"Phytocretions" are calcite plant encrustations that form in standing water above the sediment surface (similar to tufa or "spring chalk") but mimic rhizoliths in their outward morphology.

It is important to recognize this type of carbonate in the fossil record. If confused with rhizoliths, they may be interpreted as soil carbonates. Instead, they form above the sediment surface in standing water during a very short period of time (the growing season of the saltgrass plant). Rather than recording dry conditions (as pedogenic carbonates often do), they record ambient aquatic conditions at the time of their precipitation.

These particular samples (left) were found forming around saltgrass plants on a playa in Nevada. Scale bar is 0.5 cm for photos A-C.

 

For more information on phytocretions, see Liutkus 2009.