Peristome Development in Mosses in Relation to Systematics and Evolution. IV. Haplolepideae: Ditrichaceae and Dicranaceae Author(S): Jonathan Shaw, Brent D

Peristome Development in Mosses in Relation to Systematics and Evolution. IV. Haplolepideae: Ditrichaceae and Dicranaceae Author(s): Jonathan Shaw, Brent D. Mishler, Lewis E. Anderson Source: The Bryologist, Vol. 92, No. 3 (Autumn, 1989), pp. 314-325 Published by: American Bryological and Lichenological Society Stable URL: http://www.jstor.org/stable/3243400 Accessed: 17/11/2010 10:38

Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use.

Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=abls.

Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected].

American Bryological and Lichenological Society is collaborating with JSTOR to digitize, preserve and extend access to The Bryologist.

http://www.jstor.org The Bryologist 92(3), 1989, pp. 314-325 Copyright ? 1989 by the American Bryological and Lichenological Society, Inc.

Peristome Development in Mosses in Relation to Systematics and Evolution. IV. Haplolepideae: Ditrichaceae and Dicranaceae

JONATHANSHAW Departmentof Biology, Ithaca College,Ithaca, NY 14850

BRENTD. MISHLERAND LEWISE. ANDERSON Departmentof Botany, Duke University, Durham, NC 27706

Abstract. The classificationof mosses into subclassesand ordersis based to a large extent on the morphologyof the peristome teeth, yet little informationexists on developmentof peristomes. In thispaper we describethe sequencesof cell divisionsleading to peristomeformation in six species of mosses representingtwo families with haplolepideousperistome structure. The earliestdevelop- mental stages conformto the pattern documentedin other mosses and highlightthe uniformityof these early stages among mosses of diverserelationship. Peristome development in haplolepideous mosses divergesfrom the patternfound in diplolepideousspecies when each of eight cells in the Inner PeristomialLayer undergoesanticlinal divisions.Haplolepideous species share a pattern of peristome developmentthat appears to be unique to this group of mosses. Similarities in the arrangementof cells comprisingmature haplolepideousperistomes and early stages of Bryum-type diplolepideousperistomes may indicatea relationshipbetween these peristome types, or may be due in part to evolutionaryconvergence. Developmental evidence suggests that haplolepideousperistome teeth are homologousto the cilia of Bryum-typeperistomes rather than to the endostomesegments, as is commonly thought.

Philibert (1884-1902) described the seemingly there is a vertical zigzag line through the center of endless variation in peristome morphology found each tooth. Thus, Philibert called the first type hap- in mosses and was able to organize the variation he lolepideous in reference to the single column of wall observed into just a few basic types of peristomes. remnants on the outer surface of each tooth, whereas Subsequently, Fleischer (1902-1923) utilized Phi- in the diplolepideous type there are two side by side libert's morphological information and revised the columns on the outer surface. ordinal and familial classification of mosses so that With only one known exception [Mittenia plu- the major taxonomic groups reflected similarities in mula (Mitt.) Lindb.-Shaw 1985; Stone 1961], ar- peristome structure. Fleischer's system, with some throdontous peristomes are formed from periclinal relatively minor adjustments, is still in use today. wall pairs in the three innermost cell layers of the Peristomes can be divided into nematodontous amphithecium of moss capsules. These layers, types, in which the teeth are made of whole elon- named by Blomquist and Robertson (1941) in their gated cells with uniformly thickened walls, and ar- classic paper on peristome development in Aula- throdontous types in which the teeth consist of rem- comnium heterostichum, are the Inner, Primary, and nants of cell walls only (Mitten 1859; Philibert 1884- Outer Peristomial Layers (IPL, PPL, and OPL, re- 1902). Peristomes in the Tetraphidaceae and the spectively, from the inside outward). Polytrichaceae represent two contrasting types of Edwards (1979, 1984) investigated the number of nematodontous peristomes which may have little cells comprising the three peristomial layers in a to do with one another evolutionarily (Shaw & An- wide variety of mosses and proposed a convention, derson 1988). which he called the peristomial formula, to make Philibert (1884b) distinguished two kinds of peri- comparisons among taxa simpler. The peristomial stomes within the general arthrodontous type: Hap- formula lists the typical number of cells in each of lolepideous and diplolepideous. Haplolepideous the peristomial layers in one-eighth of the capsule's peristomes generally consist of a single ring of 16 circumference. The number of cells in the OPL and teeth, each tooth having horizontal lines across the PPL is relatively uniform throughout arthrodontous outer face, but without vertical lines on the outer mosses and most variation among taxa occurs in surface. Diplolepideous peristome teeth also have the number of cells in the innermost layer, the IPL. horizontal lines on the outer surface; in addition The formulae for diplolepideous peristomes vary 0007-2745/89/314-325$1.35/0 1989] SHAW ET AL.: PERISTOMEDEVELOPMENT IN HAPLOLEPIDEAE 315

