Pliny,

Historia Nātūrālis 22.57

Hēliotropiī mīrāculum saepius diximus cum sōle sēsē circumagentis etiam nūbilō diē; tantus sīderis amor est. noctū velut dēsīderiō contrahit caeruleum flōrem.

I have often spoken of the miracle of the sunflower, which turns itself round with the sun even on a cloudy day, such is its love for that star. At night it closes up its blue flower as if it were longing for the sun.

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