Rough Hawkbit (
Leontodon hispidus) and
Lesser Hawkbit (
Leontodon saxatilis)
As a relatively new convert to botany I thought I would learn to identify the 'yellow dandelions' , since they are everywhere including several species growing in my garden like Smooth Hawksbeard (
Crepis capillaries) and Autumn Hawkbit (
Scorzoneroides autumnalis).
Some groups like
Crepis have proved difficult but the two Leontodon's seemed at first, to be straight forward. My method of learning is based on taking lots of photos and looking out for variation in features that are given as identification clues in the field guides.
Looking at the involucral bracts of the flower head,
hispidus is normally hairy, saxatilis generally has no or few hairs but a couple of photos from Therfield Heath and Devils Ditch broke that pattern and this resulted in a conversation with Dr Alan Leslie. Alan had found several plants that he regarded as hybrids at both Devils Ditch and Chipenham Fen based on the achene pappus having intermediate features. I was keen to take some photographs of these hybrids so a visit was arranged and this resulted in Alan suggesting I put up a display at the BSBI Exhibition meeting.
The following is based on the BSBI exhibit.
1)
Title Page.
2)
Literature.
The
Hybrid Flora of the British Isles by Stace, Preston & Pearman gives a summary of the hybrid, named
Leontodon X vegetus. It was first found as recently as 1945 at Seaton Sluice. Later is was studied by Leontodon specialist R.A. Finch who found it a quite a few other sites across England.
The two species are separated by low F1 fertility when they grow together, however Mr Finch concluded that some 'backcrossed plants occur the the wild, differing from
L. hispidus only in the
pappus of the outer achenes.'
It would appear that the expert botanist takes variation in his stride, whereas the relative newcomer like myself, has a naive expectation that what is written in the field guides has to be true. I am learning that variation is not well covered in the literature. It can be hinted at and a good example being the sentence in Harrap's Wild Flowers, -
Most reliably separated by the clock inner seeds with plumes of long hairs , but outer row of seeds tipped by a collar of pale chaffy scales,....In other words all the other features described are useful but do not rely on them. Mr Harrap choses his words carefully.
Having taken photos at quite a few sites, separating
hispidus from
saxatilis is often straight forward since they look quite different.
L. hispidus is a 'rough' larger plant with a a shaggy flower head and with very hairy bracts and
L. saxatilis has a flower with limited hairs and leaves that stay close to the ground etc. It is always worth checking the common feature that is key to Leontodons , the split hairs normally looked for by bending a leaf over your finger and using a X15 eyepiece. These split hairs are unlike the hooks of Hawkweed Oxtongue, in that they are not hooks but gentle split ends that head off with an angle of about 120degrees between them. Sometimes the splits are tiny occurring at the very tip and occasionally both species have some three pointed hairs ( trifid).
3)
Variation vs hybrids.
Having taken quite a few photos of these two species, initial thought was they are well separated and that hybrids would fall somewhere between them so, without actually doing any real measurements one might come up with the following type of variation concept.
If the variation, is in fact wider and overlapping, then making any firm identification would be very difficult. Alan had told me that Sell noted that
L.hispidus in Eastern Europe has no hairs on its involurcal bracts, so a key feature is highly variable if you travel far enough.
Before we look at hybrids first step is to show some photos of each species pointing out some possible differences that might help in identification.
4)
Lesser Hawkbit (L.saxatilis)
This is a very typical example.
The main feature is the lack of hairs. The stem is quite tapering into the flower head and this is very common in both
L. saxatilis and
L. hispidus. The dark brown and distinct edging to the inner bracts is a distinctive feature of
saxatilis but on some plants can be less distinct and become similar to
hispidus that have vague less distinct brown tips. (This feature is less useful in Spain but seems to work in Ireland.) Outer bracts in saxatilis are tipped red or black. The pale grey under colour banding of the petals show well in this photo but many plants have just yellow petals and occasionally red banding and these features are shared with
L.hispidus .
From the same plant showing the leaf and the low density of hairs. Resolution not quite up to showing that most of these
hairs have split ends. The density of hairs is very variable but a feature I will look more at next year is the length of the hairs which seem longer in
L. saxatilis. The leaves were quite upright at Chippenham Fen as these plants were growing in quite long grass which is contrary to the conventional thought that
saxatilis has leaves that stay low to the ground.
Just to throw in a bit of geographic range this photo was taken in the very west of the Beara Peninsula , West Cork, Ireland and conforms very well to what you might expect a
L.saxatilis to look like in Cambridgeshire with adpressed red tipped bracts, dark brown edging and no hairs.
The picture above shows a more hairy example but it is not uncommon to see this amount of hairs on the bracts. Interesting feature of this plant was the density of hairs on the leaves.
Very hairy. Has the red-based hairs on the midrib showing nicely which is a good feature for
L. saxatilis, although not all leaves have it and some plants do not show this feature at all. I have yet to see a
L. hsipidus with red based hairs on the midrib (very rare?) although they do have the occasional simple red -based hairs present on the leaves.
