Peristome Variations in the Genus Fissidens: an SEM Study Author(S): Bruce H

Peristome Variations in the Genus Fissidens: An SEM Study Author(s): Bruce H. Allen Source: The Bryologist, Vol. 83, No. 3 (Autumn, 1980), pp. 314-327 Published by: American Bryological and Lichenological Society Stable URL: http://www.jstor.org/stable/3242441 Accessed: 09/08/2010 07:49

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http://www.jstor.org The Bryologist 83(3), 1980, pp. 314-327 Copyright @ 1980 by the American Bryological and Lichenological Society, Inc.

Peristome Variations in the Genus Fissidens: An SEM Study

BRUCEH. ALLEN Departmentof Biology, Buckhout Laboratory,The PennsylvaniaState University, University Park, PA 16802

Abstract. Peristomes of 19 species representing two subgenera of the genus Fissidens were examined using scanning electron microscopy. Seven types of peristomes were distinguished on the basis of variations in the trabeculae and the lamellae of the dorsal and ventral surfaces. These seven types are designated the scariosus-, bryoides-, excurrentinervis-, obtusifolius-, taxifolius-, subbasilaris- and manateensis-types of peristomes. In some instances, species having similar peristome types are gametophytically similar; in other instances species having the same peristome type have different gametophytes. In still other instances, species with dissimilar peristome types have similar gametophytes.

The genus Fissidens is a homogeneous group of mosses distinguished by an unusual leaf structure. The leaves are equitant and each is composed of a ventral, boat-shaped proximal portion consisting of two vaginant laminae and an undivided distal ventral lamina; dorsally there is an undivided dorsal lamina. In addition, the leaves are distichous and complanate. In the Musci, the peristome is considered an important indicator of natural relationships (Philibert 1884-in Taylor 1962, Dixon 1932, Buck & Crum 1978). The peristome of Fis- sidens, usually described as dicranoid, consists of a single row of 16 peristome teeth that are haplolepideous (having a single row of dorsal "scales"). Thus, the genus Fissidens is a taxon apparently closely related to the Dicranaceae on the basis of the sporophyte but which possesses a distinctive gametophyte easily separating it from all other haplolepideous mosses. Conspectus of the genus Fissidens. The genus Fissidens was established by Hedwig (1801) to accommodate 14 species. Since that time the number of species ascribed to Fissidens has increased to approximately 876 (Wijk et al. 1962, 1969). Along with this increase in the number of species, a large number of subgeneric taxa has been described. Brotherus (1924) recognized 4 subgenera, viz., Polypodiopsis (C. M0ll.) Broth., Eufissi- dens Hedw. (=Fissidens), Pachyfissidens (C. M011.) Kindb. and Octodiceras (Brid.) Broth. Subgenus Fissidens was further divided into twelve sections, viz., Weberiopsis C. Mill., Reticularia Broth., Bryoidium C. Miill., Pachylomidium C. Mill., Pycnothallia C. Miill., Heterocaulon C. Miill., Semilimbidium C. MWll., Aloma C. Miill., Crenularia C. Mill., Crispidium C. Miill., Amblythallia C. Miill. and Serridium (C. Mill.). In the past, subgeneric taxa within Fissidens have been based principally on gametophytic characters. The peristome was never utilized in the interpretation of relationships within Fissidens. This is because differences seen in structure of the peristome with the light microscope appear minor. However, Florschiitz (1964) believed the current division of the genus was "highly artificial." Species he considered closely related were positioned into disparate sections. Furthermore, there has been disagreement among authors as to the number and rank of the subgeneric taxa within Fissidens, even though all treatments 007-2745/80/314-327$1.65/0 1980] ALLEN: PERISTOMEVARIATIONS 315

