A new study of photographs from the Mars rover Opportunity mission has been published in the scientific journal Advances in Microbiology. These images are alleged to show the sequential growth of objects that bear a marked resemblance to spherical fungi seen on Earth.

Some claimed at the time of their discovery that these were hematite (mineral) nodules. However this has been repeatedly disputed. It has been asserted that the object are, in reality, a poor match for hematite. Please find a link. below, to an article with further details.
https://interestingengineering.com/fungus-growing-on-mars