Quickwood
Also called the spy tree, this plant appears to be an oak, although close examination reveals that it has a visage and sensory organs that resemble a distorted human face. It is 90% unlikely that the "face" is noticed unless the observer is within 10 feet of the Quickwood.
The Quickwood has excellent senses, with 120-foot infravision and the ability to detect vibrations through its roots, and aerial movements through its leaves. The Quickwood seldom moves, but it sends its roots up to 90 feet, through loose topsoil, to seize and hold immobile any creature weighing under 1,000 pounds. Roots cause no damage. They are too strong to be broken and take no damage from blunt weapons, and only 1 point of damage from piercing weapons. Edged weapons can sever roots, which are treated as large creatures with 10 hp each; damage inflicted to the roots does not count toward the tree's total. The quickwood will allow up to six of its roots to be severed before it withdraws the other 1d6+6 to safety. The roots pull prey to the Quickwood's mouth, which can clamp down to cause 3d4 points of damage to anything touching it.
The Quickwood can perspire and drench itself, so it is immune to fire; it is immune to lightning, poisons, and gasses. It is also immune to most other spells which do not affect plants specifically, including all mind-affecting spells. If attacked by a spell, the quickwood absorbs some or all of the spell's energy, and uses it to radiate fear in a radius of 10 feet per spell level absorbed. The spellcaster must make a saving throw vs. spells; if the save fails, all the spell's energy is siphoned into the fear effect. Otherwise, the spell has normal effects, and fear is simply a side effect.
The Quickwood can control up to 2d4 normal oaks within one mile, using them to gather information. Although it gathers no treasure, it may be charmed or otherwise convinced to guard treasure, which may be placed in the Quickwood's trunk. If acting as a guardian for some other being, a Quickwood can make a hollow drumming sound which can be heard for a mile or more.