have utilized the same characters. Indeed, recent treatments of groups within the genus (Norkett 1969, Bruggeman-Nannenga 1978) have resulted in a reduction in the number of subgeneric taxa on the basis that variation of characters within the gametophyte may be environmentally induced. It would appear that a better understanding of relationships within Fissidens could be achieved if additional characters were utilized. The sporophyte should be considered a possible source of new characters in view of its conservative nature (Buck & Crum 1978) and the potential of recent techniques developed for observing sporophytic features, e.g., transmission electron microscopy, scanning electron microscopy (SEM), and chemical analysis (Mueller 1973). To date only three studies have been done on Fissidens using SEM: one by Berlin et al. (1974) who studied the leaf structure of nine species of Fissidens, and two by Mueller (1973, 1974) who observed the morphology of the peristome of F. limbatus Sull. and F. osmundoides Hedw. MATERIALS AND METHODS Peristomesof 22 specimensbelonging to 19 species in two subgeneraand nine sections of Fissidens (see Brotherus 1924)were used. With the exception of three species, F. manateensis, F. scariosus and F. polypodioides,peristomes viewed were taken from single populations.An attemptwas made to view the peristomesof at least six plants per gathering.Except where otherwise stated, all specimens are deposited at PAC. Specimens examined: SUBGENUSFISSIDENS. Sect. Aloma C. Muill.: F. exilis Hedw., U.S.A., Pennsylvania, Centre Co., Allen 956; F. prionodes Mont., Mexico, Chiapas, Sharp et al. 4096; F. subulatus Mitt., Brazil, Rond6nia, Reese 13332. Sect. Amblyothallia C. Miill.: F. asplenioides Hedw., Mexico, Mexico, Delagadillo 2718; Sect. Bryoidium C. Miill.: F. bryoides Hedw. sensu lato, U.S.A., Pennsylvania,Fayette Co., Allen 270; Sect. CrenulariaC. Miill.: F. radicans Mont., U.S.A., Florida, Dade Co., Pursell 2915; Sect. Heterocaulon C. Miill.: F. excurrentinervis R. S. Williams, Peru, La Libertad, Hegewald 5112; F. milobakeri L. Koch, U.S.A., California, San Mateo Co., Koch 3394 (isotype);Sect. SemilimbidiumC. Mill.: F. obtusifoliusWils., U.S.A., Kansas, DouglasCo., Cridland 250; Sect. Serridium C. Miill.: F. adianthoides Hedw., U.S.A., Pennsylvania, Centre Co., Allen 364; F. bushii (Card. & Ther.) Card. & Ther., Canada, Quebec, Fabius 2207 (DUKE);F. cristatus Wils. ex Mitt., U.S.A., Tennessee, Greene Co., Sharp4528; F. osmundoidesHedw., U.S.A., Wisconsin, Douglas Co., Schroeder M183; F. polypodioides Hedw., U.S.A., Florida, Leon Co., Pursell 634, Mexico, Chiapas, Smith et al. 2873; F. subbasilaris Hedw., U.S.A., Tennessee, Greene Co., Sharp 4514; F. taxifolius Hedw., U.S.A., Pennsylvania, Centre Co., Allen 217; Sect. Weberiopsis C. Miill.: F. gladiolus Mitt., Tanzania, Morogoro, Crosby et al. 8749 (MO); F. scariosus Mitt., Brazil, Sio Paulo, Yano 211, Minas Geraes, Frahm 1543. SUBGENUSOCTODICERAS (BRID.) BROTH.F. manateensis Grout, U.S.A., Florida, WakullaCo., Redfearn2060, Louisiana, Lafayette Parish, Reese et al. 6410. In the selection of peristomes, an attemptwas made to use maturecapsules with intact opercula. Surface features of the teeth are easily eroded once the operculumis lost from a capsule. Mature sporophyteswere dissected and mountedwith double-stickadhesive tape onto aluminumspecimen mounts. In order to avoid a buildupof electrical charge on the specimens, a thin layer of gold was applied to the specimens using a HummerII sputterer.The specimens were viewed with a Super Mini-SEMat 25 kV. RESULTS Study reveals considerable variation in the surface features of the peristomes of Fis- sidens species. Among the representatives of 19 species studied, seven types of peristome can be distinguished on the basis of variation in the trabeculae and lamellae of the outer and inner surfaces of the teeth (see Table 1). These seven types are here designated as the scariosus-, bryoides-, excurrentinervis-, obtusifolius-, taxifolius-, subbasilaris- and manateensis-types of peristomes. Scariosus-type of peristome (Fig. 1-10). The scariosus-type of peristome is exhibited by F. scariosus, (Fig. 1-2), F. radicans (Fig. 3-4), F. prionodes (Fig. 5, 10), F. exilis (Fig. 6-7), and F. subulatus (Fig. 8-9). It is characterized by a dorsal surface on which the w

