Enchanter's-nightshade and Rosebay Willowherb

To the casual observer these two native plants would not seem to be similar but they are, in fact, members of the same family: Onagraceae, Willowherbs. 

Enchanter's-nightshade, Circaea lutetiana

It grows in damp shady places in deciduous woodland and is perhaps easily overlooked. It is patch-forming with leafless spikes of small, delicate flowers. The ID features come largely in twos: leaves in opposite pairs, 2 petals, 2 sepals, 2 stamens and 2 seeds in bristly cases. The stigma is deeply lobed.

These scientific details perhaps don't do it justice. I quote Richard Mabey:

The tiny blossoms are mounted like butterflies on pins up the stems. They are formed

from two palest pink heart-shaped petals, mounted around two deeper stamens.

The English name Inchaunter's Nightshade occurs for the first time in Gerard. The Latin probably has links to Circe, the witch who transformed the crew of Ulysses into pigs. The plant has no links to witchcraft or medicine in this country.

Rosebay Willowherb,  Chamaenerion angustifolium

This common plant has a surprising history. Gerard first named it as a British species and until the mid eighteenth century it was a scarce northern plant on scree and rock ledges. By the mid nineteenth century it was spreading but still considered rare in Hertfordshire. The population exploded in World War One on land where wood had been felled to supply timber for the war effort. In World War Two there was a second expansion particularly on bomb sites in London. One popular name was generated: Bombweed. There is a theory that it spread more generally along, and then away from, railway tracks. Each plant produces about 80,000 seeds which can float freely in the slipstream of trains and on the breeze.

It is distinctive with tall spires of rose-purple flowers. Leaves are alternate, stalkless, strap-shaped and pointed. The large flowers have four petals, unequal in size, and four long, narrow, reddish sepals. The style is bent downwards and the stigma four lobed.

Acknowledgements: Harrap's Wild Flowers, Stace 4, Richard Mabey Flora Britannica and Grigson The Englishman's Flora.