Heard spelling

perrianth

Spelled perianth. a doubled consonant

Does the r double in perianth?

No, and the temptation is real: the first syllable takes a short, hard stress, and English usually marks a short stressed vowel by doubling the consonant behind it.

Merry, berry and cherry all follow that rule. Perianth does not, because it was assembled out of Greek parts rather than grown in English, and peri keeps its single r wherever it goes.

Say

PERR-ee-anth

Letters

P-E-R-I-A-N-T-H