Hieracium aviicola Many-toothed Hawkweed

 Hieracium aviicola   Many-toothed Hawkweed    Devils Ditch. Newmarket Heath.

Hawkweed on Devils Ditch, Newmarket Heath, Cambridgeshire.

There is a new Hawkweed book, Hawkweeds of South-East England by Mike Shaw recently published by the BSBI. It builds on the previous work by Vincent Jones with the ground breaking Yorkshire Hawkweeds published by the Yorkshire Natualists Union, now out of print.  Between these two books a large number of the hawkweeds in England can now be identified in theory. In practice the identification of Hawkweeds remains difficult. I had an advantage when shown this Hawkweed, in that I was with Alan Leslie (who has recently written the new Flora of Cambridgeshire, RHS 2019) and he knew what species it was. He had seen it in the past at this site and also knew that Peter Sell ( Co-author of Flora of Great Britain and Ireland, vols 1-5) had been involved in the original confirmation. Peter Sell was a great enthusiast and expert on Hawkweeds. He grew many Hawkweed species in the Cambridge Botanic Gardens to study them in detail.

The question is could I have, as a 'Hawkweed beginner' identified it myself, based on the photos I had taken?

Both books on Hawkweeds have keys and both books cover H. aviicola. I used the South-East England book as a test.

The first item in any Hawkweed identification is to check whether the plant has basal leaves when in flower and then the number of stem leaves. The photo above shows the basal leaves are certainly present and in full health. The single stem has three stem leaves and a fourth that might be regarded as a inflorescence bract. There is also a higher bract. The count of stem leaves plus inflorescence bracts going up one stem path is important, as the first question in the Key is are there more or less than eight.

We have five (maybe six) here.

The other factor is: Does the plant look well, robust and undamaged? - It does. 

Next key question is: Are the leaves covered in glandular hairs to exclude a group called Amplexicaulia?

Basal leaves.

These basal leaves have a few white hairs mainly along the margin and very few on the lamina surface.

So not Amplexicaulia.  Note the  basal leaves have quite a long petiole and have quite short teeth.

The next question relates to number of stem leaves. 

Stem leaves 0-1(2) : basal leaves numerous  in which case go to Hieracium group.

Stem leaves 2-8 : basal leaves usually few in which case go to group Oreadea or Vulgata.

We have about 5 stem leaves/bracts so looks like we can exclude Hieracium group. Also basal leaves are few but this seems a bit vague and a number would be better.

Oreadea has phyllaries that have predominant eglandular hairs whereas Vulgata has a mixture of eglandular and glandular hairs but glandular hairs usually predominant.

Glandular hairs predominant.

Phyllaries clearly are covered in glandular hairs so it looks as if the Hawkweed we have here is in the Vulgata group.

We hit two problems at this stage, one is that there are a lot of species in the Vulgata group and some are grouped together as aggregates as they are so similar. This is where the Vulgata key in the South-East England book fails, as its key does not include the aggregate groups ( H. maculate agg. , H. diaphanous agg., and  H. acuminatum agg.). These groups are covered but not linked by the key.

Fortunately in the Yorkshire book, Vulgata key does include aggregate groups (on page 101). 

I now use the Yorkshire book and its key.

Leaves unspotted takes us onto phyllaries with predominant glandular hairs and then we get into real detail. 

The next key split is dependent on the density of stellate hairs on the phyllaries. The photo above does show some stellate hairs but more magnification is needed.

Stellate hairs ( I normally call these cobwebby hairs)

Stellate hairs are certainly present especially on the margins of the phyllaries which moves us onto

the next question. Do the upper stem leaves have stellate hairs present on the lower surface? 

Lots of simple white hairs but no sign of any stellate hairs on the lower surface.

At this point the size of the teeth on the leaves come in and section 9 of the key gives following choice:-

Leaves entire to denticulate or with small teeth.                                            10

Leaves obviously dentate, often with mammiform teeth.                               H. acuminate agg.

-entire is lacking teeth, 

-denticulate means with regular small fine patent teeth, evenly spaced.

