Since the Middle Ages, it's been known as May blossom. But should its name now be changed to April?
The flowering of the hawthorn bush has, for centuries, been an infallible sign in England that the month of May has arrived. But, this year, in our warm spring, its scented creamy-white flowers are appearing in many places a good three weeks earlier than normal.
It's not a one-off, according to the Woodland Trust, the green charity which is specialising in recording the signs that spring is getting earlier and earlier because of climate change.
So many things are happening, the trust says, that April is, in effect, becoming the new May. Swifts, which in the past returned from their winter migration and started to zip through British skies on about 10 May on average, are already here, the trust points out.
Those are only two of many signs of a massive change in the seasons that have been recorded in the past decade-and-a-half. In the past 30 years of steadily rising average temperatures, spring seems to have got about 10 days earlier in many ways - with the unfolding of the leaves of oak trees, for example, and the egg-laying of woodland birds.
But this year's early hawthorn is a particularly significant sign. "One of the most famous vernacular names for the hawthorn is the May-tree and culturally and historically it is seen as signifying the start of summer," said the trust's Dr Kate Lewthwaite.
"But thanks to the exceptionally mild start to the year we are experiencing, this summer signal is arriving three weeks earlier than the 11 May average."
Hawthorn has much mysticism surrounding it and, according to Celtic mythology, is the most likely plant to be inhabited by fairies. During May Day festivities, the flowers were used in garlands and branches were cut, set in the ground outside houses and decorated with wild flowers. Its purpose was to protect from evil spirits.
But the plant also has a doubly powerful Christian tradition. One part of it is the legend that the tree was the source of Jesus's crown of thorns. The other is the famous hawthorn in Glastonbury, Somerset, sprang from the staff of Joseph of Arimathea, the man who had Christ's body buried after the crucifixion.
The Glastonbury hawthorn, which has been written about for centuries, is certainly a special plant as it flowers twice a year - once in spring but also in midwinter, just after Christmas, regarded as miraculous in the Middle Ages. The original tree is no more but it has been widely propagated by graftings and cuttings.
Butterflies and bluebells: our changing seasons
* Bluebell Hyacinthoides non-scripta
Bluebells, usually thought of as a flower of early May to mid-May are now in full flower in southern Britain. The "Roman candle" blossoms on horse chestnuts are similarly out very early.
* Speckled wood butterfly Pararge aegeria
Several butterfly species have been seen in January and February this year.
* Squashed hedgehog Erinaceus europaeus
Hedgehogs have always hibernated or been dormant in the British winter, but unusually there have been squashed hedgehogs seen on British roads in February this year.
* Common frog tadpoles Rana temporaria
Frogspawn, usually laid in March, can now be seen in January - and on Christmas Day in Cornwall.