between 4:2:2 and 4:2:14. That is, there are gener- Dicranum scopariumwas collected on several occasions ally 32 OPL cells, 16 PPL cells, and 16 to 112 IPL from a rockyslope alongthe Eno River at U.S. 70, Orange and New cells in the circumference of the Co., NC (Mishler3757) along Hope Creek in capsule. Duke Forest,Orange Co., NC (Mishler3759). Collections In contrast to the high degree of variation in the of D. condensatumwere made at: CampbellLake, Ches- number of IPL cells found among diplolepideous terfield Co., SC (Mishler 3746); Sandhills Game Lands, peristomes, Edwards (1979, 1984) found very little ScotlandCo., NC (Mishler3747); and White Lake,Bladen NC variation among haplolepideous peristomes. In fact, Co., (Anderson25167). Dicranumrhabdocarpum was collectedin the San JuanMts., San Juan CO Edwards that Co., (Newton, suggested haplolepideous peristomes 1988). Voucher specimens are deposited in DUKE. almost uniformly exhibit a 4:2:3 peristomial for- Plants were maintainedin the Duke University green- mula. Moreover, Edwards pointed out that in hap- houses and sporophytesat various developmentalstages lolepideous peristomes, every third anticlinal wall were sampledperiodically. Sporophytes were fixed in for- embeddedin and sectioned in the IPL is with an anticlinal wall in the malin-acetic-alcohol, paraffin, aligned on a rotarymicrotome accordingto standardtechniques PPL, whereas the intervening IPL walls are not (Johansen 1940). Swollen, almost mature capsules were aligned with PPL or OPL walls. In diplolepideous cut with a razorblade in order to facilitatecomplete in- peristomes, either all anticlinal IPL walls are aligned filtrationof the fixative. For additional details regarding our methods of and see with those in the PPL and OPL (Funaria type; Ed- fixation, embedding, sectioning, Shaw et al. (1987). wards 1984) or none is aligned (Bryum type; Ed- wards 1984). On the basis of these observations, Edwards (1984) and others (e.g., Vitt 1984) have RESULTS argued that mosses which share a haplolepideous peristome structure constitute a monophyletic group. As in our previous studies, we emphasize trans- This paper is fourth in a series of contributions verse sections because most of the distinguishing describing development of the peristome teeth in features of the different peristome types concern the in mosses in relation to systematics and evolution number and arrangement of cells the three con- (Shaw & Anderson 1988; Shaw et al. 1987, 1989). centric peristome-forming layers. We have exam- An extensive review of the literature on peristome ined many longitudinal sections and have not ob- morphology and development was provided in the served systematically significant variation among In we second of these (Shaw et al. 1987). In the present species. our previous studies, have docu- in paper we describe the sequences of cell divisions in mented each developmental stage great detail. In we the immature sporophytes preceding deposition of the the present paper delete some of photograph- peristome teeth in six species with haplolepideous ic documentation for the sake of brevity; enough peristomes. Specifically, we sought to answer the documentation is provided to show that the earliest following questions: 1) Do the earliest develop- developmental stages are remarkably uniform. De- mental stages in these haplolepideous species con- velopment of the peristomial layers is first de- form to the pattern documented previously in dip- scribed in the two species of Ditrichum, followed lolepideous and nematodontous species? 2) At what by briefer descriptions of development in Trema- developmental stage do haplolepideous peristomes todon and the three species of Dicranum. diverge from diplolepideous peristomes of the a) Ditrichum pallidum. -As in other mosses, the Bryum and b) Funaria types? and 3) Is there a pat- sporophyte of D. pallidum grows as a result of di- tern of development (i.e., a sequence of cell divi- visions of a two-sided apical cell. However, as in sions) which is unique to and shared by species with the other mosses we have studied, the apical cell haplolepideous peristomes? ceases dividing while the embryonic sporophyte is only 2-5 mm long and is scarcely exserted beyond the perichaetial leaves. Most linear growth of the MATERIALSAND METHODS embryonic sporophyte is a result of cell elongation rather than division. While the cell is still We investigatedperistome development in six species apical representingtwo families of haplolepideousmosses: Di- active, the sporophyte apex is relatively pointed and trichumlineare (Sw.) Lindb., D. pallidum(Hedw.) Hampe spear-like and the merophytes can be plainly dis- (Ditrichaceae),Trematodon longicollis Michx., Dicranum cerned (Fig. 1). As soon as the apical cell ceases condensatumHedw., D. rhabdocarpumSull., and D. sco- dividing the apex becomes broadly rounded (Fig. parium Hedw. (Dicranaceae).Both families are in the Di- cranales. 2) and the spear-like shape is lost. Ditrichum lineare was collected from a coastal plain A section from just below the apex of a sporo- roadbank along State Highway 210, Bladen Co., NC phyte with an actively dividing apical cell shows (Mishler3758). Ditrichumpallidum was collected at in- two cells (Fig. 3). These two cells are either the two tervals from Februaryto Marchat Bennett Place, (Shaw, of 1987) and Duke UniversityGolf Course(Anderson 24682), most recently formed derivatives the apical cell, both in Durham, NC. Trematodonlongicollis originated or one is a derivative and the other is the apical cell at the Union coppermine, Rowan Co., NC (Shaw, 1986). itself. (These two alternatives cannot be distin- 316 THE BRYOLOGIST [VOL. 92

