Saguaro Sentinel (CR 9)

Huge Plant
Alignment: Usually neutral
Initiative: -1 (Dex); Senses: low-light vision, Listen +3, and Spot +8
Languages: Sylvan

AC: 22 (-2 size, -1 Dex, +15 natural), touch 7, flat-footed 22
Hit Dice: 12d8+84 (138 hp); DR: 10/piercing
Fort +15, Ref +3, Will +5
Speed: 20 ft.
Space: 15 ft./15 ft.
Base Attack +9; Grapple +28
Attack: Slam +18 melee
Full Attack: 2 slams +18 melee
Damage: Slam 3d6+11
Special Attacks/Actions: Thorns, trample 3d6+16
Abilities: Str 33, Dex 8, Con 25, Int 10, Wis 13, Cha 14
Special Qualities: plant traits, tough flesh
Feats: Alertness; Awesome Blow; Improved Bull Rush; Improved Natural Attack; Power Attack
Skills: Disguise +2*, Intimidate +12, Knowledge (nature) +10, Listen +3, Spot +8, and Survival +6 (+8 aboveground)
Advancement: 13-16 HD (Huge); 17-36 HD (Gargantuan)
Climate/Terrain: Warm deserts
Organization: Solitary or stand (2-5)
Treasure: Standard

Source: Sandstorm

This massive being possesses several thick, jointed arms raised to the sky. Long, needle-sharp thorns cover its thick hide, and tiny, deep-set eyes peer from between ridges along its body.

Saguaro sentinels are wastelands relatives of the treant. Like those tree folk, they consider themselves guardians of desert plant life. Unlike treants, though, they are not much concerned with good and evil. Saguaro sentinels stand over 30 feet tall, and some exceptional individuals approach 50 feet in height. They are thicker-bodied and retain more water than treants, having an average weight of 6,000 pounds. These cactus folk are normally slow to anger, but once aroused they are deadly juggernauts.

Saguaro sentinels speak Sylvan; those of above average intelligence also know the Treant language. Their voices are deep and booming.