Belongs within: Dicranaceae.
Dicranum is a genus of mosses found primarily in temperate and arctic parts of the Northern Hemisphere, with a few species found on tropical mountains. The genus name comes from the Greek word dikranon, a pitchfork, and refers to the split teeth in the peristome (N. Klazenga). Species are often distinguished by characters of the leaf cross sections. The leaf nerve is contained in a section of differently formed cells with median guide-cells in species of the subgenera Eu-Dicranum and Aporodictyon but such cells are absent in members of the subgenus Arctoa (Dixon 1924).
Pitchfork mosses
Published 23 July 2013
The subject of today’s post is the cosmopolitan moss genus Dicranum, sometimes known as fork mosses or, apparently, wind-blown mosses. Dicranum species are characterised by elongate narrow leaves and an erect, often forked growth habit. In some habitats, Dicranum species may form reasonably extensive turfs. The genus name comes from the Greek word for a pitchfork and apparently refers to the teeth of the peristome (the ring of teeth around the opening of the spore capsule) though, if this is true, naming these mosses after a feature of the spore capsule may not necessarily have been the best idea. Many Dicranum populations produce sporophytes relatively rarely. Instead, these populations more commonly reproduce asexually through the production of vegetative propagules by the gametophyte. Once such species, the Holarctic Dicranum flagellare, produces terminal clusters of reduced branches, called ‘brood branches’. If detached from the parent plant, these brood branches can grow into a new moss. A notable dispersal agent for brood branches, as it turns out, is slugs (Kimmerer & Young 1995). Brood branches break off the parent plant as the slug crawls past them, adhering to the slug by means of its slime. The trail of slime left by the slug also greatly improves the chance of a brood branch adhering to a suitable substrate once it becomes separated from its transport.
Because of the rarity of sporophytes, species of Dicranum are mostly distinguished by features of the leaves. Dicranum leaves may be straight or curved, the edge of the leaf may be smooth or toothed, and the blade of the leaf may be composed of one or two cell layers. Many species are characterised by the shape of the leaf in transverse section (Hedenäs & Bisang 2004). When sporophytes are produced, Dicranum species are dioicous: that is, they have separate male and female plants. However, in a number of species, the male plants are reduced in size and grow epiphytically on the leaves or rhizoids of the larger female plants. At least one species, Dicranum scoparium, has both dwarf and full-sized males (Hedenäs & Bisang 2004). Some Dicranum species have wide distributions, with a number found almost throughout Eurasia and North America, but others have more restricted distributions (D. transsylvanicum, for instance, is known from a single location in western Romania). Dicranum species are often very selective habitat-wise, with species differing in their choice of habitat, and they have been used as indicators of environmental conditions. This habitat selectivity can result in fragmented species distributions: for instance, Dicranum muehlenbeckii (which grows in dry, calcareous or mineral-rich environments) is found in central Europe, but is also known from a single locality in central Sweden. Dicranum scoparium, a more generalist species found in both humid and dry conditions, is widespread in Eurasia and North America, but is also known from New Zealand and a single region of Australia, near Mt Kosciuszko in New South Wales. Much ink has been spilled as regards the biogeographic processes underlying disjunct distributions in moss taxa. In that light, it should be pointed out that, while Australian and New Zealand specimens of Dicranum scoparium do tend to be less robust than the average Holarctic specimen, no molecular differences have yet been identified between the populations (Klazenga 2012).
Systematics of Dicranum
Characters (from Smith 2004): Dioicous. Female plants usually robust, male plants minute or of similar size to female plants. Leaves erect to falcate-secund, from ovate or lanceolate basal part tapering to acuminate apex; margins usually plane, frequently dentate or denticulate above; costa ending below apex to excurrent; in section usually with one or two stereid bands; cells incrassate, porose or not, basal linear or narrowly rectangular, becoming narrowly rectangular to quadrate above, mamillose or not. Setae straight, capsules erect or inclined, straight or curved, not strumose, often more or less striate; peristome teeth reddish, divided to about halfway into two unequal segments, pitted-striolate below, papillose above; lid rostrate; calyptrae cucullate.
