as well defined as the previous ones, because in some cases the secondary teeth are little more than rounded protuberances tipped with glands, and the larger primary teeth are sometimes not noticeably sharp-pointed.


One immediate problem when looking at leaf edges is that there is variation even on a single leaflet, which for example may have uni-serrate teeth on one part and bi-serrate on another.

1) R. arvensis Field Rose

Temple dome shape with base convex and concave point.

R arvensis leaflet tip showing dome shape teeth with the tips having a hydathode.

Described as crenate-serrate. Crenate means rounded. The hydathode is a hard red tip, not glandular.

Dome shape only present towards tip of leaflet.

This is not a clear cut difference but pure R. arvensis tends to have the dome shaped teeth at least on the sides near the tip. Other species share this temple dome shape but the convex base is often not quite as pronounced. Burnet Rose also has these temple dome shaped teeth but it does not occur wild in Cambridgeshire. Some Dog Rose and hybrids also show this dome shape. 

A R. arvensis  that does not show this shape might well not be pure. Those with occasional stalked glands would suggest some influence of some other species. Note also the example above has some bi-serrate sections which are less temple dome shaped.

R. tomentosa

Dog Rose

2) R. stylosa Short-styled Rose

Described as uniserrate. R. stylosa  shares the dome shaped teeth but not as perfect as in R. arvensis.

R. stylosa showing Uni-serrate edges

Hydrathodes only , no stalked glandular hairs should be present.

3) R. Canina agg.  Dog Rose

Example of a Dog Rose with red tips ( hydathodes) only without any glandular tips. The secondary tips when probed were hard and did not show the normal soft sticky balls that glandular tips have. They seem to be hydathodes rather than glandular hairs. This leaf edge could be regarded as bi-serrate with alternate main teeth and secondary smaller teeth.

Example of a Dog Rose ( possibly a hybrid with R. stylosa) with red tips plus some stalked glandular hairs. This edge might actually fit the description of a bi-serrate edge with its primary teeth and smaller secondary teeth..
Dog Rose is an aggregate of several different variations. The additional problem in Cambridgeshire, is that the Northern Dog Rose R. cassia has hybridised with R. canina and these hybrids are the most common (but variable) plants to be found.

Dog Rose showing that different parts of a leaf may have a different types of edge.

R. canina can have uni, bi and multi serrate leaf edges depending on type although so far I have not found a example with a multi-serrate edge ( group Dumales)

4) R. obtusifolia now called tomentela  Round-leaved Rose.

Described as finely biserrate with numerous small, reddish-brown glands on the teeth.
The glands tend to have formed their own tips giving a multi-serrate appearance but note the glandular tips tend to occur on only one side of the main teeth. This might just about pull the description back to being biserrate. Tricky as the clear sides main tooth edge has a single glandular tip on three of the teeth seen in this photo against only two which have no secondary teeth. Secondary teeth, number two rather than the single tooth as suggested in the description of bi-serrate. I think these definitions are starting to struggle with this leaf edge. I would call this multi-serrate because the glandular hairs are generating tips of their own and not just formed straight onto the edge. 

This example has glands on the underside but this feature is lacking in several of the Cambridgeshire sites.

R. obtusifolia 22nd June Burton End, Cambridgeshire 

This example has very round leaflets but this does not guarantee a obtustifolia as hybrids can have same rounded shape. The edge appears very spiky as the teeth are quite narrow.

R obtusifolia.  5th July 2020 Gamlingay Wood.

The small leaflets have some tendency towards a bi-serrate edge but it is not consistent. Leaflet shape not quite so round but still typical, with lots of overlap and hairs on both sides.

R. obtusifolia except middle hybrid leaf.  4th August Gamlingay Wood

R. obtusifolia except middle hybrid leaf.  4th August Gamlingay Wood

Many plants are hybrids Rosa canina x obtusifolia ( R. x dumetorum) so it is quite hard to find examples that really fit with Round-leaved Rose 100%.  The leaflets overlapping is probably more important than the rounded shape which is present in some of the hybrids. R. obtusifolia leaflets tend to have a dark shinny green surface with at least some white hairs on upper surface although canina agg. can have some white hairs on upper surface but normally limited to near the mid-rib. Not an easy species to nail down and not common at all in Cambridgeshire. Most of the plants at Gamlingay Wood were not 100% conforming to the required feature set of Round-leaved Rose, but a couple of plants on the east edge did seem to fit.

