|Wood Forget-me-not Myosotis sylvatica, Rampton, 18th April 2020|
When you consider dry habitat Forget-me-nots there are only four common species to consider. The field guides indicate that the flower size may be the key identifying feature however the dimensions of the flower may not be adequate to distinguish one species from another. A quick check in the more serious literature emphasises this point, especially if you are (un)lucky enough to find a plant with flowers that are not the standard size e.g. sylvatica var. sylvatica.
Species considered here:-
Wood Forget-me-not Myosotis sylvatica Flower size 8-10mm dia.
Myosotis sylvatica var. sylvatica 4-8mm dia.
Field Forget-me-not Myosotis arvensis Flower size 1.5-3mm dia.
Changing Forget-me-not Myosotis discolor Flower size 1-3mm dia.
Early Forget-me-not Myosotis ramosissima Flower size 1-3mm dia.
To quote Sell and Murrell. m arvensis, ramosissima and sylvatica run into one another and are difficult to distinguish on precise characters but usually be recognised in the field when all taxa involved have become familiar. Well that's reasonably hopeful but then quotes Arther Chater who says "In Cardiganshire, pollen size is the only reliable difference between M. ramosissma and M. discolor."
Pollen size is well beyond me so, I just though I will put up a few photos from Cambridgeshire and see what we find.
This all started due to a potted up sample of Erophila developing three tiny Forget-me-nots which required identification. These three unexpected plants were small and the flowers were also small. I have never really looked at Forget-me-nots before so it seemed a good 'lock down' activity. Wood and Field Forget-me-not also grow in the garden.
Wood and Field FMN are both common so I will start with that pair.
M. sylvatica is really a garden plant and has large flowers typically 8-9mm across. It is planted and it escapes. Field FMN M. avensis is the poor relation with much smaller flowers. It is interesting to note that apart from the flower size, the other dimensions of the pedicle and stem are much the same for both species.
The pedicle is slightly longer that the length of the calyx. The calyx of the Wood FMN are open in fruit whereas the tips of the calyx are almost touching in Field FMN. This is apparently a good feature but just how reliable it is after the comments by Sell is to be seen. The angle of the pedicle from the stem is not reliable.
|Field FMN left, Wood FMN Right|
|M. avensis Field Forget-me-not showing spiral of forming flowers.|
|M. arvensis showing all pink petals.|
|M sylvatica Wood FMN showing stem hairs near flowers are flattened onto stem.|
|M. sylvatica, upper stem hairs|
|M. sylvatica Stem hairs|
|M arvensis, upper hairs|
|M. arvensis Stem|
Again the stem hairs in both species seem the same with lower stem hairs being long and patent and upper hairs being flattened. The leaves have long simple hairs on both sides plus on the midrib. No veins are visible. The leaves have no stalk. The leaves are alternate.
Calyx hooked hairs.
|M. arvensis calyx|
|M. sylvatica calyx|
As far as the two species growing in my garden are concerned, separation by flower size is easy. The problem comes with larger flowered versions of Field Forget-me-not, being occasionally recorded usually associated with woodlands. According to Alan Leslie, in the new Flora of Cambridgeshire, these large flowered versions are regarded as equated to subspecies .umbrata and have a different chromosome number 2n=66 ( 2n=36,48,52 is reputed for subspecies arvensis).
Field Forget-me-not growing in poor soil on the Fleam Dyke can have small flowers, down to a diameter of 1.5mm.
|Field FMN. Very small flowers from Fleam Dyke|
The situation with Wood Forget-me-not , M. sylvatica is also complicated by a variant M.sylvatica.var sylvatica which has flowers 4-8mm wide and is regarded as the original wild type. There is a another larger flowered variation var. cults with flowers 8-11mm which is usually a garden escape. These garden escapes can have bright blue flowers and also white flowers are not unknown.
I would conclude that any examples with intermediate size flowers would present quite a challenge since the open vs. closed calyx in fruit might not be 100% reliable?. This is where secondary features like the density of hooked calyx hairs come in.
Unfortunately the nutlet shape is not a reliable indicator of species as some M. sylvatica have nutlets with only a tiny rim, being much the same as M. arvensis. The other factor is that as the nutlets dry out, their shape changes.
|M. sylvatica left, M. sylvatica var. sylvatica middle, M. arvensis right.|
Early Forget-me-not Myosotis ramosissima.
|M. ramosissima Upper stem and flowers. No spiral, only two more buds hidden. (Isleham potted plant)|
|M. ramosissima. Flower less than 1.5mm diameter. Isleham site. Potted|
|M. ramosissima, Cambridge. Fruiting calyx are open.|
The plants from Isleham now potted up (with my Erophila) have paler flowers than the Cambridge site.
They both have fruiting calyces that are open so you can see the seeds developing. The three potted plants do not show the spiral of new buds. In the first photo two more new buds are hidden from view, becoming the tip of the stem. See below.
|M. ramosissima tip of flowering stem. (Isleham Potted)|
A limited sample from only one site and the Wild Flower Finder site
https://wildflowerfinder.org.uk/Flowers/F/Forgetmenot(Early)/Forgetmenot(Early).htm has photos showing that some plants have more buds than others. Even they have a limited number (estimate six), of buds in the spiral whereas the photo below has 14 buds in the spiral.
|Changing Forget-me-not showing extent of spiral with 14 buds.|
|M. ramosissima nutlets, no rim, convex both sides.|
|Top, Early FMN , below Field FMN M. arvensis.|
Changing Forget-me-not M. discolor
Two sub-species are present in the UK.
M. discolor ssp. discolor
Upper stem leaves nearly opposite.
Caylx is bell shaped with teeth not converging in fruit.
Yellow corolla at first 1.5 - 4mm across .
M. discolor ssp. dubia
Upper leaves alternate
Calyx is pear shaped with caylx teeth converging in fruit.
Cream/white corolla at first.
The following photos show ssp dubia.
|M. discolor, Cambridge showing white flower emerging.|
As the name suggests the flowers change colour as they open which is not uncommon in all these species but the difference is that they change colour after they have fully opened. They open being white or yellow and change to pale blue then darken. The internet shows examples that remain yellow or white so there is variation in unusual cases.
|M. discolor with open white flower. Stem hairs flattened to upper stem. Long patent hairs |
on lower stem and leaves.
|M. discolor Note yellow fornice ring stays yellow.|
|M. discolor nutlets , no rim, convex both sides|
Nutlets will not distinguish between Early and Changing Forget-me-nots, both have the same shape.
Conclusion. These four dry habitat Forget-me-nots are not quite as easy to separate as the field guides suggest and variation in flower size between Field and Wood requires careful attention to the calyx hooked hairs in order to conclude the identification in intermediate flowered plants.
In Cambridgeshire with a very limited sample it would appear that Early FMN (M. ramosissima) has flowers that point upwards when opening and Changing FMN (M. discolor) has flowers that open when pointing slightly downwards and then change colour and are fading by the time they are pointing vertically upwards. The spiral in Changing FMN seems to hold more flowering buds. Is this true in other parts of the country?
Rampton July 2020