<==Dicranum Hedw. 1801SK02 |--D. subg. DicranumS04 | |--D. sect. DicranumS04 | | |--D. bonjeanii De Not. 1837S04 (see below for synonymy) | | | |--D. b. var. bonjeaniD24 | | | |--D. b. var. calcareumD24 | | | `--D. b. var. rugifoliumD24 | | |--D. leioneuron Kindb. 1889S04 | | |--D. majus Turner 1804S04 (see below for synonymy) | | |--D. molle [incl. D. arcticum, D. hypselum]D24 | | |--D. polysetum Sw. 1801S04 (see below for synonymy) | | `--D. scoparium Hedw. 1801D24, SK02 (see below for synonymy) | |--D. sect. Convolutifolia (Kindberg) Ochyra in Ochyra, Żarnowiec & Bednarek-Ochyra 2003 (see below for synonymy)OZB-O03 | | |--D. muehlenbeckii Bruch & Schimp. in Bruch, Schimp. & Gümbel 1847 [incl. D. bambergeri]OZB-O03 | | | |--D. m. var. muehlenbeckiiOZB-O03 | | | `--D. m. var. cirrhatum (Schimp.) Lindb. in Norrl. 1878OZB-O03 | | `--D. spadiceum Zetterst. 1865OZB-O03 (see below for synonymy) | |--D. sect. Crassinervia Roth 1904S04 [incl. D. subg. Crassidicranum Limpr. 1886OZB-O03] | | |--D. fulvum Hook. 1819OZB-O03 | | |--D. scottianum Turner 1904S04 [=Orthodicranum scottianumS04; incl. D. scottiiD24, D. subnitescensD24] | | `--D. viride (Sull. & Lesq.) Lindb. 1863OZB-O03 [=Campylopus viridisD24] | |--D. sect. Elongata Hagen 1914S04 | | |--D. elongatum Schleich. ex Schwägr. 1811S04 (see below for synonymy) | | |--D. groenlandicum Brid. 1819 [incl. D. elongatum var. orthocarpum, D. tenuinerve]OZB-O03 | | `--D. sendtneri Limpr. 1886OZB-O03 | |--D. sect. Fuscescentiformia Kindberg 1897S04 [=D. sect. Fuscescentia Nyholm 1953 (nom. inv.)OZB-O03] | | |--D. (sect. *F.) fuscescens Turner 1804OZB-O03, S04 (see below for synonymy) | | | |--D. f. var. fuscescensD24 | | | `--D. f. var. falcifoliumD24 | | `--D. flexicaule Brid. 1826S04 (see below for synonymy) | `--D. sect. Spuria Bruch & Schimp. in Bruch, Schimp. & Gümbel 1847S04 | |--D. acutifolium (Lindb. & Arnell) Jensen in Weimarck 1937OZB-O03 | |--D. bergeri Blandow in Sturm 1805[incl. D. affine]S04 | |--D. spurium Hedw. 1801S04 | `--D. undulatum Schrad. ex Bridel 1801 [=D. schraderi Wahlenberg 1806; incl. D. fastigiatum]OZB-O03 `--D. subg. Orthodicranum Bruch & Schimp. in Bruch et al. 1851S04 [=Orthodicranum (Bruch & Schimp.) Loeske 1910OZB-O03] |--D. flagellare Hedw. 1801S04 [=Orthodicranum flagellare (Hedw.) Loeske 1910OZB-O03] |--D. montanum Hedw. 1801S04 (see below for synonymy) `--D. tauricum Sapjegin 1911S04 (see below for synonymy) Dicranum incertae sedis: D. aciphyllumD03 D. australeD03 D. billardieriD03 D. cirrhifolium Schpr. ex Dusén 1903D03 D. dicranellatum Dusén 1903D03 D. fragilifoliumD24 D. frigidumJ87 D. hariotiD03 D. imponensD03 D. laticostatumD03 D. leucopterumD03 D. macropusD03 D. nigricauleD03 D. ‘novae-hollandiae’ Hornsch. ex Cardot 1908 (preoc.)SK02 D. orthocomum [=Campylopus orthocomus]D03 D. pumilumD03 D. racovitzaeD03 D. ramulosumD03 D. scaberrimum Dusén 1903 [=Campylopus scaberrimus ms]D03 D. sumichrastiJ87 D. toniniD03 Nomina nuda: Dicranum capillifolium Broth. in Dusén 1903D03 Dicranum chloracaulon Müll.Hal. ex Muell. 1880SK02 Dicranum flavifolium Müll.Hal. ex Muell. 1880SK02 Dicranum geheebii Müll.Hal. ex Muell. 1880SK02 Dicranum grandialare Dusén 1903D03 Dicranum limbatum Broth. ex Müll.Hal. 1901 [=Dicranoloma limbatum Watts & Whitel. 1906, Leucobryum limbatum Broth. ex Wijk, Margad. & Florsch. 1964, Leucoloma limbatum Broth. ex Watts & Whitel. 1902]SK02 Dicranum percompactum Dusén 1903D03 Dicranum perremotifolium Dusén 1903D03 Dicranum peruncinatum Dusén 1903D03 Dicranum sordideviride Müll.Hal. ex Geh. 1876 [=Dicranoloma sordideviride Watts & Whitel. 1906]SK02 Dicranum subviride Mitt. 1882SK02 Dicranum walteri Hampe ex Mitt. 1882 [=Dicranoloma walteri Watts & Whitel. 1906]SK02
