Flower colour and the seasonal quality of light?

Each year when the blues really kick in, I wonder whether there is a relationship with the seasonal quality of light.  Here are some blues from the garden 6th May; from top left moving clockwise, Germander Speedwell, Bluebell, Slender Speedwell, Green Alkanet, Thyme-leaved Speedwell, Field Forget-me-not, Ground-Ivy, Wood Forget-me-not, centre Grape Hyacinth.  All are wild or naturalised in the garden except the Grape Hyacinth which is in a pot:

This was followed closely by the pinks, 8th May; clockwise from top left Bush Vetch and Red Clover, three geraniums Dove's-foot Crane's-bill, Herb-Robert and Shining Crane's-bill, then Red Campion, Cuckooflower, Red Dead-nettle and centre Crab Apple blossom.  All common native species, in the garden or yard:

And then the whites and more yellows after the earlier Primroses and Cowslips, start coming, more or less simultaneously.  These collections were taken this week, 21st May.  There were also a fair few white umbellifers (Apiaceae) not included here.  Clockwise from top left Bramble, Common Mouse-ear, Bogbean, Hedge Mustard, Wild Rasp, Bog Stitchwort, Cleavers, Oxeye Daisy, centre Heath Bedstraw:

And the yellows;  clockwise from top left again, Yellow Rattle (I just love the tiny violet teeth), Yellow Archangel, Meadow Buttercup, Kingcup, Yellow Pimpernel, Bird's-foot Trefoil, Wood Avens, Hop Trefoil, centre Tormentil:

Is it just what I happen to be seeing around here, or has anyone else noticed a seasonal pattern of changing colours? Admittedly from now it becomes a riot of colours, but later in the summer the deeper pinks and purples become more prevalent.

An hour in Bridgnorth Cemetery, by John Handley

Though well recorded, Bridgnorth Cemetery is a short walk away from where I live and each year I enjoy a brief, but joyful display of a near threatened species in Great Britain.

Teesdalia nudicaulis in Bridgnorth Cemetery

Teesdalia nudicaulis, Shepherd’s Cress has been in decline for quite some time with many losses being recorded before the 1930’s.  T. nudicaulis favours open, free-draining, periodically disturbed shallow gravelly or acid soils.  In Shropshire it is typically associated with rabbit scraped heath grassland and upland screes as here on the edge of the Long Mynd:

The basal rosette of Teesdalia nudicaulis

Teesdalia nudicaulis showing the compressed spoon shaped fruits

The map below displays records of Teesdalia nudicaulis in Shropshire since 2000, showing records from Bridgnorth in the south east of the county, and Prees Heath in the north.  It’s most conspicuous presence is on the Long Mynd in the south, and Earl’s Hill just to the north.  Haughmond Hill near Shrewsbury and then Bulthy Hill to the west are the bulk of most of the remaining records with some scattered sites on the hills to the west.

The more recent losses in the lowlands are probably due to encroaching scrub. It is a winter-annual therophyte which means that it germinates and grows in the autumn, overwinters and then flowers and seeds when conditions are favourable in the spring, generally between March and June depending on the intensity of the spring sunshine.

In Bridgnorth Cemetery it grows where there is disturbance from rabbits which, I’m pleased to say, is currently a healthy population. It is reported to have a very short-lived seed bank which is a concern because without the disturbance from the rabbits, a closing sward won’t favour the germination in the autumn.  However there is some evidence from the Breckland Heaths that suggests that it might be more persistent than initially assumed and might have the potential to re-establish if there is further disturbance.

For more details see the BSBI Teesdalia nudicaulis, Shepherd's Cress species account