TABLE1. A comparisonof the seven peristome-typesobserved in this study. Trabeculae Lamellae Outer surface Inner surface Outer surface Inner surface fimbriate smooth Smooth or papillose ON Scariosus-type Unthickened, Usually bearing High, closely o\ smooth, Il.r.- projections,l.r.-5:1 spaced horizontal 10:1 ridges Bryoides-type Unthickened, Usually bearingcolumnar Low, papillose horizontal Smooth or papillose papillose, I.r.- papillaealong the sides, ridges 10:1 1.r.-5:1 Excurrentinervis-type Unthickened, Smooth, unthickened, Smooth below, obliquely Smooth below bifurcation, smooth, low, low, 1.r.-5:1 ridgeddistally obliquelyridged 1.r.-4:1 distally Smooth Smooth below bifurcation, Or Obtusifolius-type Thickened, smooth, Smooth, thickened, 1.r.- 0 1.r.-20:1 5:1 papillose distally 0cn Taxifolius-type Unthickened, Usually papillose, 1.r.- Closely spaced, vertical, Low vertical papillose smooth, l.r.-8:1 4:1 sinuous ridges, usually ridges to papillose papillose below ,< Subbasilaris-type Thickened, smooth, Smooth, unthickened, Low, thickened, Papillose 1.r.-12:1 1.r.-5:1 horizontalsinuous 0 ridges, smooth Manateensis-type Unthickened, Smooth, unthickened, Low vertical ridges, Smooth below smooth, l.r.-3- l.r.-5:1 smooth at base, bifurcation,obliquely 4:1 papillose distally ridgeddistally 1 1.r. (lamellaeratio) is the ratio of length to width of the lamellae and is inversely proportionalto the distance between trabeculae.The higher the ratio, the closer the trabeculae. CD 00w 1980] ALLEN: PERISTOMEVARIATIONS 317

trabeculae are unthickened below the bifid area. The lamellae have numerous smooth, horizontal ridges, which run the width of the teeth (Fig. 1-2, 4-5, 7-8). These ridges cover the lamellae and vary from '/2 to 2/3 the height of the trabeculae. At and just above the tooth bifurcation, the trabeculae become thickened and the ridges on the lamellae are oriented vertically (Fig. 1, 4). Although the dorsal surfaces of the teeth of these five species are similar, the ventral surfaces are markedly different. Two variations of the scariosus- type can be recognized on the basis of the ventral trabeculae. In F. scariosus (Fig. 2), F. exilis (Fig. 6), F. subulatus (Fig. 9) and F. prionodes (Fig. 10), the ventral trabeculae appear fimbriate, with long, finger-like projections occurring along the outer edges. In F. scariosus, F. subulatus, and F. prionodes, these fimbriate projections are prominently displayed on all of the trabeculae below the bifurcation. However, they are restricted in F. exilis to the two or three trabeculae immediately below the bifurcation, with the re- maining trabeculae bearing large and, in some cases, branched papillae along the sides (Fig. 6). The trabeculae are smooth in F. radicans (Fig. 3). Because of the small sample size used in this study it is not certain that the variation exhibited in F. radicans is typical. Further studies are needed to determine the range of variability, if any, in the ventral trabeculae of F. radicans. Bryoides-type of peristome (Fig. 11-13, 16-17, 20). The bryoides-type of peristome is seen in F. bryoides (Fig. 17, 20), F. milobakeri (Fig. 11-12), and F. gladiolus (Fig. 13, 16). Characteristic of this type of peristome is the presence of numerous papillae on the trabeculae and the lamellae of the dorsal surface (Fig. 12-13, 16-17). The lamellar papillae occur on low, horizontal ridges, which are suggestive of the horizontal ridges found on the dorsal surface of the scariosus-type of peristome. As in the scariosus-type, the bryoides-type of peristome can be divided into two variations based on differences in the ventral trabeculae. In F. bryoides (Fig. 20) and F. gladiolus (Fig. 16), columnar papillae

