Comments from JPL:
Needless to say, no, this is not evidence of fungi on Mars. The images that are being posted are from the Opportunity rover, which discovered mineral spherules that were nicknamed 'blueberries' based on their size and shape. Scientists didn't rely solely on visual information to identify them; they used instruments on the rover to measure chemical and mineral information within these spheurles (sic), confirming they were in fact minerals that formed in the presence of water.
The blueberries are one of the best-known discoveries of the Opportunity mission, something countless Mars scientists from around the world would be familiar with and have studied the data for.
Furthermore, the authors ignore other data that easily disprove their claims; for example, many features claimed to be biological are known to typical martian rocks, sand, dust, and ice that change in appearance due to weather, lighting, or rover interactions. Other features superficially resemble fungi but actually are commonly observed, abiotic features in rocks that occur from geochemical changes or by erosion from wind.
Color enhanced images from Mars.