0ia 0

p Pi

(13)- 0 ____ -;a ~7 _-_ an

___ (28 (21 I -02 Is

'an Nil I15 1989] SHAWET AL.: PERISTOME DEVELOPMENT IN HAPLOLEPIDEAE 317

guished in our sections.) Each of the two derivatives In contrast, the first cell of the adjacent quadrant, next undergoes an anticlinal division resulting in between 12 and 3 o'clock in Figure 4, was periclinal four cells in transverse view, the quadrant stage (see instead of anticlinal, so that the first division of this Fig. 18, D. lineare). These four cells then undergo quadrant produced an endothecial cell to the inside a rather complex series of divisions which differ- and an amphithecial cell to the outside. This latter entiate the two fundamental embryonic layers of sequence is much less commonly observed in our the moss sporophyte: Amphithecium and endothe- studies. Regardless of the precise method of cell cium. division, the result is four inner endothecial cells Two types of division sequences leading to the surrounded by eight outer amphithecial cells (see differentiation of amphithecium and endothecium Fig. 19, D. lineare). were observed in Ditrichum pallidum. Both types Each of the eight amphithecial cells then divides are visible in Figure 4, in which more divisions have periclinally and more or less synchronously, form- occurred in the two left quadrants than in the two ing an inner ring of eight cells in transverse section on the right. Two of the original quadrant cells in (Fig. 5i), which is the inner peristomial layer (IPL). Figure 4 originated from one merophyte while the Immediately afterwards, through more or less syn- other two quadrant cells originated from the op- chronous anticlinal divisions, the outer layer be- posite merophyte. Two of the quadrants thus are comes 16-celled (Fig. 5). The four central endothe- older, which, combined with the possibility that the cial cells are still undivided. section shown may be somewhat tangential, could Development of the amphithecium continues explain the lack of synchrony in the divisions. The through an alternating series of periclinal and an- original quadrant between 9 and 12 o'clock is ticlinal divisions. More or less synchronously, cells 3-celled, the quadrant between 6 and 9 o'clock is in the outermost layer first divide periclinally, add- 5-celled, while both quadrants between 12 and 6 ing a ring of cells to the inside, then divide anti- o'clock are only 2-celled. In the quadrant between clinally, doubling the number of cells in the outside 3 and 6 o'clock the wall dividing its two somewhat layer (Fig. 5-10). The result is that each layer has unequal cells is obliquely anticlinal, extending be- twice the number of cells as the next layer inward. tween an interior and a surface wall. When formed, In Figure 5, for example, there are sixteen cells in the second wall would be periclinal, extending from the outer amphithecial layer and eight in the inner one interior wall to another and cutting off the fourth layer. The endothecium is still 4-celled. In Figure cell of the endothecium. This sequence is typical of 6, the amphithecium has become three layers thick most mosses. and some of the cells in the outer layer have divided

