Gorse is the 15th letter of the Gaelic tree alphabet, representing O. Its old Gaelic name was Onn, and in modern Gaelic it is conasg. It's a prickly shrub, which can almost always be found in flower somewhere, all twelve months of the year, and this means it has many positive connotations in folklore.
Snippets of lore
Conasg (Gaelic for gorse) means prickly or armed, appropriately enough as it's the spiniest plant around.
As gorse's branches, twigs and leaves are all spiny, which reduces water loss, it can survive extreme exposure to wind and salt.
Other regional names for gorse are whin or furze. In latin, it's Ulex europaeus.
Here's a lovely short Harry Rutherford poem about gorse. http://heracliteanfire.net/2009/01/26/poem/
Gorse bears yellow flowers all year round, and as they say, ‘When gorse is in bloom, kissing is in season.’
Gorse is a symbol of the sun god Lugh, as it carries a spark of sun all year.
Bees love gorse and it's a good source of food for them on warm winter days and in early spring.
In late spring, gorse flowers smell of coconut and vanilla.
Here's a poem from me, The Gorse is out behind Glencanisp. Audio too. http://www.pankmagazine.com/the-gorse-is-out-behind-glencanisp/
A decoction of gorse flowers counters jaundice.
Gorse seed pods explode in hot sun.
Gorse fixes nitrogen due to symbiosis with a bacterium in the roots.
Horses that eat gorse don’t catch colds (but presumably end up with perforated gums...)
The fierce fire of furze is ideal for baking.
Gorse boughs were used for creel-making. Ouch.
Gorse is a good windbreak and a gorse bush is the best place to dry washing – it naturally pins it in place.
A bundle of gorse is excellent for sweeping chimneys.
Here's a recipe for gorse flower wine. http://www.celtnet.org.uk/recipes/brewing/fetch-recipe.php?rid=gorse-flower-wine
Gorse flowers give yellow and green dyes.
Gorse bark gives a dark green dye. Add a bucket of urine and wait 3 hours.
Yellowed gorse, a poem by Fay Slimm http://www.poemhunter.com/poem/yellowed-gorse/
A missing home gorse poem, by Francis Duggan http://www.poemhunter.com/poem/i-d-love-to-see-the-gorse-in-bloom/
Gorse lifts the spirits of the downhearted, and restores faith.
Festival of the Golden Gorse is celebrated on 1 August (Lughnasa).
Gorse protects against witches.
Gorse’s magic is good for bringing a piece of work, a project, a relationship or a troublesome thing to a complete and final end.
Gorse symbolises joy.
Remember the nitrogen-fixing? Grow gorse for 7 years and the ground will be excellent for corn.
In 1778 a gorse crushing mill was set up in Perth. One acre of crushed gorse bushes will keep 6 horses in fodder for 4 months.
Bring gorse into the house in May to ‘bring in the summer’.
Giving someone gorse flowers is unlucky, for both giver and receiver. Best keep them for yourself!
Finally, Seamus Heaney says it all straight in Whinlands. Here with a bonus translation into Hungarian. https://www.babelmatrix.org/works/en/Heaney%2C_Seamus-1939/Whinlands/hu/18130-Rekettye
The next tree in the alphabet is heather.