Overview

Brief Summary

Introduction

The tropical moss Leiomitrium plicatum is a rare species restricted to Indian Ocean islands.It is the only member of the genus Leiomitrium, which belongs to the family Orthotrichaceae.
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Comprehensive Description

Relatives

Diagnostic Description
Leiomitrium plicatum is a very distinctive species. It is distinguished from other members of the Orthotrichaceae family by the combination of:
  • a creeping habit
  • obtuse leaves of the lower branches
  • papillose upper leaf cells


Closely-related genera:
Leiomitrium is considered most closely related to the genus Macrocoma, however more research needs to be undertaken into the phylogenetic relationships of the Orthotrichaceae family.

Distinguishing Leiomitrium from Macrocoma
Macrocoma has:
  • Always acute leaves (compared to obtuse)
  • Smooth upper leaf cells (compared to papillose), as seen under the microscope


Distribution differences:
  • Leiomitrium is restricted to Indian Ocean islands
  • Macrocoma is more widespread, but also occurs on the Indian Ocean islands
  • Orthotrichum and Ulota can be commonly encountered in temperate regions of the world, such as Europe and North America
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Distribution

Distribution habitat

Habitat
Leiomitrium plicatum is restricted to tropical oceanic islands where it grows on trees or rocks. More information is still required about its ecology.

Distribution
Leiomitrium plicatum occurs on the Mascarene Islands of:
  • Réunion
  • Mauritius
  • Rodrigues
This species was originally described from a specimen collected from Mauritius some 200 years ago. However, there are no published records of Leiomitrium plicatum on this island post 1900.In 2008, a fieldwork expedition to Réunion enabled further documentation of the distribution of Leiomitrium on this island.

Conservation status
Leiomitrium plicatum has a very restricted global distribution and information about its abundance is limited. More data is needed to accurately access whether populations are stable, decreasing or increasing. The continued occurrence of this species on Mauritius and Rodrigues needs to be verified.

Threats
The major threat to Leiomitrium plicatum is considered to be habitat loss due to urban development.
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Physical Description

Morphology

Leiomitrium plicatum:
  • Forms mats of creeping stems with numerous short branches
  • Is yellow-brown to green in colour
  • Is dioicous
Branch leaves:
  • Closely appressed to the stem when dry but spread out when wet
  • Vary in shape from lanceolate to broadly oblong with a rounded leaf tip
  • 0.8-1.5mm long
Upper leaf cells:
  • Irregularly rounded and bulging
  • 1-3 papillae per cell
Cells at the base of the leaf:
  • Rounded in shape
  • Either smooth or have 1 papilla per cell
Thickened midrib of the leaf:
  • Broad
  • Ends below the leaf tip
Leaves arising from the creeping stem: Slightly different to the branch leaves, with:
  • more pointed tips
  • cells either smooth or with only 1 papilla
Setae (the stalks to which capsules are attached):
  • Stout
  • Sheathed by a long cup-shaped structure (ochrea)
Capsules:
  • Cylindric
  • 8 groves
  • 2 layers of peristome
Calyptrae (protective caps covering capsules):
  • Relatively large
  • Mitrate (shaped like a bishop’s miter)
  • Hairy
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