FIGURES1-21. Longitudinaland transversesections of young sporophytesof Ditrichum.a, air space;an, annulus; i, inner peristomiallayer (IPL); o, outer peristomiallayer (OPL);o2, OPL 2; p, primaryperistomial layer (PPL);s, spore layer; ss, spore sac; t, peristome tooth. All magnificationsare x 263, unless otherwise indicated. - 1-17. D. pallidum. - 1. Young apex of sporophytewith an actively dividing apical cell. - 2. Older sporophytein which the apical cell has ceased dividing. The capsuleregion has not yet begun to swell, x 79. - 3. Transversesection fromjust below the apex. - 4. Transversesection of a young sporophyteshowing differentiationof amphitheciumand endothecium. - 5. Transversesection showing four endothecial cells surroundedby two layers of amphithecium. - 6. Transversesection showing three amphitheciallayers surroundingthe endothecium,which has begun dividing. - 7. Transversesection showingasymmetrical anticlinal divisions beginningin the IPL. Divisions in the endotheciumhave continued.The amphitheciumconsists of three layerswith anticlinaldivisions beginningin the outermostlayer. - 8. Transverseview showingthree IPL cells adjacentto each pair of PPL cells. The amphitheciumstill consists of three layers. - 9. The amphitheciumnow consists of four to five layers;the peristomiallayers are differentiated.Anticlinal divisions are occurringin the IPL; the peristomialformula is 4:2:3-4. - 10. Transversesection showing a 5-layered amphithecium.Anticlinal divisions in the IPL have produceda 4:2:5-6 cell arrangement.- 11. Longitudinalsection of a capsuleapex that has attainedits matureform, with a slight amount of peristomialwall deposition. Note the dark sporogenoustissue in the urn. - 12. Longitudinalsection at the annularlevel showingthe spatialrelationship between the sporogenouslayer, the peristomiallayers, the outer spore sac, the air space, and the annulus.Note that the IPL is 2-layeredbelow the annulus.- 13. Longitudinalview of a nearlymature tooth (t) showingthe papilloseornamentation. - 14. Transverseview at the annularlevel showingthickened walls on cells of the PPL, OPL, and OPL2 (o2). - 15. Transverseview fromjust above the annularregion showingthe continuousperistomial membrane. - 16-17. Trans- verse sections from the middle (16) and upper (17) opercularregion showing the divisions of the peristome teeth. - 18-21. D. lineare. - 18. Transversesection of young sporophytenear apex, showing a quadrantof cells; two of the cells originatedfrom one merophyte,two from another. - 19. Laterstage showingthe beginningof differentiationof endotheciumand amphithecium.- 20. Laterstage in which the endotheciumis 4-celled, the amphitheciumconsists of two rings of cells. - 21. A third ring of cells (PPL)has been added to the amphithecium.Anticlinal divisions are beginningin the IPL. 318 THE BRYOLOGIST 92 [VOL. anticlinally. The quadrant between 12 and 3 o'clock the 4:2:3 pattern consistently appears but is often in Figure 6, for example, has six outer cells. This transitional. pattern of alternating anticlinal and periclinal di- All the cell layers present in the mature sporo- visions is characteristic of all mosses that have been phyte are formed before the capsule begins to swell studied developmentally. More detailed descrip- appreciably. After the three layers are differentiated, tions of these divisions are provided in our earlier the capsule swells and attains its mature shape be- papers (Shaw & Anderson 1988; Shaw et al. 1987, fore the peristome teeth are formed (Fig. 11). The 1989). mature capsule has a long-rostrate operculum which When the amphithecium consists of three layers, is up to two-thirds as long as the urn. The urn has cells in the innermost layer, the IPL, begin to divide a well-developed air space at maturity (Fig. 12a). (Fig. 6-8). Each of the eight IPL cells undergoes an The peristome of D. pallidum forms by deposi- asymmetrical anticlinal division resulting in a larger tion of wall material on the periclinal wall pairs of cell and a smaller cell (Fig. 6-7). Shortly thereafter, the IPL and PPL (Fig. 12i, p). The IPL extends the larger of the two derivatives undergoes another downward in the capsule urn as the outer spore sac, anticlinal division. The result is three smaller IPL while the PPL (p) reaches the air space (a). Because cells derived from each original IPL cell (Fig. 8i), of an additional periclinal division in the IPL in the although in Figure 8, a few cells have not yet di- region of the urn, the outer spore sac is two cell vided. The three derivative cells lie adjacent to two layers thick (Fig. 12ss). Below the annulus the OPL cells in the PPL (Fig. 8p). Note that every third (o) also becomes two-layered through periclinal di- anticlinal wall in the IPL is aligned with an anticlinal visions, forming the inner portion of the capsule wall in the PPL, but that the two intermediate IPL wall. At maturity, the peristome teeth bear a con- walls are not aligned. This is precisely the IPL/PPL spicuous papillose ornamentation on both the inner pattern said to be characteristic of haplolepideous and outer surfaces (Fig. 13t). At the base of the peristomes at maturity. peristome, additional cell layers external to the PPL There now ensues a remarkable period of coor- form thickenings; these are often referred to as pre- dinated differential growth as the developing cap- peristomial thickenings (Fig. 13-14). It is notewor- sule enlarges and matures. Cells in the outermost thy that both periclinal and anticlinal walls of the amphithecial layer undergo periclinal divisions so PPL, OPL, and OPL2 contribute wall material to that the amphithecium becomes four, then five lay- the peristome at this level. Above this basal level, ers thick (Fig. 9). There are now two layers of cells the peristome of D. pallidum forms a continuous outside the OPL. At this stage the three peristomial ring of thickening (Fig. 15). Further upward, this layers have differentiated and the peristomial for- basal membrane divides into narrow divisions (Fig. mula is 4:2:3, the typical haplolepideous pattern. 16-17) which extend several hundred micrometers However, cells of the PPL now undergo enlarge- into the opercular region. ment, each becoming more or less lenticular, ex- Ditrichum lineare.- We observed only early stages panding inward and outward. The cells of the IPL of peristome development in D. lineare, but they and OPL, which enlarge much less, accommodate are identical to those of D. pallidum. We have in- to the changes in the shape of the PPL. In section, cluded only a few figures of D. lineare to illustrate one IPL cell and one pair of OPL cells fit into each the similarities. Figure 18 is a quadrant stage similar V-shaped area alternating with the convexities of to all mosses that have been studied. Differentiation the enlarged cells of the PPL (Fig. 9-10). None or of amphithecium and endothecium is shown in Fig- few of the anticlinal walls of the IPL are now strictly ure 19. Early stages in the formation of the peristo- aligned radially with anticlinal walls of the PPL, mial layers are shown in Figures 20 and 21. In Fig- although alternate radial walls of the OPL are still ure 20, the IPL has formed and the number of cells aligned with those of the PPL. in the outer layer of the amphithecium has doubled Additional anticlinal divisions then occur in the through anticlinal divisions. Periclinal divisions in IPL, however, and eventually obscure the 4:2:3 pat- the outer layer then produced the PPL (Fig. 21). tern. These divisions have begun in Figure 9, in Cells of the IPL in Figure 21 are undergoing asym- some sectors of which there are four IPL cells op- metrical divisions. These two figures are compa- posite two PPL cells. In Figure 10, anticlinal divi- rable to Figures 5 and 6 of D. pallidum. sions in the IPL (i) have resulted in five or six IPL Trematodon. -The earliest developmental stages cells lying adjacent to two PPL cells; the peristomial of the peristomial region in T. longicollis are iden- formula is now 4:2:5-6. We found these additional tical to those of Ditrichum pallidum (and all other divisions in the IPL to be consistently present in all arthrodontous species we have studied). The em- sporophytes ofD. pallidum, as well as in some other bryonic sporophyte with an actively dividing apical haplolepideous species, as described below. Thus, cell is more or less pointed and the merophytes can 1989] SHAW ET AL.: PERISTOMEDEVELOPMENT IN HAPLOLEPIDEAE 319

