Very interesting, Hilary.
Here is a loose translation of the text on the notice board for the benefit of non-Greek speakers:
"The Church of the Assumption of the Virgin Mary was built in 1900 on this site, on which, according to historical references, was situated the ancient temple of Artemis Caryatis, and where an annual festival, The Caryateia, in honour of the goddess, took place. The Caryatids, priestesses at the temple, used to dance the "Dance of the Caryatids", originally a local dance but later danced all over Greece, up to our times. The ancient temple and the statue of the goddess Artemis were situated above a water source. Ruins of the temple can be seen in the stone structure of the newer temple (church?). In the church courtyard there are 4 plane trees, known as the Ancient Plane Trees of Menelaus. Their age can not be determined with accuracy but they are estimated to be approx. 2500 years old. According to the Roman historian Vitruvius, Menelaus had planted these circa 1100 BC".
Perhaps somebody can dig up the Vitruvius reference. (Marcus Vitruvius Pollio, 1st century BC).
As to karyon = nut in ancient Greek (Liddell and Scott Greek-English Lexicon), as opposed to karydi = walnut in modern Greek.
This was also the case for melon (milon)= fruit rather than specifically an apple. Hence the golden apples of the Hesperides, which Heracles had to steal as one of the 12 labours, were probably oranges.