Suffering with Scurvy

Don't panic, it's not quite as horrific as it sounds. The suffering revolves around the plant in the picture below. It's Common Scurvygrass, (disclaimer: I've since realised it could also be Danish Scurvygrass, it's difficult to say either way with these small specimens) found whilst exploring a nice bit of saltmarsh. I took a few pics but no sample, headed home afterwards and realised I can only safely record it as 'Common Scurvygrass agg' (and not even that now...) But why am I stuck at 'agg'?  What are the options? And why am I not happy to leave it at 'aggregate' level?

Common Scurvygrass 'agg'

Without properly grilling it, the plant in the pic could be any of the following taxa:

Cochlearia officinalis ssp. officinalis - a highly variable plant, nationally very common in saltmarshes

Cochlearia officinalis ssp. scotica - old (pre-2000) records from various parts of the Skye coastline

Cochlearia officinalis ssp. atlantica - might not even warrant subspecific status, possibly just a variant

Cochlearia officinalis x Cochlearia danica - may occur where the parents meet - insert facepalm emoji

The good news is that, according to Stace 4 at least, the hybrid isn't supposed to occur in northern Scotland. Of course, the plants won't have read Stace 4 so they may not be playing by his rules. Happily, in this instance Stace's view is entirely backed up by the BSBI map, as can be seen below

Known distribution of the Danish x Common Scurvygrass hybrid in Scotland

So it seems pretty unlikely that my plants (and there were hundreds of them) are the hybrid. Phew. The picture gets quite confusing when you look at the maps for Common Scurvygrass ssp scotica and ssp officinalis. I've jigged the maps so they only show records from the year 2000 onwards. The black dot is situated over the saltmarsh in question.

This is the 2000-2022 map for Common Scurvygrass 'aggregate'

This is the 2000-2022 map for Common Scurvygrass s.s.

This is the 2000-2022 map for Common Scurvygrass ssp. officinalis

And this is the 2000-2022 map for Common Scurvygrass ssp. scotica

For completeness, here's the map for Danish Scurvygrass. Note the linear distribution in the far east - this is where it's colonised and spread along the verges of salted inland roads. I've no clear idea why the hybrid between Danish and Common Scurvygrass doesn't occur on Skye seeing as both parent plants are here, though in truth I guess the same can be said for most of Scotland. Perhaps it's a latitude thing.

2000-2022 map for Danish Scurvygrass Cochlearia danica

Hopefully you will have already noticed that by far the most frequently recorded taxon on Skye is Common Scurvygrass 'agg'. Once I'd crunched down to subspecies level I noticed something interesting; both officinalis and scotica have been recorded from nearby Rum and from the Outer Hebs post-2000, but officinalis has never been recorded from Skye and scotica hasn't been recorded here since 1993. The obvious implication being that Skye's populations of Common Scurvygrass haven't been critically looked at for a number of years (blame the frantic Atlas 2020 square-bashing for that...) However, were they to be critically checked nowadays they should, in theory, belong to the scotica subspecies. That makes sense, right?

I queried this with Stephen Bungard, BSBI Recorder for Skye and the Small Isles (which coincidentally includes Rum, an island he has extensively botanised in the past) who responded with "they certainly aren't all scotica". Aah right, well I'm not about to disagree with him. So what's going on?

The taxonomic boundaries for some of the Cochlearia scurvygrasses are, how can I best put this, let's just say that they are a long way from being universally accepted by all. Different views have been bantered back and forth over the years as to how best to deal with what has become known as the "Cochlearia officinalis Group", which is precisely the group I'm struggling to get to grips with right now.

