Resembling Geranium robertianum.
Rhizome: long-creeping, dark brown or black, forking.
Frond: 40 cm high by 15 cm wide, deciduous, monomorphic, blade/stipe ratio: 3:2 to 2:1.
Stipe: grooved, dull green, scaly at the base, soon falling, vascular bundles: 2, oblong.
Blade: 2-pinnate-pinnatifid, triangular, stiff, dull surface, very glandular, especially on the lower surface and the rachis.
Pinnae: 9 to 12 pair, lowest pair similar in form (not size) to the next pair; pinnules lower basal pinnule of the lowest pinnae cut like adjacent pinnules (unlike D. dryopteris); costae grooved above, continuous from rachis to costae; margins entire to slightly crenate; veins free, simple or forked.
Sori: round, closer to the margin, on both edges of the segments, indusium: absent, sporangia: brownish, maturity: midsummer.
Dimensionality: vertical stipe bends towards the horizontal in the rachis, but not as much as in the other species.
Habitat: calcareous woodlands or swamps, uncommon.
Hardy to -40°C, USDA Zone 2, requires a cool summer.
The similarity of the lowest pinnae pair to the second pair, the
glandularity (hand lens), consequent rank smell, and a generally more
robust plant distinguish it from the other species.
Polypodium robertianum Hoffm.
Aspidium calcareum Baumg.
Lastrea robertiana Newm.
Phegopteris calcarea Fée
Phegopteris robertiana (Hoffm.) Ascherson
Thelypteris robertiana Slosson