Forget-me-not. How hard can it get?

Forget-me-not. How hard can it get?

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  1.5-6mm dia.
Changing Forget-me-not     Myosotis discolor                            Flower size  1-3mm dia.
Early Forget-me-not            Myosotis ramosissima                     Flower size  1.5-3mm 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 Arthur 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 pedicel and stem are much the same for both species.
The pedicel 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 pedicel from the stem is not reliable.

Field FMN left, Wood FMN Right

Apart from the size difference, the point of this photo is to show how the stem terminates in a fine display of 3-5 open flowers in both species.  The flowers emerge from a ammonite like spiral at the stem tip in Forget-me-nots.  The flowers start off pink and change to blue when open. The Yellow ring called the 'Fornice' at the base of the petals changes to white as the flower ages.

M. avensis Field Forget-me-not showing spiral of forming flowers.

Note the pink petals on the flower just about to open. The calyx holding the corolla tube is very hairy with hooked ends.  All the species considered here have these hairs. Also note the stem and pedicle have hairs that lie flat. They start patent ( at right angles) and turn through 90 degrees very quickly to lie against the stem.

M. arvensis showing all pink petals.

This plant has forgotten to change its petals to blue, uncommon but a well known variation.

M sylvatica Wood FMN showing stem hairs near flowers are flattened onto stem.

The above photo of Wood FMN showing the spiral of flowers which is much the same as in the previous photo of the Field FMN apart from the size of the flowers.

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  

Disregard the red colour in the photo of M. sylvatica above, the red is from the background now removed and since the hairs are transparent it shows the background colour.  The hairs from the base to just over halfway are curved to the point of being hooked. Outer hairs are straight. The hairs in M. arvensis do in general appear to be longer and more dense than in M. sylvatica. The tips of the calyx tend to be close together in M. arvensis and open in M. sylvatica , but this is not always clear cut and may be dependent on whether nutlets are present.

M. arvensis  

M. sylvatica Fewer shorter hooked hairs.

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 ( M. arvensis) 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.

The Wood FMN M. sylvatica flowers are about 8mm across , the var. sylvatica 5mm and the Field FMN M. arvensis about 3mm although they can be smaller.  These intermediate sized flowers would be easy to miss and identification depends on the calyx being open or closed and the density of the calyx hooked hairs. In this case the combination of calyx being open and the dense hooked hairs suggested M. sylvatica var.  sylvatica.  


Early Forget-me-not Myosotis ramosissima.

M. ramosissima Upper stem and flowers. No spiral, only two more buds hidden. (Isleham potted plant)

The standout feature of the three plants in the pot is that the flowers are tiny.  They were measured at just under 1.5mm across. The plants are also small being 50mm high with either one stem leaf or no stem leaves. The hairs within the inflorescence stem are appressed and lie pointing upwards.

M. ramosissima. Flower less than 1.5mm diameter. Isleham site. Potted

The flower has the same fused petals ( just at the base) , and the yellow fornice, just like the larger species but the petals are very pale with limited blue towards the outside and a white base.

M.ramosissima.  Cambridge

M. ramosissima, Cambridge. Fruiting calyx are open.

M. ramosissima.

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)

This lack of a multi-flowered spiral seems to be a feature of some Early FMN but other have a spiral similar to Changing FMN.  The above photo shows two flowers open and only two new buds forming. 

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.  It would seem that M. ramosissima can also have the spiral of buds.

Myosotis ramosissima ssp. ramosissima

Changing Forget-me-not showing extent of spiral with 14 buds.

The flowers of M. ramosissima often point upwards but M. discolor point downwards and horizontally and are often fading by the time they start to point upwards. 

M. ramosissima nutlets,  no rim, convex both sides.       

Top, Early FMN , below Field FMN M. arvensis.

Note the thin stem ( 1mm) and short pedicels on the Early FMN as well as the small flowers. A much thinner plant that given good growing conditions can grow quite tall. Generally seems to have fewer leaves than Field FMN. Tends to only display one or two open flowers that keep their yellow fornice.      

M. ramosissima. Fen Drayton. Note open calyx and short pedicles.

This plant has two stems, basal leaves only, no stem leaves and at this stage was only about 5cm high.

Changing Forget-me-not M. discolor  

Two sub-species are present in the UK , however whether they are easy to separate or they merge is yet to be investigated. They do have different chromosome numbers.
M. discolor ssp. discolor 2n=72
      Upper stem leaves nearly opposite. This applies only to the leaves at the base of the secondary      flowering stem only and some plants seem to lack this feature however it is worth looking for opposite leaves on other stems..
      Caylx is bell shaped with teeth not converging in fruit. Not sure about this bell shape.
      Yellow corolla at first 1.5 - 4mm across. Some are bright yellow but others are pale with just a touch of yellow. Flower colour does seem to be a distinctive feature of these two sub-species. 

M. discolor ssp. dubia 2n=24
      Upper leaves alternate at the point where a secondary flowering stem joins the main stem. In other words, the leaf at that junction is not matched with another leaf on the other side of the stem. 

Calyx is pear shaped with caylx teeth converging in fruit. Not sure about pear shape being much help.

Cream or white corolla at first without any yellow tinge.

