It’s a family affair: Linaria arvensis? (toadflax)

 

Leaving the question mark to one side for the moment, let’s deal with the names. The toad is an animal I left till the end of the last post, and it’s another derogatory name-calling thing – it’s a good job plants can’t argue back or we’d be deafened on any country walk.  Grigson says ‘toadflax’ (as a name for Linaria vulgaris) came from William Turner’s  1548 translation of the German Krottenflachs – a ‘wild, useless flax, a flax for toads’. Linaria means ‘like the linen or flax plant’, and arvensis just means ‘of the fields’.

Linaria in a corner of the garden

It is a small (a few millimetres long) and relatively insignificant flower – one French website says it passes almost unnoticed due to the slenderness of its stem and the paleness of its flowers – but my efforts to identify it made me learn about many different things: recent DNA research, the trustworthiness of both books and the internet, the way evolution is ongoing, a puzzle for the great Swedish botanist Linnaeus, and the hidden presence of anti-Darwin creationists. So the length of this post is out of all proportion to that of the flowers. So much so, in fact, that I’ve decided to split it into two parts, with the next one in a couple of days.

I’ve had problems with the identification of this plant – and I’m far from the only one.  When I saw the leaves in spring I thought it was a spurge (Euphorbia, probably cyparissias) because of the pinkish stems and whorls of slender greyish leaves.  Then the flowers appeared a few weeks ago and they were clearly snapdragon-like, apparently one of the Scrophulariaceae (figwort) family. The flowers most resemble toadflax – the Linaria genus – but I couldn’t pin it down to any one species,  and then I found that Linaria has been reallocated lock stock and barrel to another family, Plantaginaceae, the plantains, which it doesn’t resemble at all.  What’s going on?

 

Whole Linaria plant measured on the kitchen table – leaves more like spurge than toadflax

This is a result of new DNA research updating the old classification which had been based on morphology, or appearance.  Studies which analysed DNA sequences of these plants about ten years ago showed that the Scrophulariaceae family was in fact composed of five distinct lineages (monophyletic groups is the technical term), and the largest number have been told to go and join the plantains.  ‘Ah’ said Chaiselongue insightfully, ‘they were adopted, and they’ve been told to go back to their natural parents’. That’s more or less it, and the genera leaving their adopted home and arriving chez  Plantain  include Antirrhinum (snapdragons proper), Anarrhinum (similar), Linaria (toadflaxes), Cymbalaria (ivy-leafed toadflaxes), Digitalis (foxgloves) and Veronica (speedwells).

This is a cautionary tale for amateur botanists – like me – because the flower guides are not properly updated. My main references (Wild Flowers of the Mediterranean by Blamey and Grey-Wilson [2008], and La nature méditerranéenne by Martin [2011]) were published after this revision of families but don’t show it.  Neither does the tela botanica website. How should you check? The best source to go to is the one used by professionals: the Plant List – http://www.theplantlist.org – which is a project jointly led by Kew Gardens and the Missouri Botanic Gardens to produce ‘a working list of all plant species’. All details for these sources are in the ‘Resources’ section of this blog – see the tab at the top.

Linaria flower measured, showing spur (scale in cm/mm)

The need for caution doesn’t stop there. The flower colour of my plant is like L. repens, but the small size of the flowers is more like L. arvensis or micrantha; the spur, a characteristic backward projection from the lower petals, is short and straight like L. simplex, but those flowers are yellow. Checking names and photos between books and websites such as the above and also the useful http://www.florealpes.com, I found that several sites which use photos uploaded by the public have many errors – well, there were huge differences between the pictures, sometimes on the same site, and they can’t all be right. These sites are evidently not edited or supervised, and any information is only as good as the last uploading amateur.  In another example of disagreement, the Wikipedia  entry says there are 100 species of Linaria, but the Plant List gives only 29 accepted species, among no less than  642 commonly used species names, most awaiting scrutiny. Linaria is a confusing genus.

There are reasons for this, and as I used to tell my students (I was a psychology lecturer) confusion is an advance, a stage in learning: first you think you know, then you get confused, then you know better, or at least see the limits of your knowledge.  Digging around on Google I found several research papers on Linaria which pointed out how easily different species hybridise, or cross, with each other – aided in part by the fact that the plants are not self-fertile, they have to cross with another individual (a feature noted in plants by Darwin as favouring  variety and hence evolution).  In 1948 the botanist Dilleman went as far as to call the whole genus ‘promiscuous’, after noting in the Paris Botanical Gardens that L. purpurea hybridised with members of any neighbouring Linaria species.  ‘How does this happen’, you may ask, ‘I thought species couldn’t interbreed, isn’t that the whole definition of a species?’

Well yes, it is part of the definition: that’s what happens eventually as species diverge. This crossing between species is a sign that Linaria is in the middle of the evolutionary process of diverging: one set of researchers comment: ‘despite marked morphological differentiation, species divergence within Linaria is relatively recent and reproductive isolation has not yet fully evolved’ ( Ward et al., 2009, here). The species we see now diverged from their parent stock probably in the last few million years, which is recent by evolutionary standards.

Where does all this leave us with my rather insignificant weed? Well, I believe it may be a cross, or it may be a species for which I have not as yet found an illustration. Anyone with any suggestions is very welcome to leave me a comment.  But I am comforted by the confusion of others with this genus, for example that of Linnaeus in an important story about evolution which I’m going to tell in the next instalment. I’ll also be looking into the hidden agendas of some biology websites.

Following the genetic theme I’m looking for family-related music. First off, here’s the newish voice on the jazz scene, Gregory Porter, and his song Real good hands, with love to two of my readers. I recommend listening to any of his stuff you can find – he has one of the best male voices to appear on the scene in a long time, and he writes terrific songs.

Coming up very soon: a mutation discovered in Sweden and an aberration on the internet.