The mild weather last month saw me sally forth coatless on my early morning walks, ignoring the old adage to “ne’er cast a clout ‘til May be out”.

But does May refer here to the month or to the hawthorn blossom, which is also called May or Mayflower? There seems to be some dispute about this.

The Woodland Trust claims that the saying refers to the hawthorn, which flowers in May and early June, although first blossom is frequently recorded in April. There is an advantage to this assumption because the time of flowering of wild plants is affected by temperature and therefore provides a more reliable guide than a fixed date such as the first of June, when temperature may vary considerably. For example, since 1910, average May temperatures across England have ranged from 8.5°C in 1941 to 13°C in 1992 and 2008.

Indeed, it is thought that, due to climate change, spring in the UK is advancing, with plants such as the hawthorn flowering earlier. A 2002 study of 385 British plants found that the dates that they first flowered were, on average, 4½ days earlier than they had been in the previous 40 years.

On the other hand, the Oxford Dictionary of English Proverbs gives the first known record of this saying as the 1627 Spanish version, ‘Hasta Mayo no te quites el sayo’, meaning ‘Don’t leave off your coat until May’, referring to the month rather than the flower. But it is not unlikely that the saying originated in England before crossing the channel, so it is just possible that a translation error switched the meaning from the flower to the month.

Certainly hawthorn is a conveniently ubiquitous guide to your wardrobe choices. It is native to the UK and very common everywhere apart from northern Scotland. It is one of the most widespread hedgerow species, its dense thorn-bearing branches producing a very effective stock-proof hedge, but it will grow into a small tree with a height of around 30 feet when left uncut. It can be long-lived, and the Hethel Old Thorn in Hethel churchyard is reputed to be over 700 years old.