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

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 in ...

fronds. Fronds arise from creeping rhizomes and have long, delicate

rachis In biology, a rachis (from the grc, ῥάχις [], "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 c ...

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

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

. 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, : pronounced * hy, Կովկասյան լեռներ, : pronounced * az, Qafqaz dağları, pronounced * rus, Кавка́зские го́ры, Kavkázskiye góry, kɐfˈkasːkʲɪje ˈɡorɨ * tr, Kafkas Dağla ...

. 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 rich areas. In the

British Isles The British Isles are a group of islands in the 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 and Outer Hebrides, the Northern Isles, ...

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 Sidewalk, pavement. The term is mainly used in the UK and Ireland, where many of these landforms have devel ...

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 pavement. The term is mainly used in the UK and Ireland, where many of these landforms have developed dis ...

. 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