Dicranum sect. Convolutifolia (Kindberg) Ochyra in Ochyra, Żarnowiec & Bednarek-Ochyra 2003 [=D. [unranked] Convolutifolia Kindberg 1898, D. sect. Muehlenbeckia Peterson ex Nyholm 1987 (nom. illeg.)]OZB-O03
Dicranum bonjeanii De Not. 1837S04 [incl. D. interludensD24, D. bonjeanii var. juniperifoliumOZB-O03, D. palustre var. juniperifoliumOZB-O03, D. palustreD24, D. bonjeanii var. polycladumOZB-O03]
Dicranum elongatum Schleich. ex Schwägr. 1811S04 [incl. D. elongatum var. flagelliferumOZB-O03, D. elongatum var. longifolium non D. longifoliumOZB-O03, D. elongatum var. polycladum non D. bonjeanii var. polycladumOZB-O03, D. elongatum var. robustum non D. robustum OZB-O03, D. sphagniSK02]
Dicranum flexicaule Brid. 1826S04 [=D. congestum var. flexicauleOZB-O03, D. fuscescens var. flexicauleD24; incl. D. fuscescens var. congestumD24, OZB-O03, D. fagimontanumOZB-O03]
Dicranum fuscescens Turner 1804OZB-O03, S04 [incl. D. bergeri var. compactumD24, D. fuscescens var. compactumOZB-O03, D. fergussoniD24, D. fuscescens var. longirostreOZB-O03, D. fuscescens var. robustum nec D. robustum nec D. elongatum var. robustumOZB-O03, D. fuscescens f. subalbescensOZB-O03]
Dicranum majus Turner 1804S04 [incl. D. majus var. orthophyllum nec D. scoparium var. orthophyllum Brid. 1806 nec D. longifolium var. orthophyllumOZB-O03]
Dicranum montanum Hedw. 1801S04 [=Orthodicranum montanum (Hedw.) Loeske 1910OZB-O03; incl. O. montanum var. polycladonOZB-O03, Dicranum montanum var. pulvinatum non D. pulvinatumOZB-O03]
Dicranum polysetum Sw. 1801S04 [incl. D. rugosumS04, D. undulatum Ehrh. ex Weber & Mohr 1803 non Schrad. ex Bridel 1801OZB-O03]
Dicranum scoparium Hedw. 1801D24, SK02 [incl. D. goeppertianumOZB-O03, D. scoparium var. curvulumOZB-O03, D. scoparium var. orthophyllum Brid. 1806OZB-O03, SK02, D. scoparium var. paludosumOZB-O03, D. scoparium var. recurvatumOZB-O03, D. tectorumOZB-O03, D. scoparium var. turfosumOZB-O03]
Dicranum spadiceumOZB-O03 [=D. scoparium var. spadiceumD24; incl. D. scoparium var. alpestre non D. alpestreD24, D. neglectumOZB-O03]
Dicranum tauricum Sapjegin 1911S04 [=Orthodicranum tauricum (Sapjegin) Smirnova 1970OZB-O03, incl. D. strictumS04, O. strictumS04]
*Type species of generic name indicated
References
[D24] Dixon, H. N. 1924. The Student’s Handbook of British Mosses 3rd ed. V. V. Sumfield: Eastbourne.
[D03] Dusén, P. 1903. Patagonian and Fuegian mosses. In: Scott, W. B. (ed.) Reports of the Princeton University Expeditions to Patagonia, 1896–1899 vol. 8. Botany pp. 63–126. The University: Princeton (New Jersey).
Hedenäs, L., & I. Bisang. 2004. Key to European Dicranum species. Herzogia 17: 179–197.
[J87] Judd, W. S. 1987. Floristic study of Morne La Visite and Pic Macaya National Parks, Haiti. Bulletin of the Florida State Museum—Biological Sciences 32 (1): 1–136.
Kimmerer, R. W., & C. C. Young. 1995. The role of slugs in dispersal of the asexual propagules of Dicranum flagellare. The Bryologist 98 (1): 149–153.
[OZB-O03] Ochyra, R., J. Żarnowiec & H. Bednarek-Ochyra. 2003. Census Catalogue of Polish Mosses. Institute of Botany, Polish Academy of Sciences: Cracow.
[S04] Smith, A. J. E. 2004. The Moss Flora of Britain and Ireland 2nd ed. Cambridge University Press.
[SK02] Streimann, H., & N. Klazenga. 2002. Catalogue of Australian Mosses. Flora of Australia Supplementary Series 17. Australian Biological Resources Study: Canberra.