Cheilanthes feei, a xerophytic fern, is commonly found occupying limestone bluffs in Southeast Missouri. Its known range encompasses southwestern Canada, extends south to north central Mexico, and east to the Ohio and Mississippi River valleys of the Midwestern United States. Although C. feei has a broad distribution, it inhabits a very narrow niche, one-half to one meter from the bluff tops, often in full sun. Data from previous research indicate that C. feei protonemata exhibit a decrease in maturation and viability as moisture levels of the supporting growth media increase. We hypothesized that water levels and osmolalities present in the limestone in C. feei habitat are approximately those required by growing protonemata in order for their development to continue to maturity. Rock samples were taken from three sites in southeastern Missouri, one set from a protected biological station, another set from a privately owned site along a paved suburban road, and another from a publicly accessible ridge overhanging a boating access to a riverway. Rock samples were tested using standard hydrogeological formulas for specific retention and porosity. In addition, the osmolalities of rock sample infusions were measured. Our data indicated that, while there was no significant difference in porosity, specific retention, or osmolalities in or of the sample rocks taken from sites containing C. feei and those nearby sites where the fern was not present, the moisture levels within the limestone at each site fell within the range of moisture required by protonemata to thrive. These data also suggest that the water quality may provide some cryoprotection. This evidence supports our hypothesis that the habitat restrictions of C .feei may be partially due to the water requirements of the protonemata, however it also suggests that water quality may play a role in C. feei survival.

Key words: Cheilanthes feei, gametophyte, porosity, protonemata, southeast Missouri, specific retention