Trichostomum

Trichostomum crispulum, photographed by Hermann Schachner.

Belongs within: Pottiaceae.

Trichostomum is a genus of mostly tall, relatively robust mosses (Dixon 1924).

Define ‘Trichostomum
Published 12 August 2017

The moss in the photo at the top of this post generally goes by the name of Trichostomum crispulum. Trichostomum is a cosmopolitan genus in the Pottiaceae, the largest recognised family of mosses with about 1500 species overall. But with great diversity comes great difficulty of identification. Pottiaceae tend to be small mosses that are common in harsh habitats. Features of pottiaceous mosses are often hard to distinguish and may be quite variable, making it difficult to confidently define taxa. As a result, Pottiaceae is a prime example of what I like to call ‘taxonomic blancmange’: something that tends to just get prodded nervously then backed away from when it wobbles ominously.

Characteristic features of Trichostomum as it is commonly recognised tend to include symmetric leaves with more or less plane margins, and with the basal cells of the leaf differentiated straight across the blade or in a U-shape. The peristome of the capsule also tends to be short and straight, and the sexual system is usually dioicous (with separate male and female plants) (Flora of North America). However, none of these features are entirely reliable, and some species have been the subject of extensive disagreement about whether they should be placed in Trichostomum, or in a related genus such as Weissia or Tortella.

To date, only a selection of Pottiaceae species have been subject to molecular analysis, but these analyses have confirmed the unsatisfactory nature of the current system. A molecular phylogenetic analysis of the pottiaceous subfamily Trichostomoideae by Werner et al. (2005) did not identify Trichostomum species as a monophyletic clade; instead, various representatives of the ‘genus’ were scattered throughout the subfamily. The type species of Trichostomum, T. brachydontium, was associated with a few close relatives such as T. crispulum in a broader clade containing numerous species of the genus Weissia. As a result, it has been suggested that the two genera should perhaps be synonymised, in which case the name Trichostomum would be absorbed by the older Weissia. But first, someone would need to work out just how such a genus could be recognised…

Systematics of Trichostomum

Characters (from Dixon 1924): Plants for the most part tall, rather robust; leaves usually narrow, elongate, with lax, pellucid, or hyaline basal cells, and minute, obscure, papillose upper areolation, curled and often strongly cirrate-incurved when dry. Capsule oblong or cylindrical, peristomate, teeth slender, divided to or nearly to base into two filiform division, more or less imperfect, or long, erect, oblique or contorted. Dioicous.

<==Trichostomum Bruch in Müll. 1829S04
    |  i. s.: T. austrocrispum (Beckett) Zander 1993 (see below for synonymy)SK02
    |         T. bombayenseN02
    |         T. brachydontium Bruch in Müll. 1829S04 (see below for synonymy)
    |         T. diminutum [=Timmiella diminuta]SK02
    |         T. eckelianum Zander 1993 (see below for synonymy)SK02
    |         T. hibernicum (Mitt.) Dixon 1896S04 (see below for synonymy)
    |         T. leptotheca Müll.Hal. 1868 (n. d.)SK02
    |         T. sublamprotheciumJ87
    |--T. subg. Crispuliformia (Kindb.) Zander 1993 [=T. subg. Crispuliformes]OZB-O03
    |    `--T. crispulum Bruch in Müll. 1829OZB-O03, S04 (see below for synonymy)
    `--T. subg. Oxystegus (Lindberg ex Limpricht) Ochyra in Ochyra, Żarnowiec & Bednarek-Ochyra 2003 (see below for synonymy)OZB-O03
         `--T. tenuirostre (Hook. & Taylor) Lindb. 1884OZB-O03, S04 (see below for synonymy)
              |--T. t. var. tenuirostreD24
              |--T. t. var. daldinianumD24
              |--T. t. var. gemmiparum (Schimp.) Zander 1978S04
              `--T. t. var. holtii (Braithw.) Dixon 1896S04 [incl. Mollia terrenaD24]
Nomina nuda: Trichostomum albovaginatum Hampe ex Müll.Hal. 1901SK02
             Trichostomum weymouthii Müll.Hal. 1901 [=Desmatodon weymouthii Watts & Whitel. 1902]SK02

Trichostomum austrocrispum (Beckett) Zander 1993 [=Weissia austrocrispa (Beckett) Stone 1980; incl. Pleuridium lanceolatum (R.Br.bis) Paris 1898]SK02

Trichostomum brachydontium Bruch in Müll. 1829S04 [=Mollia brachydontiaD24; incl. Tortella aristatula Broth. ex Watts & Whitel. 1902 (n. n.)SK02, Tr. aristatulum Broth. 1916SK02, Mollia compressaD24, Tr. mutabile var. cophocarpumD24, S04, Tr. episemumD24, Mollia intumescensD24, M. littoralisD24, Trichostomum mutabile var. littoraleD24, S04, M. lutescensD24, Tr. mutabileS04]

Trichostomum crispulum Bruch in Müll. 1829S04 [=Didymodon crispulus non Didimodon crispulus Hook.f. & Wilson 1844OZB-O03, Mollia crispulaD24; incl. Trichostomum crispulum var. angustifoliumD24, T. crispulum var. brevifolium (Sendtn. ex Müll.Hal.) Bruch & Schimp. in Bruch, Schimp. & Gümbel 1843S04, OZB-O03, T. crispulum var. elatumS04, T. crispulum var. longifoliumD24, T. crispulum var. nigrovirideS04, Mollia scaphoideaD24, T. crispulum var. viridulumS04]

Trichostomum eckelianum Zander 1993 [incl. Tortella cirrhata Broth. 1902, Tr. cirrhatum (preoc.), To. subflavovirens Broth. & Watts 1915]SK02

Trichostomum hibernicum (Mitt.) Dixon 1896S04 [=Mollia hibernicaD24, Oxystegus hibernicusS04, Tortula hibernicaD24; incl. Barbula cirrifoliaD24]

Trichostomum tenuirostre (Hook. & Taylor) Lindb. 1884S04 [=Weisia tenuirostrisD24, Mollia tenuirostrisD24, Oxystegus tenuirostrisS04; incl. *Oxystegus cylindricusOZB-O03, Tortella cylindricaOZB-O03]

Trichostomum subg. Oxystegus (Lindberg ex Limpricht) Ochyra in Ochyra, Żarnowiec & Bednarek-Ochyra 2003 [=T. [unranked] Oxystegus Linderg ex Limpricht 1888]OZB-O03

*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.

[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.

[N02] Negi, H. R. 2002. Abundance and diversity of moss communities of Chopta-Tunganath in the Garhwal Himalaya. Journal of the Bombay Natural History Society 99 (3): 418–433.

[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.

Werner, O., R. M. Ros & M. Grundmann. 2005. Molecular phylogeny of Trichostomoideae (Pottiaceae, Bryophyta) based on nrITS sequence data. Taxon 54 (2): 361–368.

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