isoetid

is likely misspelled.

has no English definition.

As a noun isoetid

is a rosette plant that completes its entire life cycle submerged.

Elodeid is a hyponym of isoetid.

In botany terms the difference between isoetid and elodeid

is that isoetid is a rosette plant that completes its entire life cycle submerged while elodeid is a stem plant that completes its entire life cycle submerged, or with only its flowers above the waterline.

As nouns the difference between taxonomy and isoetid

is that taxonomy is the science or the technique used to make a classification while isoetid is (botany) a rosette plant that completes its entire life cycle submerged.