M. discolor ssp. dubia.  Fen Drayton, Cambs. Single stemmed small plant.

 

M. discolor ssp. dubia. A very large plant growing in a shaded damp place and over 30cm high.

M. discolor ssp. dubia with the single leaf indicated, not having an opposite leaf.

       

The following photos show discolor ssp. dubia. Note how the leaves can come  up the stem on some plants unlike in M. ramosissima which has a longer inflorescence.

M. discolor, Cambridge showing white flower emerging.

The Changing Forget-me-not shares the same small size of the Early FMN with tiny flowers.

(  M. arvensis is often a large plant but sometimes can be tiny when growing in poor soil, so a plant an inch high with flowers of diameter 1.5mm can one tricky as it has the same structure with leaves well up the stem. It will show the longer pedicels which is a key feature to separate M. arvensis from M. ramosissima and M. discolor. An example is shown later.)

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 ssp  dubia with open white flower. Stem hairs flattened to upper stem. Long patent hairs
on lower stem and leaves.

M. discolor ssp. dubia

M. discolor ssp dubia 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.

As nutlets dry out they can show a rim on one side but I don't think this is a reliable feature.

M. discolor ssp. discolor

M. discolor ssp. discolor showing pale yellow corolla. 13 May 21, March

M. discolor ssp. discolor showing calyx tips apart however ssp. dubia tips are often not very different.

This example does seem to conform to the literature but others are not so clear cut.

M. discolor ssp. discolor opposite leaves at upper stem junction.

M. discolor ssp. discolor upper stem junction not showing opposite leaves.

Not all plants of subspecies discolor at Whitemoor Prison, March,  showed the expected opposite leaves so this puts into doubt how reliable this distinction in the literature is. There is also the complication of a leaf within the inflorescence being regarded as a bract not a leaf so the exact rules will need more investigation.

 The 'discolor group' of Myosotis is very different from all the other species found in Europe in that it has a much larger pollen size *and several species/sub-species exist including M. balbisiana and M. persoonii ( 2n=48  twice ssp. dubia). M. discolor ssp. discolor is thought to be a hybrid and that might explain why its features are variable.

*ref http://phylodiversity.net/rwinkworth/publications/files/3.pdf

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 start blue and stay blue until they fade and Changing FMN (M. discolor) has flowers that open when pointing slightly downwards and then change colour from either white or yellow to become blue, then are fading by the time they are pointing vertically upwards.  Structure can be a difference between M. discolor and R. ramosissima, where M. discolor has a short length of inflorescence compared with a long leafed stem whereas M. ramosissima has a long inflorescence compared to a shorter stem with few leaves. More to learn about this tricky group as some plants do seem to break the expected rules stated in the literature.

Peter Leonard
Rampton July 2020

end.
Updated May 13th 2021 with additional photos and improved comments on difference between the two versions of M. discolor and the structure differences between the species.

Plant Structures.

1) M. arvensis

M. arvensis. 7cm high plant with single stem showing upward pointing flowers, long pedicel and  lengths of leafy stem and inflorescence. This is not a typical plant but chosen as its very small flowers could mislead into thinking this was a M. ramosissima.

2) M discolor ssp. discolor.

M. discolor ssp. discolor showing primary stems have opposite leaves where they join.

Second example without opposite leaves at main junction.

M. discolor ssp. discolor.

The second example with four stems shows that where the two main stems join, only a single leaf is present. Stem 2 has a junction with four flower showing which might be regarded as the start of another inflorescence and opposite leaves so although the main site for opposite leaves does not hold true it may be that looking around the stems will show other sites for opposite leaves, see below.  A similar situation occurs in the lower stem on the right where a junction displays opposite leaves.  A final point about these structure photos of discolor ssp. discolor is the few stem leaves. Also note the very short pedicles, a feature shared with M. ramosissima. 

Close up.

Enlarged from the plant shown above, a junction that displays opposite leaves with four flowers without an obvious stem. 

3) M. discolor ssp. dubia.

Sub-species dubia showing no opposite leaves. 

The inflorescence will get longer as the flowers develop and the spiral straightens. The number of stem leaves varies from just one to four on this plant and they do not go far up unlike some dubia plants.  

M. discolor ssp. dubia  All alternate leaves. King's Dyke.

Different population and different structure with alternate leaves held close to vertical stem before flowering shoots spilt off high up.  

Summary.  To separate M. discolor into sub-species discolor and dubia, first check first the colour of the newest flower to open, before it changes colour. If white or pale cream you have a dubia, if slight yellow is present or if you are lucky bright yellow then you have a discolor.     Next look for any opposite leaves which may occur at the junction of the second stem or even at other stem junctions.  This has not been seen in dubia but one plant from the Booker site in Cambridge had almost opposite leaves at a junction so the chances are, this feature is subject to interpretation. 

M. discolor ssp. dubia, Booker site, Cambridge

How much displacement does a opposite leaf have to have before it becomes alternate?  I regard this as not opposite but it takes a close look.

 The calyx tips are slightly more separated in discolor but I think this is too marginal a feature to be useful, unless you really have a good eye for it and a lot of magnification.

Dubia may have slightly more stem leaves but again this is tricky.