FIGURES1-8. Peristomes of Fissidens spp. - 1. F. scariosus Mitt., dorsal surface, x700. - 2. F. scariosus Mitt., dorsal surface and ventral trabecula, x700. - 3-4. F. radicans Mont., ventral and dorsal surfaces, x700 and x 1000, respectively. - 5. F. prionodes Mont. dorsal surface, x700. - 6-7. F. exilis Hedw., side view and dorsal surface, x 100. - 8. F. subulatus Mitt., dorsal surface, x700. FIGURES 9-16. Peristomes of Fissidens spp. - 9. F. subulatus Mitt., ventral surface, x700. - 10. F. prionodes Mont., ventral surface, x700. - 11-12. F. milobakeri L. Koch, ventral and dorsal surfaces, x700. - 13. F. gladiolus Mitt., dorsal surface, x1000. - 14-15. F. obtusifolius Wils., dorsal and ventral surfaces, x1000 and x700, respectively. - 16. F. gladiolus Mitt., side view and dorsal surface, x1000. FIGURES17-23. Peristomes of Fissidens spp. - 17. F. bryoides Hedw., dorsal surface, x700. - 18-19. F. subbasilaris Hedw., dorsal and ventral surfaces, x700 and x400, respectively. - 20. F. bryoides Hedw., ventral surface, x 1000. - 21-22. F. excurrentinervis Williams, dorsal and ventral surfaces, x700 and x400, respectively. - 23. F. cristatus Wils. ex Mitt., dorsal surface at the bifurcation, x 700. FIGURES24-30. Peristomes of Fissidens spp. - 24. F. taxifolius Hedw., dorsal surface, x400. - 25. F. bushii (Card. & Ther.) Card. & Ther., dorsal surface at bifurcation, x700. - 26. F. adianthoides Hedw., dorsal surface, x400. - 27. F. taxifolius Hedw., ventral surface, x400. - 28. F. bushii (Card. & Ther.) Card. & Ther., ventral surface, x400. - 29. F. adianthoides Hedw., ventral surface at the bifurcation, x400. - 30. F. cristatus Wils. ex Mitt., ventral surface, x700. FIGURES31-38. Peristomes of Fissidens spp. - 31. F. asplenioides Hedw., dorsal surface at the bifurcation, x400. - 32. F. polypodioides Hedw., dorsal surface at the bifurcation, x700. - 33. F. osmundoides Hedw., dorsal surface at the bifurcation, x 700. - 34. F. asplenioides Hedw., ventral surface, x400. - 35. F. polypodioides Hedw., ventral surface, x400. - 36. F. osmundoides Hedw., ventral surface, x400. - 37-38. F. manateensis Grout, ventral and dorsal surfaces, x400 and x700, respectively. 318 THEBRYOLOGIST [Volume 83

