Learn Spanish (Latin America): ¡Cuántos pétalos blancos tiene esta margarita!

In exclamations, when cuánto is used with a noun to express quantity, it acts as an adjective and must match that noun's gender and number. Because pétalos (petals) is masculine and plural, you must use cuántos. If you were exclaiming about flowers (feminine plural), it would be ¡Cuántas flores!

Could I say ¡Qué muchos pétalos... ! instead to mean "How many petals"?

No, saying ¡qué muchos! is a common mistake for English speakers, but it sounds very unnatural in Spanish. When you want to exclaim about the quantity of a noun, always use a form of cuánto. Save ¡qué! for exclaiming about adjectives or adverbs, such as ¡Qué blancos! (How white!).

Why does the verb tiene come before the subject esta margarita?

In Spanish exclamations and questions that start with words like cuánto, cómo, or qué, the subject and verb are usually flipped. Instead of keeping the standard English order esta margarita tiene (this daisy has), it flows much more naturally in Spanish to invert them to tiene esta margarita.

Is the flower margarita related to the famous cocktail?