5) R. rubiginosa Sweet Briar

Described as strongly glandular-biserrate.  This photo above does show a bi-serrate edge. A second leaf photo below does show this with primary teeth and slightly smaller secondary teeth. It is certainly strongly glandular.

Glandular hairs are stalked and often do not form tips on leaf edge.

The bi-serrate edge  is clear  with many glandular hairs on the edge which rarely form a point of their own. R micrantha seems to have glandular hairs that form tips but at a low density, but a much larger sample of plants would be needed to see if this feature is consistent and it's a very subtle difference given the leaf to leaf variation. Whereas R. rubiginosa seems to have a bi-serrate edge, R. micrantha seems to lack this being multi-serrate. Probably not a reliable difference but worth looking for.

6) R. micrantha Small-flowered Sweet Briar

Described as glandular multi serrate. I would agree as the glandular hairs are often forming their own tips  but the quantity of glandular hairs is quite low with typical just one on the leading edge and two on the trailing edge.

R. micrantha showing glandular hairs on tips.

R micrantha showing sparse glandular tips without stalks.

7) R. tomentosa  Harsh Downy Rose

Described as irregularly biserrate.
Underside of leaflet very hairy with white matted hairs. Edge has red tipped hydathodes on the teeth tips and the teeth sides have short stalked glandular hairs which are mostly formed on small teeth of their own. Zero to a maximum of three glands per trailing edge tooth side. The leading or clear edge of each primary tooth in this case has no glandular hairs.
 Biserrate is defined as having large teeth, from the lower side of each of which a single smaller tooth arises. It is a fine distinction to multi-serrate. In this example the primary large teeth are dominant whereas the next species examples of multi-serrate edges, the secondary glandular tips make the primary teeth less dominant.
This is partly down to tomentosa having fewer glandular tips.
Note the lack of tiny glandular on the underside leaf surface which are hard to see at the best of times but appear to be missing in many R. tomentosa in Cambridge. Sometimes a few leaves have the tiny stalked glands whereas as many lack them on the same plant. Due to the hairs on both sides of the leaflet it can be hard to see the margin clearly but in conclusion I would say the leaf edge is bi-serrate to multi-serrate so irregularly biserrate is not far off.

8) R. sherardii  Sherard's Downy Rose.

Described as glandular-multiserrate.
Red hydathode tips as usual plus glandular short stalked hairs on tiny teeth (most of the time) do give a multi serrate look to the leaflet edge.   Between one and four glandular hairs per main tooth side. Glandular tip quite variable in size. A rather messy edge.

R. sherardii  1st September 20  Fourwentways. Cambridgeshire

9) R. agrestis Small-leaved Rose

Described as glandular-multiserrate.  The tips have the usual red hydathodes  and short stalked glandular hairs which are on the sides of the teeth without forming a separate tip of their own.  One to four glands occur on each side of the tooth. In some ways the leaflet edge is uni-serrate with additional glands as these glands only have formed on tiny teeth of their own to a very limited extent.
Without this level of magnification the leaflet edge would look glandular multi serrate. No clear edge of the main teeth appears with secondary glandular teeth on both sides although the shape indicates the right hand edge is the clear one which on average also has less glandular hairs. The leaflet tip will be to the right, indicated by the clear edge being on the right hand side.

R. agrestis 22nd August 2020 

Conclusion.

The descriptions for bi- and multi serrate  are tricky. This is recognised in the description on Multi-serrate in the handbook and I suppose the authors were somewhat constrained by previous work.
The think the main problem is due to the glandular hairs either just being on the leaflet edge or forming a point on their own. If the point is large you get the multi-serrate appearance even if the basic leaf edge is uni-serrate or bi-serrate. The example above for R. agrestis has a basic uni-serrate edge with all primary teeth the same size. The glandular hairs are mainly not forming any tips and the few that do are tiny. Because the glands are quite large in the field this edge would look multi-serrate but when enlarged and looked at in this level of detail a better description might be uni-serrate with additional glands. And that is before we consider variation.

I can't say I have found any new insights into separating these species but I am now at least more aware of the current descriptions and will pay more attention next season. Hydrathodes are solid whereas glandular hairs have a ball of sticky stuff at the tip but as the glandular hair ages it will lose some of its stickiness so that it can be hard to tell them apart unless examined under a microscope. As ever, you can't name a rose by only looking at its leaves, as all features have to be examined.

Peter Leonard
23rd August 2020
Rampton
Cambridgeshire.

Update  More pictures of R. micrantha.

R.  micrantha  28th October 2020. Castle Camps, Cambs.

R. micrantha  20 Oct 20 Langley Wood, Cambs