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(instead of the fimbriateprojections that occur in the scariosus-type)occur along the sides of the trabeculae.In F. milobakeri(Fig. 11) the trabeculaeare smooth. The occurrenceof large papillae on the ventral surface of the peristome teeth in some species of Fissidens has been previously noted (Dixon 1922,Brotherus 1924, Grout 1943). The distinction, however, between large, columnarpapillae on the sides of the trabeculae and finger-likeprojections occurring along the outeredges of the ventraltrabeculae appears to have been overlooked. Fimbriateprojections on the marginsof ventral trabeculaeare here consideredrestricted to the scariosus-typeof peristome. Columnarpapillae ("highly cristate trabeculae,"fide Dixon 1922)are associated with the bryoides-typeof peristome. A study of the variationin peristome of the F. bryoides complex is now underway. Excurrentinervis-typeof peristome(Fig. 21-22). The excurrentinervis-typeof peristome, characteristicof F. excurrentinervis(Fig. 21-22), is of interest because of the similarity between the dorsal and ventral surfaces. The low, widely spaced trabeculaeand smooth lamellae are features common to both surfaces. In addition, the distal lamellae on both surfacespossess prominentridges that are obliquelyarranged. The presence of a prominent median line (Fig. 22) is, however, a distinguishingfeature of the ventral surface. Obtusifolius-typeof peristome(Fig. 14-15). The obtusifolius-typeof peristome is found in F. obtusifolius. This type of peristome is characterizedby smooth, greatly thickened and closely spaced dorsal trabeculae,which obscure the lamellae(Fig. 14). Ventrally(Fig. 15), the smooth, widely spaced, thickened trabeculaebelow the bifid area, and the large papillae on thick, vertical ridges on the lamellae above the bifurcationare distinctive. Taxifolius-typeof peristome(Fig. 23-36). The taxifolius-typeof peristomeoccurs in six representativesof section Serridium,i.e., F. taxifolius(Fig. 24, 27), F. cristatus (Fig. 23, 30), F. bushii (Fig. 25, 28), F. adianthoides (Fig. 26, 29), F. polypodioides (Fig. 32, 35), and F. osmundoides (Fig. 33, 36) and one representativeof section Amblyothallia,F. asplenioides (Fig. 31, 34). This type of peristome is best recognized by the presence, on the dorsal surface of the lamellae, of numerous, closely spaced, sinuose, vertical ridges, which may or may not bear papillae (Fig. 23-26, 31-33). Widely spaced vertical ridges on the lamellae and a well-developedmedian line are distinctive on the ventral surface (Fig. 27-30, 34-36). The taxifolius-typeof peristomecan be subdivided(as a category)into two groups distinguishedby the appearanceof the dorsal lamellae. In F. taxifolius (Fig. 24), F. bushii (Fig. 25), F. cristatus (Fig. 23) and F. adianthoides (Fig. 26), the sinuose vertical ridges below the bifid area are united at several points, forming horizontal lines. This combinationof vertical ridges and horizontallines gives the lamellae a reticulate appear- ance. In F. asplenioides (Fig. 31), F. polypodioides (Fig. 32) and F. osmundoides (Fig. 33), the vertical ridges lack distinct horizontallines. Subbasilaris-typeof peristome(Fig. 18-19). The subbasilaris-typeof peristome is characteristic of F. subbasilaris (Fig. 18-19). This type of peristome is best distinguishedby charactersof its dorsal surface (Fig. 18). The trabeculaeare closely spaced (often closer than shown in Fig. 18), smooth and thickened, and the lamellae consist of low, thick, sinuous ridges arrangedhorizontally below the bifid area. Above the bifurcation, these sinuous ridges become more or less vertically arranged. Manateensis-typeof peristome(Fig. 37-38). The manateensis-typeof peristome is ex- hibitedby F. manateensis (Fig. 37-38). On the dorsal surface(Fig. 38), the trabeculaeare thin and widely spaced both above and below the bifurcation.However, the lamellae are the distinctive feature of the dorsal surface. At the base of each tooth the lamellae consist of faint, vertical ridges. At approximatelyhalf the distance to the bifurcation,the vertical ridges become sharpin outline and begin to bear papillae.As the bifidarea is approached, these papillaebecome numerousand may in some cases obscure the ridges. The lamellae 324 THE BRYOLOGIST [Volume 83 are smooth below the bifurcation,but bear distinctiveoblique ridges above the bifurcation on the ventral surface (Fig. 37).