be readily distinguished (Fig. 22). The apical cell sion occurs in each of the eight IPL cells, followed ceases dividing at a very early stage and most of the by another anticlinal division in the larger deriva- elongation of the developing sporophyte is due to tive (Fig. 34-35). At this stage the peristomial for- cell enlargement, as in other mosses. mula is 4:2:3 and every third anticlinal wall in the Early development involves differentiation of IPL is more or less aligned with an anticlinal wall amphithecium and endothecium, followed by al- in the PPL (Fig. 35). ternating periclinal and anticlinal divisions in the The same sequence of swelling of the PPL cells amphithecium (Fig. 23). When the amphithecium and repositioning of cells of the OPL and IPL occurs consists of three layers, asymmetrical anticlinal di- in D. scoparium (Fig. 35-36) as in Ditrichum and visions commence in the eight IPL cells (Fig. 24). Trematodon. Most of the previous alignment of ra- Additional anticlinal divisions in each of the larger dial walls in the IPL and PPL disappears (Fig. 36). of the two IPL derivatives results in three IPL cells In the latter figure, which is just prior to deposition lying adjacent to two PPL cells (Fig. 25), just as in of the peristome teeth, cells of the IPL undergo ad- D. pallidum (Fig. 8). However, in contrast to D. ditional divisions and the final peristomial formula pallidum, no additional divisions occur in the IPL becomes 4:2:4-6. Note also the outer layer of the of Trematodon longicollis (Fig. 26); the 4:2:3 peri- endothecium (Fig. 36s) which is continuous with stomial formula is maintained through peristome the spore layer lower in the capsule. maturation. Peristome teeth form by deposition of additional The capsule of T. longicollis is held in a more or material on all or portions of the adjoining periclinal less horizontal position (due mainly to bending of walls of the IPL and PPL (Fig. 37-39), followed by the seta just below the capsule); it is linear-cylin- eventual resorption or lysis of the surrounding wall drical with an extremely long sterile neck region and material. A single PPL cell is involved in the for- a long-rostrate operculum. A longitudinal section mation of the outer portion of each tooth, while two of a capsule in which peristome formation is just to three cells of the IPL are involved in forming the beginning shows the position of the sporogenous inner portion of each tooth. The teeth are thus two- tissue in relation to the peristomial layers. The IPL layered, each cemented together by a thin middle extends downward into the urn as a bistratose outer lamella. A longitudinal section through a capsule in spore sac (Fig. 27). The peristome teeth form from which deposition of peristome wall material is oc- periclinal wall pairs in the IPL and PPL, and also curring (Fig. 38) shows the similarity of Dicranum to some extent from transverse walls of the IPL (Fig. to Ditrichum (Fig. 12) and Trematodon (Fig. 27). 28). The latter are responsible for the prominent Deposition can be seen in adjoining walls of the IPL articulations on the inner face of each peristome and the PPL. There is no deposition in the OPL. tooth. Wall deposition is more extensive at the ex- The air space (Fig. 38a) terminates the PPL, while treme base of the peristome and involves cells in the IPL continues downward and becomes the outer the OPL, as in D. pallidum. A transverse section spore sac. from the annular region just as deposition of the A longitudinal section through a nearly mature peristomial wall material is beginning shows that operculate capsule (Fig. 39) shows the position of three IPL cells, which have broken down leaving the peristome and associated thickenings at the base, only their anticlinal walls, lie adjacent to two PPL which were discussed above. The OPL has not yet cells (Fig. 29). The mature peristomial formula is been resorbed and, near the annulus, consists of two thus 4:2:3. layers of cells. In this figure the spore sac has en- Dicranum scoparium. - The early developmental larged and now completely fills the air space. At this stages in this species are identical to those in the stage meiosis has occurred and the spores are free two previous genera. Differentiation of the amphi- within the spore sac. A transverse section slightly thecium and endothecium involves a series of above the annulus of a capsule that is about the obliquely anticlinal divisions in a quadrant of cells same age as that in Figure 39 is shown in Figure just below the sporophyte apex (Fig. 30-31). We 37. Peristome deposition is essentially complete in observed no curved periclinal divisions in the quad- both figures. rant cells like those in D. pallidum (Fig. 4), although A longitudinal section of a mature tooth (Fig. 40) such divisions occur occasionally during the differ- shows the two layers, which were separated by the entiation ofamphithecium and endothecium in oth- force of sectioning. The inner layer to the left (i) er mosses (reviewed by Shaw & Anderson 1988). A was contributed by the IPL, while the outer layer regular alternation of periclinal and anticlinal di- to the right (p) was contributed by the PPL. The visions follows in the amphithecium (Fig. 32-33). OPL has been resorbed. Approximately equal At a stage precisely comparable to that in Ditrichum amounts of wall material were contributed by the and Trematodon, an asymmetrical anticlinal divi- two peristomial layers. The thick-walled cells at the 320 THE BRYOLOGIST [VOL. 92

