I don't understand how the sounds of the Latin root are similar/related to those of the IndoEuropean root. Nor do I get the meaning of the Indo-European root bhel that would cause it to find its way into such *apparently* disparate words as flower, bleed, bless, foliage, blossom and blade.

Basically, different IE daughter languages changed vowels, consonants, and stress accent in different ways. Flower and foliage come basically from Latin, but blood, bleed, blossom, etc., come from Old English. In the Italic languages (Latin and its sisters like Umbrian and Oscan), PIE *bh usually becomes an f, but in Germanic languages *bh, in initial position, becomes b. As for the fl vs fol, resonants (i.e., r and l) in PIE roots (like *bhel-) sometimes come before the vowel of the root and sometimes after it (e.g., CVRC ~ CRVC, where C is a consonant, R is a resonant, and V is a vowel), depending on things like stress, and possible affixes (prefixes or suffixes). English has borrowed so many words from different branches of IE that it is sometimes difficult to imagine the various words all being related, but they are as best as we can tell. PIE is a reconstructed language and not an attested one. Take the PIE root *gwem- 'to go': in Greek bainō, Latin venio, Sanskrit gam (root), gacchāmi (from *gwem-sko-mi), Old English cuman, English come.

You might want to take a look at a textbook on historical linguistics. W P Lehman has written an affordable one.

Ceci n'est pas un seing.