Uprooting plants and other growths from their source:
A. The general rule:
One who uproots any plant growth from its source is liable for the prohibition of “uprooting an item from its source of growth”. One who uproots with an irregularity, such as using his teeth, is Biblically exempt, although doing so is Rabbinically forbidden.
B. Case examples:
Removing moss and plant growth from vessels and objects: Moss and other plant growth which have grown on vessels or objects as a result of moisture are forbidden to be removed on Shabbos.
Moving a stone that has moss growth: It is forbidden to lift a stone that contains moss growth in a way that it is lifted from the ground, as by doing so one temporarily limits its nurture from the ground which is similar to uprooting.
 This refers to the thread like growths that come out of some thorns and thistles. [Rashi Shabbos 107b] The English equivalent to this is the Humulos Lupulos plant although it does not seem to fit this description.
 As although they are not attached to the ground, nevertheless by doing so one uproots the growth from its source which is the thorn. [ibid]
 These growths are considered similar to plants connected to the ground as this is the way these plants grow. Hence one who removes them from their area of growth is liable for uprooting an item from its source of growth. [ibid]
 This is despite that regarding the laws of impurity it is considered like it is detached, nevertheless regarding Shabbos they are Biblically considered attached. [ibid]
 Implied from 312/6 which only allows doing so for Kavod Habriyos.