A Pictorial Representation of Peristomal Architecture

2006·1.8 MB·English

by  Chris, Gibson Tyshing

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Bryophytespecialissue
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A
pictorial representation ofperistomal architecture
Chris Tyshing and Maria Gibson
PlantEcologyResearchUnit,SchoolofLifeandEnvironmentalSciences
DeakinUniversity,221BurwoodHighway,Burwood, Victoria3125
Abstract
The terminology associated with the use ofperistomes in the identification and classification of
mosses is cumbersome and difficult to understand. This paper provides a pictorial explanation of
peristomal architecture with its associated terminology, such as nematodontous and arthrodontous
peristomes, and the division ofthe latter into diplolepideous and haplolepideous peristomes. (The
VictorianNaturalist 123(4),2006,203-211
The moss plant normally seen and recog- hygroscopic movement in response to
nised is referred to as a gametophyte as it changes in humidityby bendingbackwards
produces the gametes, i.e. egg and sperm. and forwards (Proctor 1984). The move-
When the sperm fertilizes the egg a sporo- ment provides a gentle catapulting action
phytedevelops. Thesporophyteisephemer- for launching spores a short distance into
al and essentially remains dependent on its the air, where they may be caught by a
gametophyte parent (Fig. 1), i.e. nutrients gentle breeze and dispersed to an environ-
are obtained from the gametophyte parent ment suitable for germination. Subsequent
through the basal foot ofa stalk-like struc- to germination, spores will develop into
ture (the seta) that remains embedded with- another gametophyte generation.
in the parental gametophytetissue. A spore Hygroscopic movement of the exostome
capsuleterminatesthisseta(Fig. 1). may be particularly relevant in closed for-
Many mosses have one or more rings of est situations where opportunities for air-
teeth around themouthofthe capsule (Fig. transport ofspores needs to be maximized.
2). The teeth collectively are referred to as The inner ring ofteeth (endostome) (Fig.
the peristome (Fig. 1) and are protected by 2) may regulate spore dispersal bygradual-
an operculum or lid (Fig. I), which falls ly siftingthespores.
offwhen the spores are mature. However, As spore dispersal mechanisms in moss-
notall mosseshaveperistomes. es,peristomes are specialised, intricate and
The outer ring of teeth (exostome) in architecturally elaborate. Adaptive trends
double peristomes (Fig. 2) may exhibit ofmorphological characters have resulted
Vol. 123 (4) 2006 203
Bryophytespecialissue
sFipgo.ro1p.hyCtoelo(snpy) boefarToirntgilalamaatnutraercctaipesaul(eHa(cm)pete)rmWiinlastoinn.g aLesaeftay(gsea)m.eAtoppheryitseto(mge)(wpi)thofdleopnegndteeentth
occurs atthe mouthofthecapsule. Thisperistome initially iscoveredbyan operculum(o)which is
shedwhensporesbecomemature. Scalebaris3.5 mm.
tFhiea.e2x.o.sCtaopmseul(eex()c,)aonfdHaynpinnunemrcruopwreosfsitefeotrhm,ethHeeednwd.oswittohmepe(rein)s.toSmpeor(ep)ss(shpo)w.iSncgalaenboauiteisr2r0o0wpomt.teeth,
TheVictorian Naturalist
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Bryophytespecialissue
Fig. 3.. Nematodontous teeth (nt) ofAtrichumandrogymim(Mull. Hal.) A.Jaeger. Teeth are made
up oflayers (1) ofwhole cells. Tips ofteeth attach to the disc-likeepiphragm (e). Slight air move-
mentcausesreleaseofsporesbetweentheteeth. Capsule(c). Spores(sp).Scalebaris K)0pm.
in different peristomal configurations that a disc-like epiphragm that releases spores
have been usedas importanttools in higher with the help of a little air movement. In
level classification ofmosses for over 150 essence, spores are released via a pepper
years(Vitt 1999).Threeperistomal charac- shaker effect. Dawsonia superha Grev.
ters are vital to classification. These are var. pulchra (Fig. 4) shows another
cell structure ofthe teeth, the arrangement method of spore dispersal where the
ofthe outerteeth relative to the innerteeth nematodontous teeth take the form ofmul-
(where present), i.e. whether the outer ticellular filaments forming a twirled
teeth are alternate or opposite the inner 'brush’. When the spores mature, the
teeth, and the initial cell alignment 'brush’ untwists, allowing gradual release
(Goffinetetal. 1999). ofthespores.
