''Gymnocarpium robertianum'', the limestone fern or scented oakfern, is a fern of the family

Cystopteridaceae Cystopteridaceae is a family of ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family is placed in the suborder Aspleniineae of the order Polypodiales, and includes three genera. Alt ...

Description

''Gymnocarpium robertianum'' has small (10–50 cm), deltate, two- to three-

pinnate Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, and ...

fronds. Fronds arise from creeping

rhizomes In botany and dendrology, a rhizome ( ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

and have long, delicate

rachis In biology, a rachis (from the [], "backbone, spine") is a main axis or "shaft". In zoology and microbiology In vertebrates, ''rachis'' can refer to the series of articulated vertebrae, which encase the spinal cord. In this case the ''rachi ...

. The sori are borne in round clumps on the underside of the blade and lack an

indusium A sorus (: sori) is a cluster of sporangia (structures producing and containing spores) in ferns and fungi. A coenosorus (: coenosori) is a compound sorus composed of multiple, fused sori. Etymology This Neo-Latin word is from Ancient Greek � ...

. This species differs from the closely related ''G. dryopteris'' in having a densely glandular

as well as a more sparsely glandular underside to the blade. ''Gymnocarpium robertianum'' is thought to hybridise with ''G. appalachianum'' giving rise to ''Gymnocarpium'' × ''heterosporum'' W. H. Wagner. This hybrid was only known from Pennsylvania where it has now been eradicated. The hybrid between ''G. robertianum'' and ''G. dryopteris'' is called ''Gymnocarpium'' × ''achriosporum'' Sarvela. This taxon is known from Sweden and Quebec.''Gymnocarpium robertianum''
at Flora of North America

Distribution and habitat

''Gymnocarpium robertianum'' is a circumboreal species with populations in Europe, North America and the

Caucasus Mountains The Caucasus Mountains * * Azerbaijani: , * * * * * * * * * * * is a mountain range at the intersection of Asia and Europe. Stretching between the Black Sea and the Caspian Sea, they are surrounded by the Caucasus region ...

. This species is protected in Illinois and Michigan and is protected under the Flora Protection Order in Ireland. This species is a

calcicole A calcicole, calciphyte or calciphile is a plant that thrives in lime rich soil. The word is derived from the Latin 'to dwell on chalk'. Under acidic conditions, aluminium becomes more soluble and phosphate less. As a consequence, calcicoles grown ...

and as such is restricted to

alkaline In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...

rich areas. In the

British Isles The British Isles are an archipelago in the Atlantic Ocean, North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner Hebrides, Inner and Outer Hebr ...

its preferential habitat is

gryke A limestone pavement is a natural karst landform consisting of a flat, incised surface of exposed limestone that resembles an artificial pavement. The term is mainly used in the UK and Ireland, where many of these landforms have developed dist ...

s in

limestone pavement A limestone pavement is a natural karst landform consisting of a flat, incised surface of exposed limestone that resembles an artificial Sidewalk, pavement. The term is mainly used in the UK and Ireland, where many of these landforms have devel ...

. In Michigan the species is most frequent in

Thuja occidentalis ''Thuja occidentalis'', also known as northern white-cedar, eastern white-cedar, or arborvitae, is an evergreen coniferous tree, in the cypress family Cupressaceae, which is native to eastern Canada and much of the north-central and northeastern ...

swamps.
Abstract on ''Gymnocarpium robertianum'' in Michigan

References

External links

*''Gymnocarpium robertianum'' at Flora of North Americ

*Distribution of ''Gymnocarpium robertianum'' in the British Isles at BSBI map

*''Gymnocarpium robertianum'' at Hardy Fern Librar

Gymnocarpium, robertianum Ferns of the United States Taxa named by Edward Newman Flora of Canada {{Polypodiales-stub