commonly known bradley cliff rare east central north_america named professor collected tennessee found growing small exposed sandstone cliffs species originated hybrid mountain originated sterile hybrid underwent doubling fertile phenomenon known studies indicate present population bradley arose independent sterile hybrids form sterile hybrids easily plants fertile habitats adapted thin acidic soil harsh environment native cliffs finds competitors isolated situation cliffs protects threats mining cliffs rock climbing activities cliff ecosystem destroy description small dark green form perennial notable characteristics dark stem color extends axis leaf blade deeply cut lobe base toothed edges characteristics variable observed individuals specimens rounded toothed edges lack dark coloration stem sterile fertile appearing size shape underground stems short parallel ground curving upwards spring cluster millimeter diameter covered narrowly triangular scales dark reddish brown strongly bearing like pattern scales millimeters long millimeters wide toothed edges stipe stem leaf blade upright centimeters long occasionally centimeters lacks wings brown shiny quarter times length blade small brown scales base stipe diminish hairs moves tip leaf overall shape blade ranges tapering ends width slightly wider short distance base tapering point apex squared base tip blade ranges centimeters long rarely centimeters centimeters width thin somewhat thick blade cut pairs possibly low high unusual specimens deeply subdivided lower upper variable shape tending squared broadly curved base typically widest near base lobe nearest located tends enlarged toothed vary millimeters length millimeters middle fertile pairs millimeters long dark brown color located margin covered edges white light tan color texture holds spores species number indicating origin june december variants reported specimens found growing shaded environment lacked color simply mistaken green conditions leaf texture ranges overlap described believed new species believed hybrid later shown simply form rounded sharp teeth form centimeter long discovered illinois form lacked dark color stipe base slightly larger specimens centimeter retained normal coloration structures fertile species closely resembles parent species characteristics exit distinguish toothed deeply cut fully cut dark color stipe extends upper lack stems overall shape leaf blade parallel sided lance shaped shows resemblance black ranges overlap identified distinctly triangular shaped leaf blade deeply cut leaves basal enlarged comparison parent species similar hybrid species parent graves hybrid dark color stipe ends base leaf blade distinct portion blade forms long tapering tip slight cut addition general reduction shows faint stipe likewise dark color stipe ends base leaf blade overall shape blade tends distinctly lance shaped somewhat deeply cut progressing lower half finally apex finally hybrid arose doubling essentially identical appearance close examination spores found abortive smaller fused grow fertile taxonomy scientific discovery occurred collected number specimens near bradley sent recognized species distinct named bradley publication identified hybrid intermediate english botanist proposed identical closely related conclusion based examination forms growing shade lacked color endorsed contemporary tennessee pointed collections dark stipe possessed lacked instead perceived specimens lower continued maintain theory affinity speculated hybrid intermediate speculated length hybrid origins scheme proposed later found recognize contribution ancestry suggested instead hybrid noting tentative suggestions lines studies following year showed product form sterile followed doubling restored fertility findings later supported analysis compounds showed combination compounds found showed pattern contains species specimen subsequently shown form showed descended contain compounds inherited walking verified simply form analysis 1980s supported hybrid origins species segregated change widely accepted current authorities recognize genus hybrids sterile hybrid resembles abortive spores smaller collected mountain georgia hybrid rarely collected studies multiple origins different populations originated doubling independently formed despite independent origins populations probably isolated addition parental species hybrid recognized named parental species collected specimens cliff near new_jersey thought collected described named honor specimens believed collected early date site collection submerged building preliminary report tennessee distribution found northern new_jersey pennsylvania southwest georgia alabama occasionally found missouri arkansas eastern oklahoma populations maryland new_york considered historical populations generally scattered frequent ecology conservation found steep acidic rocks altitudes meters sandstone common substrate found granite acidic rocks like soil formed rocks weather support slightly calcium tolerant usually grows tightly horizontal vertical exposed rock cliff faces small plants survive occur habitat soil typically composed mixture acidic sand rock organic materials including old frequently lost summer soil drier usually moist wet winter spring shade present dense shade tolerated growing hostile environment competes poorly plants slightly richer environments habitat protection strip mining threaten sandstone cliffs especially rock botanical collectors damaged populations toxic runoff atop cliffs affect threatened natural cliffs increased tree growth cliff base invasive cliff face slash cliff logging protected endangered species states illinois indiana new_jersey pennsylvania considered threatened ohio nature preserve ohio acquired contains state protected population
Asplenium bradleyi