In the first instance, peristomesaredivided Arthrodontous peristomes have teeth
into two types, nematodontous and composed ofthickened cell wall remnants
arthrodontous peristomes. In terms ofperis- ofsquat cells occurring in two orthreecell
tomal architecture, this division is as impor- layers (Crum 2001) involving the outer,
tantasthedivisionbetweenmonocotyledons primary and inner peristome layers, i.e.
and dicotyledons in flowering plants, OPL, PPL, and IPL respectively. This
although thedistinction isata lowerclassifi- means that during development of the
catorylevelforthemossesthan forthe flow- teeth, cell wallplates located parallel tothe
eringplants. capsule rim (periclinal), become differen-
Nematodontous peristomes have teeth tially thickened, while much ofthe cross-
composed of whole, dead and ‘mostly wall and radiallyvertical cell wall material
elongate cells in one or more layers’ perpendicular to the capsule rim (anticli-
(Crum 2001) with walls thickened uni- nal) becomes reabsorbed (Buck and
formly (Shaw et al. 1989). However, Goffinet 2000). Ninety percent of true
arrangement of the cells can vary from mosses are classified as arthrodontous
ospfewciheosletoceslplesciwehsi.chFigoucrceur3indentaeimlastoladyoenr-s (CArrutmhr2o0d0o1n)t.ous peristomes are further
tous teeth. In the species depicted, divided into diplolepideous and haplolepi-
Atrichum anclrogynum (Mull. Hal.) A. deous peristomes. Diplolepideous peris-
Jaeger, the tips ofthe teeth are attached to tomes usually have a double layer ofteeth,
Vol. 123 (4) 2006 205
Bryophytespecialissue
Fig. 4. The brush-like nematodontous teeth (nt) ofDawsonici superba Grev. var. pulchrq Zanten
facilitatessporereleaseasituntwists. Capsule(c).Spores (sp). Scalebaris50pm.
the exostome forming the outer teeth and endostome consists ofthis basal membrane
theendostome formingthe innerteeth. It is with 16 teeth (also referred to as segments)
the outer row that is ofvital importance to which arc keeled, perforated and alternate
classification,principallybecausethe inner with cilia (in groups of one to four) in
row of teeth may be reduced to nothing many species(Fig.6)(Magombo2003).
more than a fragile collar-like basal mem- The exostome generally consists of 16
brane (Fig. 5). However, moretypicallythe teeth (Shaw and Renzaglia 2004), which
tFeieot.h5c.o.nsDtiiptluotlienapitdheeouesxopsetroimseto(meex).ofThGelyepxootshteocmieumissvciituarlolyidiemspo(rHtoaonkt.)toHcalmaspsei.ficsahtoiwoninagst1h6eoiuntneerr
teeth orendostome (en) may be reducedto acollar-like basal membrane, as depicted in thisfigure.
Capsule(c).Spores(sp).Scalebaris50pm.
The Victorian Naturalist
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Bryophytespecialissue
Fig. 6.. Elaborate diplolepideous peristome of Ptychomnion aciculare (Brid.) Mitt, showing exo-
stome(ex) oi 16teeth, and endostome(en)ofbasal membrane with 16 keeled teeth (also known as
segments). Perforations occuralong the upper section ofeach keel (k) and two cilia (ci) alternate
with each segment. An endostome showing a basal membrane with teeth is more typical ofa
diplolepideous peristome than the reduction ot the endostometo justacollar-like basal membrane.
Spores(sp). Scalebaris 100pm.
Fig. 7.. DiplolepideousexostometoothofHypnodendron vitienseMitt, showingtheouter face con-
sistingoftwocolumns ofpericlinal(parallel'tothecapsulerim)cell wall plates(pe)offormercells.
Thetrabeculae(tr)derived fromcross-wallsontheouterfaceofeach exostometoothandthezig-zag
median line(ml)reflectthetwocolumnsofcells that form each tooth, i.e. thetrabeculaeand medi-
an linerepresentanticlinal (perpendiculartothecapsulerim)cell wall remnantsand bordertheperi-
clinalcell wall material.Theterm ‘diplolepideous’ referstothistwincolumnformation. Snores(so)
Scalebaris20pm.
Vol. 123 (4) 2006 207
Bryophytespecial issue
thickened cellwall remnants
oftwocellsfrom OPL
thickened cellwall remnant
outertooth ofonecellfrom PPL
innertooth
Fig. 8.. Diagram ofa diplolepideous peristome (after Buck and Goffinet 2000) showing exostome
(outer teeth) and endostome (inner teeth) opposite each other. Much ofthe anticlinal cell wall
material perpendicularto the capsule (A) becomes reabsorbed. Periclinal walls (PE). Outer peris-
tomal layer(OPL). Primaryperistomal layer(PPL). Innerperistomallayer(IPL).
outer thickened cellwall
inner remnantof
tooth
tooth onecell
PPL
thickened cellwall
remnantsoftwo
OPL cellsfrom OPL
IPL
Fig. 9.. Diagram ofa diplolepideous peristome (after Buck and GoHinet 2000) showing alternate
exostome (outer teeth) and endostome (inner teeth). Much ofthe anticlinal cell wall material (A)
perpendicular to the capsule becomes reabsorbed. Periclinal walls (PE). Outer peristomal layer
(OPL). Primaryperistomal layer(PPL). Innerperistomal layer(IPL).
