Haplomitriopsida

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Haplomitriopsida
Temporal range: Early Permian–Recent
Haplomitrium hookeri
Scientific classification Edit this classification
Kingdom: Plantae
Division: Marchantiophyta
Class: Haplomitriopsida
Stotler & Stotl.-Crand.
Subgroups

See text.

Synonyms

Treubiopsida M.Stech, J.-P.Frahm, Hilger & W.Frey

Haplomitriopsida is a newly recognized

mitochondrial, and plastid gene sequences place this monophyletic group as the basal sister group to all other liverworts.[1][2][3][4] The group thus provides a unique insight into the early evolution of liverworts in particular and of land plants
in general.

Description

Plants of

thallus. The bifid leaves extend like wings on either side of the midrib, or may be folded upwards and pressed close together, giving the plants a ruffled appearance. By contrast, Haplomitrium grows as a subterranean rhizome with erect leafy stems. The thin, rounded leaves are arranged around the upright stems, giving the appearance of a soft moss. The species Haplomitrium ovalifolium of Australia often has bifid leaves that are asymmetrical, somewhat like those in Treubia.[5]

Haplomitrium has a number of unique characters that distinguish it from other liverworts, such as lacking rhizoids. The vegetative stems possess a central

plasmodesmata.[6] This central strand is surrounded by a cylinder of cells that conduct food throughout the plant. Such an arrangement is evocative of the xylem and phloem found in vascular plants. Although some thalloid liverwort species in the Pallaviciniaceae also possess a central conducting strand,[7] Haplomitrium differs in having a food-conducting layer and in producing no callose
.

Treubia also has features that differ from those found in other bryophytes,[8] such as the differentiation of five identifiable zones in the stem midrib. Unlike other leafy species, the oil bodies in its cells are restricted to certain clusters of cells, as they are in the Marchantiopsida. These oil body clusters appear as dark spots in the leaves when the plant is held up to the light.[9]

Diversity

Living representatives of the group exhibit an essentially

subcontinent to Asia, then spread across the Bering Strait into North America.[10]

Most species in the Haplomitriopsida are found in south of the equator, though there are northern ones. The genus Treubia is restricted to the southern hemisphere, while Apotreubia has one species in New Guinea and another disjunct between eastern Asia and British Columbia. The genus Haplomitrium exhibits a wider distribution, with species in both North and South America, northern and central Europe, the Himalayas, Japan, and Australasia.

Classification

Class Haplomitriopsida includes two orders, each with one family. The group as a whole comprises fifteen species in three genera. A fourth genus, Gessella, is known only from Permian fossils. The orders, families, and genera are as follows:

  • Subclass
    Haplomitriidae
    Stotler & Crand.-Stotl.
    • Order
      Calobryales
      Campbell ex Hamlin 1972 [Haplomitriales Buch ex Schljakov 1972]
  • Subclass
    Treubiidae
    Stotler & Crand.-Stotl.
    • Order
      Treubiales
      Schljakov 1972

An additional fossil

Treubiites kidstonii previously has been compared to the extant genus Treubia. However, upon re-examination of the material, specimens were determined to be more like Blasia and not at all to resemble Treubia as previously thought.[11] Accordingly, Treubiites is now assigned to the Blasiales
rather than the Haplomitriopsida.

References

  1. ^ Heinrichs, Jochen; S. Robbert Gradstein; Rosemary Wilson; Harald Schneider (2005). "Towards a natural classification of liverworts (Marchantiophyta) based on the chloroplast gene rbcL". Cryptogamie Bryologie. 26 (2): 131–150.
  2. S2CID 86082381
    .
  3. S2CID 85912159
    .
  4. S2CID 85788756
    .
  5. ISBN 0-914868-20-9
    .
  6. ^ Bartholomew-Began, Sharon E. (1991). "A morphogenetic re-evaluation of Haplomitrium Nees (Hepatophyta), Jumgermanniopsida)". Bryophytorum Bibliotheca. 41.
  7. ^ Hébant, C. (1977). "The conducting tissues of bryophytes". Bryophytorum Bibliotheca. 10.
  8. PMID 21642142
    .
  9. ^ Allison, K. W.; John Child (1975). The Liverworts of New Zealand. Dunedin, NZ: University of Otago Press. pp. 232–233.
  10. ISBN 49381633045
    .
  11. ISBN 0-914868-20-9
    .

External links

Data related to Haplomitriopsida at Wikispecies

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