0 pe

a no ai :?s: -

ani 1989] SHAW ET AL.: PERISTOME DEVELOPMENT IN HAPLOLEPIDEAE 321 base of the tooth in Figure 40 apparently act as a on the outer walls of a single column of IPL cells. "hinge" or "anchor." A spore is shown at the left The thick-walled anchor cells are visible at the base above, and the thick-walled cells of the annulus at of the tooth opposite the heavily thickened annulus. the right below. A transverse section somewhat above the annulus Dicranum condensatum. -A longitudinal section of a slightly younger capsule is shown in Figure 48, (Fig. 41) of a very young sporophyte shows the early in which lysing of the cells surrounding the peri- differentiation of the capsule (above the arrow) and stome is still in progress. setae (below). The apical cell produces derivatives Dicranum rhabdocarpum.--This species differs which in turn divide in a predictable fashion (Fig. from D. scoparium and D. condensatum in having 42-43). Later stages (Fig. 44-45) show enlargement erect and symmetric capsules. Some bryologists place of the cells of the PPL and the accommodation by it in a separate genus, Orthodicranum Loeske. Peri- the OPL and IPL. Note that a second layer of cells stome development, however, is identical in all three is formed outside the OPL. species. We include three figures to document the The two-layered structure of the mature peri- similarity. Figure 49 shows formation of the IPL, stome is clearly revealed in transverse and longi- which can be compared to Figures 32 and 42, as tudinal sections of mature capsules. An enlargement well as to Figures 5 and 23 of Ditrichum and Tre- of a transverse section of a single tooth (Fig. 46) matodon. The PPL forms in the usual way (Fig. 50) shows the outer layer, to the right, which was formed followed by OPL formation and swelling of the PPL by deposition on the inner wall of a single PPL cell. (Fig. 51), accompanied by accommodation of the The inner layer of the tooth, to the left, was formed changes in shape of the latter by the IPL. Deposition from the outer walls of three cells in the IPL. The sequences are the same as shown for the other species. remainder of the walls of the two lower cells of the IPL have lysed while the top cell is still visible in DISCUSSION full outline and is only beginning to break down. Figure 47 shows a longitudinal section of a por- We can now answer the questions about devel- tion of an operculate but mature capsule in which opment of the haplolepideous peristome type which the two peristome layers were split during section- were posed in the introduction of this paper. Yes, ing. The outer layer (to the right) was deposited on the earliest developmental stages in these haplole- the inner walls of a single column of PPL cells. The pideous species do conform to the pattern docu- inner layer (to the left) was formed by deposition mented previously in diplolepideous and nemato-