have an outer face oftwo columns and an Hedw., with exostometeeth alternatingwith
inner face of a single column (OPL + endostometeeth. Froman evolutionarypoint
PPL), each column consisting ofa stack of ofview, the ‘opposite’ arrangement ofthe
periclinal cell wall plates of former cells. endostomeandexostome isconsideredmore
The horizontal lines (trabeculae) derived primitive(Vitt 19.84).
from cross-walls (Fig. 7) on the outerface Haplolepideous peristomes have teeth
ofeach exostome tooth, and the zig-zag with an outer face ofone column consist-
median line, reflectthestructure ofthe two ingofwall remnants ofa stack ofcells and
columns of cells occurring side by side an inner face oftwo columns (PPL -f IPL)
(Edwards 1984; Shaw et a/. 1989). The consisting ofwall remnants oftwo stacks
term diplolepideous refers to thistwin col- ofcells. Haplolepideous peristomes usual-
umn formula(Fig. 7). ly consist ofa single layer of 16 teeth
Diplolepideous peristomesmaybe config- (Shaw and Renzaglia2004). The term hap-
ured with an ‘opposite’ peristome cell pat- lolepideous refers to the outerface consist-
tern (Fig. 8) oran ‘alternate* peristome cell ing ofwall remnants ofthe single stack of
pattern (Fig. 9), i.e. with the exostome and cells. The horizontal lines (trabeculae)
endostome teeth opposite or alternate to (Fig. 12) correspond to the top and bottom
each other respectively. Figure 10showsthe plates. Figure 13 represents the haplolepi-
exostome teeth opposite endostome teeth deous configuration. It is thought that the
while Fig. 11 showsHypnum cupressifonne haplolepideous peristome (Fig. 14) is
208 The Victorian Naturalist
Bryophytespecialissue
Fig. 10.. Funaria-typediplolepideousperistomeshowing ‘opposite’ tooth arrangement. Exostomeof
outerteeth (ex). Endostomeol innerteeth (en). Zig-zagmedian line(ml). In evolutionaryterms, the
‘opposite’ arrangementofouterand innerteeth isconsidered moreprimitivethan thealternatetooth
arrangementshown in Fig. 11. Sealebaris40pm.
Fig. II.. Diplolepideous peristome ofHypnum cupressiforme Hedw., showing ‘alternate’ tooth
arrangement. Exostomeofouterteeth (ex). Endostomeofinner teeth (en) with basal membraneand
keeled, perforated teeth (segments). Cilia alternate with segments, but arc obscured by spore mass.
Exostome teeth aretrabeculate(tr) on both theouterfaceand inner face butthe innerface is deeply
trabeculate. Capsule(c). Spores(sp).Scalebaris 100pm.
Vol. 123 (4) 2006 209
Bryophytespecialissue
Fig. 12.. Ouier face of haplolepideous teeth ofDicranoloma menziesii (Taylor) Renauld showing
trabeculae(t) reflectingthe wall material ofasinglecolumn orstackofcells that formseachtooth,
contrastingwiththetwocolumnsofdiplolepideousteethshown in Fig. 7.Thetrabeculaecorrespond
tothe top and bottom cell wall plateswhicharcanticlinal, i.e. perpendiculartothe capsule rim. The
material seen between thetrabeculae is the periclinal cell wall remnants, i.e. cell wall remnants par-
alleltothecapsulerim. Scalebaris 10pm.
thickened cell wall remnantof
onecellfrom PPL
tooth thickened cellwall remnantsof
twocellsfrom PL
I
Fig. 13.. Diagramofhaplolepideousperistome(afterBuckandGoffinet2000). Much ofthe anticli-
nal wall material (A) perpendiculartothecapsule becomesreabsorbed. Periclinal walls(PE). Outer
peristomal layer(OPL). Primaryperistomal layer(PPL). Innerperistomal layer(1PL).
derived from the diplolepideous peristome fication. Study ofthese ancient plants and
with opposite endostome and exostome, theirreproductive innovations is crucial to
and is homologous with endostomal seg- understanding the evolution of land plants
ments(BuckandGoffinet2000; Magombo (Shaw and Renzaglia2004).
2003; Newton and Cox 2000; Shaw and
Acknowledgements
RePnezraigsltioam2a0l04t;erVimtitno10l8o1g)y. does not end wWheosseincteirmeelyantdhanthkoutghehtafunloncyommomuesntresfewreee,afroer
here, but the above detail provides readers most grateful. Thanks also to Department of
with an introduction to this cumbersome Sustainability and Environment for permission
language belonging to the intricate, elabo- to collect specimens (Permit Number
rate and beautiful world of peristomal 10002309).
architecture, moss identification and classi-
210 The Victorian Naturalist
Bryophytespecialissue
Fig. 14.. Tortilla recurvata Hook, showing haplolepideous peristome (p) consisting ofbasal mem-
braneand32tubularteeth. Capsule(c). Thehaplolepideousperistomeisbelievedtobederivedfrom
thediplolepideousperistomewith oppositeexostomeandendostomeasdepicted in Fig. 10,andthat
itishomologouswithendostomalsegments.Scalebaris40pm.
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