The shape of the achene being attenuated/short-beaked is noted in Clapham. Tutin & Warburg and is a good feature for the central florets. All achenes have the full pappus of hairs except the very outer row and they have short scales. See photo below.
The outer achenes lie supported by the bracts and can remain long after all the other achenes with pappus hairs have blown away.
The short ring of scales rather than the pappus hairs is the number one ID feature to separate saxatilis from hispidus. These outer achenes can be hard to see until you pull off most of the surrounding seeds. Note they do not have the beaked attenuation and can often be quite curved.
Final shot of Lesser Hawkbit ( L.saxatilis) shows a flower head just after petal stage showing that the outer achene can be seen on the right with its lack of pappus.
5)
Rough Hawkbit ( L.hispidus)
Typically not as neat as Lesser Hawkbit. Yellow petals and without any under petal banding that some examples have. Banding grey/red colour is not a reliable feature between these species.
Often so hairy on the bracts, that you can hardy see the outer bracts are not adpressed and stick out before curving inwards.
This example is unusual in that the outer bracts are adpressed just to show that distinction is not a 100% reliable. However it is hairy, the outer bracts do not have the distinct dark brown edging or the red/black tips. Looks good for
L.hispidus which was confirmed by looking at the seed heads.
Example seed head with
all achenes have the full pappus and the achenes not having the semi-beaked attenuation of
L.saxatilis. Some sterile achenes look very pale.
The achene is thickest at about one third length then tappers down over the next two thirds.
Leaf hairs. Not all plants are this hairy, some have sparse hairs so as usual, the amount of hairs is not a reliable ID feature. The spilt hairs are just about visible in this photo. About 10% or less of the hairs are just simple without a split and if you look hard enough some hairs have three tips (or even 4).
Three tipped hairs have also been found on the leaves of
L.saxatilis.
5)
Candidate Hybrids
Hybrids occur where both species are present based on the theory that the outer achenes have a mixture of short scales and pappus hairs. These sites also display plants that have odd features which could just be variation but I think are more likely to indication of being hybrids.
The first plant I found was at Therefield Heath where a flower stood out as being slightly more orange that any of the
L.hispidus around it. Going over to get a closer look it showed less hairs on the bracts and a slightly thinner flower head shape that normal.
Apart from the petal colour and the narrow shape of the flower head this example has very few hairs compared to nearby
L.hispidus. The inner bracts are not quite normal either with the brown edging looking a bit more like
saxatilis. The outer bracts are sticking out which is often a feature of
L.hispidus. The under petal coloured redish banding occurs in both species. At the time back in 2015, I regarded this as a variation of
L.hispidus but since both species occur at Therfield Heath this could be a hybrid. The stem was not tagged so I could not go back later to check the seeds, so I will never know.
The type of seed head I might have found is shown above. The key feature for hybrids is the mixed short scales and long pappus hairs on the outer achenes. The achenes do not have consistent ends being either like
L.saxatilis with just short scales ( most) or to having a mixture (few). The achenes all appear to be not fertile which lines up well with the Hybrid Flora. The bracts and stem show this plant is towards the hairy end of range indicating
L.hispidus. This photo was taken at Chippenham Fen on a trip with Alan Leslie who had found a mixed population growing close together and plants exhibiting mixed features.
Although it would be expected that most hybrids would have sterile seeds in fact it was not difficult to find seed heads that looked viable. This example has achene ends that fit both species plus the mixed type.
Above photo is an example of flower head that has mixed features , from Chippenham Fen where direct comparison to pure
L.saxatilis and
L. hispidus is possible since they all grow together.
Habitat shot of Chippenham Fen where both species grow together.
6)
Conclusion.
At the BSBI Exhibition I was fortunate to be challenged by no less that Co-author of the
Hybrid Flora, Chris Preston, that none of the secondary features that I was recording to identify between the two species would hold if you travelled across Europe. Having photographed plants in Portugal and Spain, I was forced to say I had to agree, however there is more to learn. If you look hard enough and maybe within Britain and Ireland it might be possible to understand the limits of variation, what are really hybrids and determine the reliability of secondary features.
My reference site for
L.saxatilis which I thought was pure and without variation is at Waterbeach Cemetery. An extra concern was added, when I found two plants that have hybrid features of mixed scales and hairs. Could this mean that the single recognised feature for hybrids is actually not totally reliable? I don't know of any
L. hispidus growing nearby but maybe they do.
I went back the next day to have a closer look and found a flower head on the same plant was not quite as typical for pure saxatilis as one might expect with its red outer bracts and slightly larger size. Maybe it is a hybrid after all and my pure site is not as pure as I believed?
Finally a few preliminary notes on features and problems.
Peter Leonard. Rampton, Cambridgeshire. 2nd December 2017