Generally speaking, the BSBI Handbooks can be considered to be amongst the very best identification works available for the plant families they cover. Scurvygrasses are part of the crucifer (cabbage) family and I happen to own a copy of the Crucifers of Great Britain and Ireland, published in 1991. The author, Tim Rich, is an incredible plant scientist and a highly-skilled field botanist and he split the Cochlearia officinalis Group as follows (asterisk denotes the taxa present in the Inner Hebrides): 

Cochlearia officinalis s.s. - Common Scurvygrass*

Cochlearia atlantica - Atlantic Scurvygrass

Cochlearia pyrenaica pyrenaica - Pyrenean Scurvygrass*

Cochlearia pyrenaica alpina - Alpine Scurvygrass

Cochlearia scotica - Scottish Scurvygrass*

Cochlearia micacea - Mountain Scurvygrass

Clearly Tim didn't just invent these names on the spot, he rigorously followed up type specimens in herbaria, visited type localities and made his own comparisons, measurements, drawings and field observations. He also went on to cultivate many of the species he studied. Hence his interpretation of the C.officinalis Group very definitely holds water. Or it did in 1991. Nowadays DNA analysis has resulted in a huge number of taxonomical upheavals, not least in plants. 

The current botanical bible, published in 2019, is Stace 4. It's generally as bang up to date with the latest taxonomical revisions as any Flora out there. Molecular work is still ongoing for many species, but the families at least should be largely sorted. Not surprisingly, Stace treats the C.officinalis Group a little differently to the BSBI Handbook. He breaks it down as follows:

Cochlearia officinalis officinalis - Common Scurvygrass*

Cochlearia officinalis scotica - Common Scurvygrass*

Cochlearia pyrenaica pyrenaica - Pyrenean Scurvygrass*

Cochlearia pyrenaica alpina - Pyrenean Scurvygrass

Cochlearia micacea - Mountain Scurvygrass

The main differences are that Cochlearia atlantica has been subsumed into Cochlearia scotica which itself has been subsumed into Cochlearia officinalis. Basically, Stace has lumped them into one species, which presumably follows the latest taxonomical findings. 

I'll very quickly run this plant through the Cochlearia key in Stace 4, dealing with the relevent half of each couplet only and ignoring anything to do with the fruits (because they haven't formed yet)

1) Flowers in racemes, not solitary, all or mostly without bracts >>2

2) Stems less than 50cm tall >>3

3) Basal leaves cordate to very broadly cuneate at base >>4

4) Upper stem leaves sessile not petiolate, often clasping stem >>5 (this is where C.danica could drop out - I can't see the base of the upper stem leaves in these pics)

5) Biennial to perennial, rarely woody at base >>6

6) Upper stem leaves distinctly clasping, flowers (5)8-15mm, maritime and lowland >> C.officinalis (agg.)

What I need to do next is return to these plants and take accurate measurements of the leaves and petals (and the fruits when they form), take lots more photos and note the precise shape of the leaf bases. I also need to dry some fruits to see whether or not they have reticulate veins before finally coming to a determination as to the subspecies involved. That's the plan, anyway.

And why bother with all that when I could just leave it as 'agg'? Well firstly, because how else will I learn these things if I don't put myself through the entire identification process. Secondly, Stephen says they aren't all scotica, yet that's the only subspecies so far known from Skye - I want to know what's going on there. Could they be the mysterious atlantica, or is officinalis here too? Seems odd that it wouldn't be if it really is on Rum and the Outer Hebs. And lastly, because it could be, oh I dunno...fun?

It's been shown that if you bring mountaintop Cochlearia pyrenaica down to low levels and cultivate it through several generations, it will end up pretty much the same as Cochlearia officinalis, strongly suggesting they are in fact one in the same species. For this reason, Stephen records all coastal scurvygrasses around Skye as Cochlearia officinalis agg (apart from when it's C.danica obviously). And seeing as he is by far and away the most prolific plant recorder in the area, that's the reason why the bulk of Skye's more recent Common Scurvygrass records are of the agg.

Blimey, that was a lot of effort to say that I couldn't ID a plant! Bet you can't wait until I start on the whitlowgrasses. 

Right, music time. There's no decent reason for tonight's choice of toonage other than I do enjoy listening to a bit of early Korn. This is Somebody Someone from way back in 1999. If anybody's interested, Korn have just released a new album and are still touring. They'll be playing Download on 10th June, I think it's their only UK date this year. Time to get that stomp on, hope you enjoy!