FIGURES22-40. Transverseand longitudinal sections of sporophytesof Trematodonlongicollis and Dicranum scoparium.a, air space; an, annulus;i, inner peristomial layer (IPL); o, outer peristomial layer (OPL);p, primary peristomiallayer (PPL); s, spore layer;ss, spore sac; t, peristometooth. All magnificationsare x 263, unless otherwise indicated. - 22-29. T. longicollis.- 22. Longitudinalsection of a young sporophytein which the apical cell is actively dividing. The calyptrasurrounds the sporophyte.- 23. Transverseview of a young sporophytewith four endothecial cells surroundedby two layers of amphithecium.- 24. Older sporophytewith three amphitheciallayers surrounding the endotheciumin which divisions are occurring.Note asymmetricalanticlinal divisions in the IPL. - 25. Transverse section showing a 4-layeredamphithecium. The peristomialformula is 4:2:3. - 26. Nearly mature sporophytejust prior to peristome deposition. The peristomial formula is still 4:2:3, x 162. - 27. Longitudinalsection through a nearly maturecapsule showing the air space, the spore sac, and the spore layers in the urn, and the three peristomial layersin the operculum, x 16. - 28. Longitudinalsection at the annularlevel showingthe developingperistome tooth along the joint vertical walls of the IPL and the PPL and the thickened walls of the PPL and OPL adjacentto the annulus. - 29. Transversesection showinganticlinal IPL walls remainingafter the IPL cells have brokendown. The peristomialformula is 4:2:3, x 66. - 30-40. D. scoparium.- 30. Transversesection near the tip of the sporophyte, showinga quadrantof cells. - 31. Slightlylater stage showingcurved anticlinal divisions preparatoryto differentiation of amphitheciumand endothecium. - 32. Transversesection showing a 3-layeredamphithecium surrounding four endothecialcells. - 33. Periclinaldivisions in the outermostlayer have increasedthe numberof amphitheciallayers to four in part of the right side. Anticlinaldivisions have occurredin the outermostlayer. The peristomialformula is 4:2:1. - 34. Asymmetricalanticlinal divisions are occurringin the IPL. The endothecialcells are also dividing. The peristomialformula is 4:2:2, at least in part. - 35. The amphitheciumconsists of four layers;anticlinal divisions in the IPLhave produceda 4:2:3cell arrangement.- 36. Anticlinaldivisions in the IPLhave continuedand the peristomial formulais 4:2:4-6. Note the wedge-shapedIPL cells that conformto the shape of the area betweenadjacent PPL cells. - 37. Transversesection showing matureperistome teeth formed from periclinalPPL-IPL wall pairs. - 38. Longi- tudinal section of portion of capsule in which peristomedeposition has begun on the outside wall of the IPL and the inside wall of the PPL;the multilayeredspore layer and the air space are shown below the annulus. - 39. Laterstage in which peristomedeposition (t) is nearlycomplete; note below that the spore sac has enlargedto include most of the air space. - 40. Longitudinalview of a maturetooth; the respectivelayers forming the IPL and the PPL are visible due to the force of sectioning.Note the thickenedPPL and OPL cells below the tooth. 322 THE BRYOLOGIST [VOL. 92

