Learn Italian: Visito il giardino botanico, le cui piante sono rare. - I visit the botanical garden, whose plants are rare.

This is the trickiest part of using 'whose' in Italian! When you use cui to mean 'whose', the article before it must agree with the thing being possessed, not the owner. Here, the garden owns the plants (le piante). Since piante is feminine plural, we use le cui.

How literally does le cui piante translate to English?

Literally, it translates to 'the whose plants'. Whenever cui is used as a relative possessive pronoun (meaning 'whose'), it is almost always sandwiched right between the definite article (il, la, i, or le) and the noun being owned.

Why does the adjective rare end in -e here?

Adjectives must agree in gender and number with the noun they describe. Because rare describes le piante (a feminine plural noun), it takes the feminine plural ending -e. If it were describing masculine plural nouns, it would be rari.

Why is it giardino botanico instead of botanico giardino?

In Italian, descriptive adjectives like botanico almost always come directly after the noun they describe. This is a common pattern to remember since it is the opposite of English word order.