Yellow

Two plants with bright yellow flowers, catch the eye in these parts at the moment.  One is native to the UK and the other is an invasive species.  First, the native one.  Common Toadflax (Linaria vulgaris) is a common sight around these parts at this time of year, but its familiarity does not detract from its beauty.

With flowers which resemble those of the Snapdragon, the two-tone yellow gives rise to the other common name of Butter-and-eggs.  Very popular with bees, they are strong enough to push their way in, past the 'bottom lip' which keeps the inner workings of the flower out of reach of lesser insects.

Nicholas Culpeper, in his 'Herbal' of 1653 has the Toadflax as a useful medicinal plant, used as a diuretic, laxative and aid for the treatment jaundice.  Rather more macabre, it was also mentioned as helping to 'drive forth' a dead baby from the unfortunate mother, as well as clearing the afterbirth.
The second of my yellow flowers is the non-native Canadian Goldenrod (Solidago canadensis).  Growing to about 5ft tall and topped with a long inflorescence of frothy, yellow flowers.

This too is very popular with many different pollinating insects, particularly the Hoverflies and Bees.  Not yet a problem in the UK, it has become a serious pest in China and its spread across the country is monitored very closely.  I remember it as a child, growing in our garden and making a beautiful sight, it's still doing so out in the 'wild'.