This document discusses the peristome teeth structures found in mosses. It begins by defining the peristome as a teeth-like projection surrounding the capsule mouth in mosses. It then describes the different types of peristome teeth structures found across moss species, including orthodontous and nematodontous types. The document outlines the key characteristics and classifications of different peristome structures such as diplolepidous and haplolepidous types. It concludes by explaining the main functions of peristome teeth in allowing for gradual spore discharge from the capsule.

1. PERISTOME TEETH IN MOSS
Deboshree Das
Roll No.- 11
3rd sem BOTANY

2. Introduction
• Peristome derived from greek word – ‘peri’ meaning
‘around’ or ‘about’ and ‘stoma’, meaning ‘mouth’.
• The peristome is a teeth-like projection that surrounds
the mouth of capsule in most of the members of
Bryidae (Mosses) of Bryophytes. So, it is an important
characteristic of the Bryopsida.
• The peristome teeth spring from the rim or diaphragm.
The peristome teeth are triangular two-ply structures
which operate like trap-doors.
• The peristome is different in morphology across
species and is used as a classification tools.

3. Cont..
• In mosses, the peristome is a specialized
structure in the sporangium that allows for
gradual spore discharge.
• The teeth may be solid cellular tissue or
composed only of thickened portion of the cell
walls of adjacent cells.

4. On the basis of absence and presence of
peristome teeth ,mosses are classified into two
types
• Stegocarpous – The bryidae in which apical
portion of the capsule differentiates into
operculum and peristome.
• Cleistocarpous – In few genera of the true
mosses,both operculum and peristome teeths
are absent.

5. Structure of Peristome

7. Types Of Peristome
• Mainly two types :
 Orthodontous - Each tooth of the arthrodontous peristome type
is composed of periclinal (tangential) cell wall remnants between
two of the three concentric peristomial cell layers: the outer,
primary, and inner peristomial layers (OPL, PPL, and IPL). Often, a
double ring of teeth is present surrounding the capsule mouth . The
external ring of teeth is formed by the tangential walls between the
OPL and PPL; it is collectively known as the exostome. The internal
row consists of the cell wall remnants located between the cell
rings of the PPL and IPL, therefore the row of segments is known
as endostome.
 Nematodontous - In nematodontous peristome, the teeth of
peristome are solid composed of bundles of dead cells. It is found in
Polytrichum, Pogonatum etc.

8. Structures

9. • Depending on the number of cell columns articulated to form the
length of a tooth, two primary types of arthrodontous peristomes
are known: diplolepidous and haplolepidous.
• In haplolepidous peristomes the exostome is missing, but the
endostome is well developed and strongly thickened. The outer
surface of an endostome segment is made up of just one column of
cells from the PPL (Figure 2C). The haplolepidous peristome is
characteristic of the Grimmiales, Seligeriales, Archidiales, Pottiales,
and Dicranales.
• In diplolepidous peristomes two columns of adjacent OPL cells
participate in the formation of an exostome tooth (Figure 2B, D, E).
A medial vertical line marking the two cells can be observed along
the outer surface of each tooth. This type of peristome can be
observed in taxa of the Funariales, Bryales and Hypnales, among
others.

10. • Two basic peristome "types" have long been recognized in the
diplolepidous mosses: diplolepidous-opposite, and diplolepidous-
alternate. In diplolepidous peristomes usually both the exostome
and the endostome are present, but in several families the
endostome is lacking or reduced. When the two concentric rows
are present, each external tooth can be directly opposite or
alternated to the internal segments of the endostome.
• In the diplolepidous-opposite or "Funaria type", the anticlinal walls
of the IPL and PPL are almost perfectly aligned (co-radial), so the
endostome segments and the exostome teeth are opposite each
other. This peristome organization in found in the Funariales.
• In the diplolepidous-alternate or "Bryum type", anticlinal cell
divisions in the IPL are asymmetric, producing narrow cells adjacent
to large cells. Later in development, the IPL ring shifts displacing the
position of radial IPL cell walls relative to those in the PPL cells. This
results in the placement of the endostome segments alternating
with the exostome teeth. The diplolepidous alternate peristome is
common in the Bryales, Rhizogoniales, Hookeriales, and Hypnales.

11. Figure : The different peristome types of Bryopsida.
A. Cross section of an embryonic sporophyte capsule.
B. Diplolepidous opposite peristome (Funaria type).
C. Haplolepidous peristome (Dicranum type).
D. Diplolepidous alternate (Orthotrichum type).
E. Diplolepidous alternate (Bryum type).

12. Functions
• Peristome teeth serve as a valve that allows the spores
to exit the capsule. The peristome teeth open and
splay outward during times of low humidity, allowing
the spores to float away and disperse. One layer readily
absorbs and releases water, while the other layer does
not react very much to varying humidity levels. This
causes the teeth to bend outward during times of low
humidity.
• Some peristome teeth work in other ways; example,
Funaria mosses have slits between the teeth that
expand during dry periods. In other mosses, such as
Polystrichum mosses, the peristome teeth do not
respond to moisture.

13. References

14. Thank you