You can hear a y at the start. There is not one.
composedTwo guesses in one spelling, one at the opening vowel and one at the sc.
heard aspyoubessent
spelledpubescent
saidpyoo-BESS-unt
pubescent begins with p and u.
English slips a y sound in front of a long u after most consonants, which is why pure, cute and music all carry one. The letter u takes the credit for both sounds on its own.
Four more
pubessent pubescant pewbessent pewbescent
The file is a short one. All 5 spellings of pubescent.