Learn Farsi: دارچین منبع غنی آنتی‌اکسیدان به شمار می‌رود. - Cinnamon is considered a rich source of antioxidants.

It is the present tense of به شمار رفتن (be shomâr raftan). Literally meaning "to go to count," it is a formal way to say "to be considered" or "to be counted as." Notice that it directly follows the classification (منبع غنی آنتی‌اکسیدان) without needing an extra preposition like "as" before it.

Can I use محسوب می‌شود instead of به شمار می‌رود in this sentence?

Yes, absolutely. محسوب شدن (mahsub shodan) is taught alongside به شمار رفتن because they are essentially interchangeable formal verbs for "to be considered." Using محسوب می‌شود here would sound just as natural and academic.

Why isn't there a word for "a" (like یک) before منبع غنی (rich source)?

In formal Farsi, general definitions and classifications often omit the indefinite article یک (yek) or the indefinite suffix -ی (-i). Leaving the noun phrase bare (دارچین منبع غنی...) sounds more definitive and encyclopedic than treating it as a single, countable instance.

How do I pronounce the invisible Ezafe links in منبع غنی آنتی‌اکسیدان?

The phrase is pronounced manba'-e ghani-ye ânti-oksidân. The first Ezafe connects the noun منبع to its adjective غنی with a simple -e sound. The second Ezafe connects to the next noun آنتی‌اکسیدان. Because غنی ends in a vowel, the second Ezafe becomes a sound to bridge the gap smoothly.