Herb Gathering

That is incorrect. Swiftthistle can be gathered by any Mageroyal or Briarthorn plant regardless of herbalism level. Of course assuming you have the proper skill to gather the herb in the first place.

Apprentice Herbalism = 1-75, not 75-149, making the ranks confusing; Rank of Herbalism does not equal rank of Lifeblood. Skill level determines rank of Lifeblood. Therefore: Lifeblood Rank 1 @ 75 - Requires level 1 Lifeblood Rank 2 @ 150 - Requires level 1 Lifeblood Rank 3 @ 225 - Requires level 10 Lifeblood Rank 4 @ 300 - Requires level 25 [url=http://www.wowhead.com/?spell=555

With gathering professions now comes new passive and cast abilities. Herbalism now gives you the ability "Lifeblood". With each rank up in Herbalism, you obtain a new rank in this skill.
Lifeblood is a very useful skill that you can cast. This is a self only heal, which is instant. Upon casting this, flowers will sprout around your character and you will be healed over time. The amount in which you are healed is increased with your skill/rank level.

Here are the different ranks for this ability in order of ranks and herbalism skill:
(mouse over the link to view the information for the rank)

75 - 149 (Apprentice):
Lifeblood (Rank 1)

150 - 224 (Journeyman):
Lifeblood (Rank 2)

225 - 299 (Expert):
Lifeblood (Rank 3)

300 - 374 (Artisan):
Lifeblood (Rank 4)

375 - 449 (Master):
Lifeblood (Rank 5)

450+ (Grand Master)
Lifeblood (Rank 6)

Happy Flower Picking! :)
(Edit: Corrected skill level vs rank, thanks!)