DISCUSSION AND CONCLUSIONS The infragenerictaxa of Fissidens presently recognized are based primarilyon gametophytic characters(see Miiller 1901, Brotherus 1924, Grout 1943, Gangulee 1971). Most attempts at revising the infragenericclassification of the genus have been at the sectional level in subgenus Fissidens (Potier de la Varde 1929, Grout 1936, Norkett 1969, Brugge- man-Nannenga1978), the largest and most variable of the subgenera. However, Flor- schiitz (1964)has rejected this classificationas artificial. Sporophytic characters have received little consideration in the circumscriptionof subgenerictaxa of Fissidens. Yet, preliminaryresults of the present researchindicate that the sporophyte, especially the fine surface features of the peristome, may prove to be importantin the classificationof Fissidens. In some instances, these results do not support recognitionof certain currentlyrecognized infragenerictaxa, whereas other taxa are supported. Study of some of the species examined, e.g., F. bryoides, F. exilis, F. gladiolus, F. milobakeri, F. prionodes, F. radicans, F. scariosus and F. subulatus, indicates that species with great differences gametophytically(see Table 2) can have similar peristomes. For example, for the five species possessing the scariosus-type of peristome, the limbidia, costae and laminalcells all have differentcharacter states (see Table 2). Fissidens bryoides and F. milobakeri have been relegated to section Bryoidium and section Heterocaulon, respectively. However, in both species, the gametophytesare lim- bate and have smooth cells. Both also exhibit the bryoides-typeof peristome. The dimor- phism in gametophoresof F. milobakeri is the only basis for distinguishingthese two species sectionly. Norkett (1969)is of the opinionthat section Heterocaulon is ill-founded and should be recognized only at subsectionalrank. The presence, in F. excurrentinervis (also a species of section Heterocaulon), of an altogetherdifferent type of peristome(the excurrentinervis-type)indicates that using the presence of dimorphicgametophores to distinguisha section or a subsection is untenable. Fissidens gladiolus, a species from Africa, and F. scariosus, a South American species, have been referredto section Weberiopsis.A second South Americanspecies, F. subulatus, althoughplaced in section Aloma by Brotherus(1924), resembles F. gladiolus on the basis of the gametophyte(Pursell & Reese 1980a,b).Fissidens subulatus and F. scariosus share a similartype of peristome with F. prionodes and F. exilis of section Aloma and with F. radicans in section Crenularia; whereas, on the same basis, F. gladiolus is more closely related to F. bryoides and F. milobakeri. Bruggeman-Nannenga(1978) proposed that sections Bryoidium and Aloma, distinguished primarilyby the presence or absence of limbidia,respectively, should be united. The basis for this view is the extreme variabilityin the expression of the limbidiumin Fissidens (see Crum 1964, 1973; Norkett 1969; Pursell 1976). It would appear that the gametophyticbases for maintainingBryoidium and Aloma as separate sections are mini- mal. However, the occurrence of the scariosus-type of peristome in three members of section Aloma and the occurrenceof the bryoides-typeof peristomein F. bryoidesindicate that unitingthese two sections is not justified at the present time. Another species in which gametophytecharacters are not correlatedwith sporophytic characters is F. obtusifolius. Although placed in section Semilimbidiumby Brotherus (1924)and Grout(1943), the presence of smooth cells and a narrowlimbidium on the dorsal lamina of var. kansanus, plus a close resemblance to F. exiguus (considered to be a 1980] ALLEN: PERISTOME VARIATIONS 325

TABLE2. Differencesbetween gametophytesof the 19 species of Fissidens used in this study. Plant size Limbi- Cell Cell (mm) diumI surface2 shape3 Costae4 Sect. Heterocaulon F. excurrentinervis 1-2 2 1 2 (fertile stems) 1 (sterile stems) 3 F. milobakeri 3-4 1 1 5 2 Sect. Bryoidium F. bryoides 2-7 1 1 2 2 Sect. Weberiopsis F. gladiolus 2-3 2 1 6 1 F. scariosus 3 1 1 6 4 Sect. Aloma F. exilis 1-2 2 1 2 2 F. prionodes 5 2 1 1 to 2 1 F. subulatus 3 2 1 4 to 5 1 Sect. Crenularia F. radicans 2-10 2 2 2 3 Sect. Semilimbidium F. obtusifolius 2-10 1 1 2 to 3 3 Sect. Amblyothallia F. asplenioides 10-50 2 2 2 3 Sect. Serridium F. bushii 4-7 2 3 2 to 3 2 F. taxifolius 4-20 2 2 2 to 3 1 F. cristatus 10-25 2 2 3 3 F. adianthoides 10-35 2 1 2 3 F. osmundoides 5-12 2 2 2 3 F. polypodioides 20-50 2 1 2 2 F. subbasilaris 5-10 2 2 2 to 3 3 SUBGENUSOCTODICERAS F. manateensis 50-150 2 1 2 to 4 3 = 1 Limbidium: 1 present, 2 = absent. 2 Cell surface: 1 = smooth, 2 = mammillose, 3 = pluripapillose. 3 Cell shape: 1 = rhomboid, 2 = hexagonal, 3 = rounded, 4 = quadrate, 5 = rectangular, 6 = pro- senchymatous. 4 Costa: 1 = excurrent,2 = percurrent,3 = ends below the apex, 4 = ends at midleaf.