-dentate  means with large more or less patent teeth.

-mammiform with more or less rounded teeth which can vary in size and are pointed at the tip.

First problem here is what leaves are they referring to , basal leaves or stem leaves. I assume stem leaves. The basal leaves have quite small teeth but the stem leaves have quite pronounced teeth.

I would regard the teeth on the above stem leaf is large and pointed so I think we have arrived at 

H. acuminate agg. Having said that, there was a population of about 20 plants and there was quite a lot of variation in teeth size.

Whether we should just stop at H. acuminatum agg. rather than try and spit this group further is a good question. We all know that plants within a species can vary considerably in various features but strangely many Hieracium 'species' apparently have very little variation and this is some ways justifies their status as species.  It would seem we have been using quite tiny changes to arrive at H. acuminate agg.  The justification for continuing to split further would have to be based on consistent features over a geographical range. This would appear to be the case for these vulgata hawkweeds, which is the case of H. aviicola are widely recorded across England and Wales.

 These species reproduce by selfing, i.e. producing clones.  As a hawkweed beginner, all I can do is see how far I can go using these new books and see if I can work out  if the description and photos I have taken tie up with the description in the literature. 

The following species make up the H. acuminatum agg. :-

(H. acuminatum)    

H. consociatum

H. argillaceum

H. aviicola

H. nemophilum

H. chlorophyllum

H. festinum

H. cheriense

No Key is provided in the South-East England book but the Yorkshire book does cover the five species seen in Yorkshire, which includes H. aviicola. The leaf shape and dentition seems to be the main difference.

Basal leaf shows quite limited teeth 

Lower stem leaves seem to vary in the amount of teeth depending on what plant you look at.

This example has very limited teeth but is does vary from leaf to leaf.

Mid-stem leaf  July 2020 Devils Ditch. Newmarket.

A different plant in the same population has teeth that are very narrow and quite long.

The key talks about the teeth being longer than 6mm ( up to 10mm on stem leaves) or less than 6mm.

I think the plants at the Devils Ditch are typically below 6mm which leaves H. argillaceum, H. aviicola, and H. nemophilum.  At this point the very first photo shows the stem leaves gradually decreasing in size upwards which fits with H. aviicola. Result, happiness!- but the differences between these three species is very small in the terms of the key descriptions. 

In practice I looked at other features not in the key, to confirm the identification by reading the notes and photos about H. aviicola is both books.  The leaves tend to taper at both ends which fits in with the choice of all three species in the sub-group. 'The inflorescence with long lower branches from the leaf axils and with the lower peduncles making a wide angle with the stem and the upper being more or less erect, giving a large, broad panicle' fits well with H. aviicola and this is apparent in the structure seen in the very first photo and the photo below. However I lack experience of the other two species.

Styles are stated to be yellow in the Yorkshire and the South-East England books, so that matches with photo below.

Yellow stigma

In truth, without knowing what the species at the start ( thanks to Alan Leslie),   I would have struggled, in this final stage to get to the right result.  In reality you would need a lot of hard earned practice to get the expertise required.  This is hard to achieve but both books give sites where you can observe the various species and that it probably the only way to improve one's knowledge.  Both these regional books have great photos of example plants and these give as much insight as the keys, when you get close to the solution. Sometimes keys fail however and then a more multi-feature approach is needed.

 Early days but I have learnt a bit more on the detail needed to identify these difficult Hawkweeds. I suspect that this Vulgata group are not the easiest to make a start with. Without the books by Vince Jones and Mike Shaw I would not stand a chance. 

Resources:-

Hawkweeds of South-East England by Mike Shaw, BSBI Handbook No 20.

Yorkshire Hawkweeds by Vincent Jones , Yorkshire Naturalists' Union.

Flora of Great Britain and Ireland, Vol 4 by Peter Sell and Gina Murrell.   

Pedicles have stellate and glandular hairs.  7th July 2020

Peter Leonard

Rampton, Cambridgeshire.

22nd January 2021