The "examples of former life on the Red Planet" were found by alien chasers in images of the Martian surface taken by the NASA Curiosity Rover, which is exploring the planet.
The images are beamed back to Earth and then placed on line by NASA for anyone to view.
The alleged tree stump was shown in a video by YouTube channel Paranormal Crucible.
In a promotional blurb for the video, the channel, which believes it has found other examples of life in similar pictures, said: "Intriguing object found by the Curiosity rover, this time a possible tree stump.
"This object definitely looks out of place and in my opinion could be the petrified remnants of a Martian tree.
"Object is around three feet in height, and with numerous discoveries of plant and animal life on Mars, it would be logical to assume, that a variety of tree either existed, or still exists on this enigmatic planet."
The video was highlighted by Scott C Waring, editor of ufosightingsdaily.com.
NASA*YouTubeAlien chasers claim this is a skull (left) and a tree stump (right) found on Mars.
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This still image strikes an uncanny resemblance to a figure of a woman
He said: "Paranormal Crucible makes a hypothesis that this could be an ancient tree stump on Mars.
"It's a good assumption since NASA said Mars was Earth-like when a solar explosion hit the planet, striping the atmosphere and oceans from its surface."
Mr Waring has been doing his own scouring through Curiosity images and claims to have found a possible alien skull.
He blogged: "Here is an alien skull I