variant of F. bryoides by Crum 1964, 1973; Pursell 1976) suggest a relationship to section Bryoidium. However, on the basis of its peristome (obtusifolius-type), which bears little resemblance to that of the bryoides-type of peristome, a close relationship seems doubtful. Six species-F. adianthoides, F. bushii, F. cristatus, F. osmundoides, F. polypodioides and F. taxifolius-assigned to section Serridium, have peristomes of the taxifolius-type. In these cases, the correlation of similar peristomes with similar gametophytes (see Table 2) is a strong indication of one natural basis for this section. While a number of species placed in section Serridium appear similar in gametophytes and in sporophytes, some species are not. A case in point is F. subbasilaris. Although 326 THE BRYOLOGIST [Volume 83 this speciesshares a numberof gametophyticcharacters with other species placed in the section:elimbate and serrate leaves, mammillose laminal cells andlateral sporophytes, F. subbasilarishas a peristomedistinct from the othersexamined. Moreover, the reported chromosome number, n = 8 (Chopra 1960, 1961), represents the lowest number and (prob- ably a different base number) reported for the section. These two features indicate that F. subbasilaris, despite similaritiesin gametophytes, is not closely related to other species of section Serridium. Fissidens asplenioides is generally placed in section Amblyothallia, characterizedby blunt, elimbate, ligulate leaves with apices curled when dry; roundish, more or less opaque laminalcells; and geniculate costae (Miiller 1901). Norkett (1969) considered Amblyothallia unworthyof recognitionand suggested that species assigned to it be transferredeither to sectionCrispidium (if axillaryglands-groups of hyalinecells-are present)or to section Serridium (if axillary glands are absent). Fissidens asplenioides lacks axillary glands and on this basis should be placed in Serridium, a conclusion supported by its taxifolius-type of peristome. By placing undue emphasis on gametophytic characters (the "circinnate" inrolled leaf tips and distinctive laminal cells), Florschiitz (1964) considered F. asplenioides and F. radicans very closely related. He thought F. radicans was possibly a variety of F. asplenioides. However, the presence of a scariosus-type of peristome in F. radicans and of a taxifolius-type of peristome in F. asplenioides does not support this view. The taxon Octodiceras has been recognized at different ranks. Originally described as a genus (Bridel 1806), it was recognized by Brotherus (1901, 1924) as a subgenus, while Mitten (1869) and Grout (1936, 1943) recognized it at the sectional level. In a recent treatment of the family in Britain and Ireland, Smith (1978) maintains it as a genus. Only one representative of this taxon has been examined, F. manateensis. Its peristome, the manateensis-type, is distinct from all others observed in this study. However, before any generalizations concerning the ranking of Octodiceras can be made, peristomes of other members of the subgenus will have to be examined. In conclusion, SEM studies of the genus Fissidens show a wide variation in the surface features of the peristome. However, just how wide this variation is will be determined only with the examination of additional species. Species having the scariosus- and bryoides-types of peristomes show no consistent gametophytic features, those species exhibiting the taxifolius-type of peristome do show more or less uniform gametophytic character states. That the gametophytes and sporophytes in mosses have evolved some- what independently has long been recognized (Philibert 1884--in Taylor 1962, Dixon 1932, Steere 1947). The results of this study certainly corroborate this. Furthermore, these studies indicate that peristome types may be important in consid- ering natural relationships within Fissidens. However, exactly how useful peristome-types will be in a natural classification of Fissidens can not be determined on the basis of the small number of peristomes considered in this study, which included only one representative of each of the sections Bryoidium, Crenularia, Semilimbidium, Amblyothallia and Octodiceras, and omitted several other sections. In addition, because, in most cases, only one population from each species was examined, the range of variation in these peristome- types has not been determined. Further discussion of a natural classification of Fissidens utilizing peristome types must await broader sampling of both populations and species. This paperis based on a portionof a thesis submittedto the GraduateSchool of The Pennsylvania State University in partialfulfillment of the requirementsfor the degree of Masterof Science, 1980. I thank Dr. R. A. Pursell for his advice, generous investment of time throughoutthis investigation, and critical help with the manuscript.Contribution No. 191 from the Departmentof Biology, The 1980] ALLEN: PERISTOMEVARIATIONS 327

Pennsylvania State University. The loan of specimens from herbaria cited in the text is also gratefully acknowledged.

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