''Homalosorus'' is a genus of fern with only one species, ''Homalosorus pycnocarpos''. It may also be referred to by its older synonyms ''Athyrium pycnocarpon'' and ''Diplazium pycnocarpon''. Commonly referred to as the narrow-leaved glade fern, narrow-leaved-spleenwort, or glade fern, it is endemic to eastern North America and typically grows in moist woodlands. Once classified in the family

Athyriaceae The Athyriaceae (ladyferns and allies) are a family of terrestrial ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family is placed in the suborder Aspleniineae, and includes two gene ...

due to its linear, often doubled sori, in the

Pteridophyte Phylogeny Group The Pteridophyte Phylogeny Group, or PPG, is an informal international group of systematic botanists who collaborate to establish a consensus on the classification of pteridophytes (lycophytes and ferns) that reflects knowledge about plant relation ...

classification of 2016 (PPG I), it is placed in the small family

Diplaziopsidaceae Diplaziopsidaceae 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, and includes two genera. Alternatively, it may be treat ...

, whose other three species are native to east Asia. Other sources place the genus in the subfamily Diplaziopsidoideae of a very broadly defined family Aspleniaceae, equivalent to the suborder Aspleniineae in PPG I.

Description

''Homalosorus pycnocarpos'' grows from creeping stems. Its clustered fronds grow to about long and wide. The leaf blade is oblong-lanceolate and once-pinnate. The pinnae are linear and either more-or-less entire or with shallow indentations. The fertile leaves are similar to the sterile leaves, but narrower, with more widely spaced pinnae. The sori are long, straight or slightly curved, borne in two lines along the underside of a leaf pinna. The indusia are thick and prominent. The arrangement of the sori gives rise to its

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

''pycnocarpos'' ('crowded fruits').

Taxonomy

The genus ''Homalosorus'' was erected by Rudolfo Pichi-Sermolli in 1977. ''Homalosorus pycnocarpos'' in its present circumscription was first described by André Michaux in 1803 as ''Asplenium angustifolium''. However, this name was illegitimate, since it had already been used by

Nikolaus Joseph von Jacquin Nikolaus Joseph Freiherr von Jacquin (16 February 172726 October 1817) was a scientist who studied medicine, chemistry and botany. Biography Born in Leiden in the Netherlands, he studied medicine at Leiden University, then moved first to P ...

in 1786 for a different species of fern. (The description "narrow-leaved" in the English name is a reflection of the original specific epithet: .) In 1804, Kurt Sprengler published a description of a species he named ''Asplenium pycnocarpon''. He wrote that he doubted that it was the same as Michaux's ''Asplenium angustifolium'', since that species was described as having smooth-edged leaves. However, later authors have regarded the two as

synonymous A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

, so that ''Asplenium pycnocarpon'' is the first legitimate name, and hence the

basionym In the scientific name of organisms, basionym or basyonym means the original name on which a new name is based; the author citation of the new name should include the authors of the basionym in parentheses. The term "basionym" is used in both botan ...

of ''Homalosorus pycnocarpos''.

Classification and phylogeny

The species has been placed in several genera. It was first described in '' Asplenium'' and later transferred to '' Athyrium''. In 1977, Pichi-Sermolli transferred it to the monotypic genus ''Homalosorus''. The ''Flora of North America'' placed it in ''

Diplazium ''Diplazium'' is a genus of ferns that specifically includes the approximately 400 known species of twinsorus ferns. The Greek root is ''diplazein'' meaning ''double'': the indusia in this genus lie on both sides of the vein. These ferns were ...

'' as ''Diplazium pycnocarpon'', noting its similarity to the east Asian species then known as ''Diplazium flavoviride''. It was later shown that ''Diplazium flavoviride'' and ''Homalosorus pycnocarpos'' (as ''Diplazium pycnocarpon'') were closely related to the genus '' Diplaziopsis''.

Molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

studies in 2011, 2012 and 2017 showed that ''Homalosorus'' and ''Diplaziopsis'' form a clade, with ''Homalosorus pycnocarpos'' sister to the species of ''Diplaziopsis''. In 2011,

Maarten J. M. Christenhusz Dr Maarten Joost Maria Christenhusz (born 27 April 1976) is a Dutch botanist, natural historian and photographer. Career He was born in Enschede, the Netherlands, received his undergraduate and master's degrees from Utrecht University in ...

and Xuan-Chun Zhang created the family

, containing both ''Diplaziopsis'' and ''Homalosorus''. Diplaziopsidaceae is accepted in the

classification of 2016 (PPG I). Other sources place the genus ''Homalosorus'' in the subfamily Diplaziopsidoideae of a very broadly defined family Aspleniaceae, equivalent to the suborder Aspleniineae in PPG I.

Distribution and habitat

''Homalosorus pycnocarpos'' is endemic to eastern North America. It is widespread from southern Ontario to the Gulf of Mexico and west to Minnesota and Arkansas. It grows in moist ( mesophytic) woods and ravines in neutral or basic soils, at elevations of .

References

External links