(~41) (44 i

iii:: V ~n~

(46)? (4) (8 ____ t~ ;lp

~lir~I

FIGURES41-5 1. Longitudinaland transversesections throughsporophytes of Dicranum.i, inner peristomiallayer (IPL);o, outerperistomial layer (OPL); o2, OPL 2; op, operculum;p, primaryperistomial layer (PPL). All magnifications are x 263, unless otherwiseindicated. - 41-48. D. condensatum.- 41. Longitudinalview of a young sporophytewith an actively dividing apical cell. Arrow marks the level of the annulus. - 42. Transverseview of a young sporophyte with two amphitheciallayers surrounding four endothecialcells. - 43. Transversesection showingthree amphithecial layers surroundingfour endothecial cells. - 44. Transversesection of an older sporophytewith five amphithecial layers. The peristomialformula is 4:2:3-4. - 45. Nearly mature sporophytein which anticlinaldivisions in the IPL have produceda cell arrangementof 4:2:4-6. - 46. Transversesection of a single peristometooth, showing the two layers. The layer to the right is derived from the inner wall of the PPL; the inside layer to the left is from the outer wall of the IPL. - 47. Longitudinalsection of a maturebut operculatecapsule showing a peristometooth with thickened PPL and OPL cells below it. Note the thin-walledIPL cells on the lower left. - 48. Transverseview of a mature capsuleshowing the peristometeeth. - 49-51. D. rhabdocarpum.- 49. Transversesection of capsulewith a 2-layered amphithecium.- 50. Later stage showing beginningof a third layer in the amphithecium;the endotheciumis still 4-celled. - 51. Later stage in which the three peristomiallayers are differentiated;the cells of the PPL are enlarged and the cells of the IPL have accommodatedto the swelling.

dontous species; the early stages of peristome sequence of cell divisions involves the differentia- development are remarkably uniform in mosses of tion of amphithecium and endothecium from a very diverse relationships. In fact, development of quadrant stage, followed by alternating anticlinal the amphithecium up to the point at which three and periclinal divisions in the outermost amphithe- layers are formed is virtually identical in all the cial layer. mosses we have described to date (Shaw & Ander- There is some variation in the mode by which son 1988; Shaw et al. 1987, 1989), and this pattern the amphithecium and endothecium are differen- does not differ from the sequences published pre- tiated, but this variation can occur within one spo- viously by others (Blomquist & Robertson 1941; rophyte, as in Ditrichum pallidum (Fig. 4). Chopra Evans & Hooker 1913; Mueller 1973; Saito 1956; and Sharma (1958) also reported within-capsule Saito & Shimoze 1954; Stone 1961). The uniform variation in the pattern of cell divisions differen- 1989] SHAW ET AL.: PERISTOME DEVELOPMENT IN HAPLOLEPIDEAE 323 tiating amphithecium and endothecium in Pogo- when the larger but not the smaller derivative of natum. The most typical pattern of cell divisions each asymmetrical division in the IPL divides again. involves a series of tangential-anticlinal divisions Although Blomquist and Robertson (1941) stated (as in Fig. 31), and the variation which occurs ap- that the peristomial layers in Aulacomnium heter- pears to have little or no systematic significance (see ostichum, a diplolepideous species, pass through a further discussion in Shaw & Anderson 1988). 4:2:3 stage, their drawings show that development Even in Tetraphis pellucida, a species that is gen- conforms to the pattern we have documented in erally classified in a separate subclass of mosses be- other diplolepideous species. The 4:2:3 stage, ifdis- cause of its unique nematodontous peristome struc- cernable at all in diplolepideous species, is transient ture, the early stages of development in the and occurs only during the short time period in peristomial layers are identical to those in species which one of the two derivative IPL cells has di- with arthrodontous peristomes (Shaw & Anderson vided but the other has not. In such cases, two of 1988). The other type of nematodontous peristome, the three IPL cells (adjacent to a pair of PPL cells) which occurs in the Polytrichaceae, differs in de- are small and the third, which is just about to divide, velopment to a somewhat greater degree (Chopra & is considerably larger. In haplolepideous species, the Bhandari 1959; Chopra & Sharma 1959; Wende- three IPL cells are of roughly equal size. roth 1931). Our unpublished observations on species The peristomial formula of mature Funaria-type of Polytrichum, Pogonatum, and Atrichum confirm peristomes is uniformly 4:2:4. The formula for that additional anticlinal divisions occur early in Bryum-type peristomes ranges from 4:2:2 to 4:2:12, development and result in twice the number of cells but 4:2:4-8 is most common (Edwards 1984; Shaw in each amphithecial layer as compared to arthro- & Robinson 1984). As demonstrated in this study, dontous species. Otherwise, however, the sequence the haplolepideous peristomial formula ranges from of alternating anticlinal and periclinal divisions is 4:2:3 to 4:2:6 and thus overlaps with the Bryum remarkably like that which occurs in arthrodontous type. However, the sequence of cell divisions that mosses. results in a 4:2:6 Bryum-type peristome differs from At what developmental stage, then, do haplole- the sequence leading to a haplolepideous peristome pideous peristomes diverge from diplolepideous with the same formula, as described above. It there- peristomes? In haplolepideous species, the eight fore appears that the overlap in the range of peri- original IPL cells undergo asymmetrical anticlinal stomial formulae between Bryum-type diplolepid- divisions which result in a larger cell and a smaller eous and haplolepideous peristomes may be due to cell adjacent to each PPL cell. This generally begins convergence, and not homology. Asymmetrical di- when the amphithecium consists of three layers (e.g., visions in the IPL, and disalignment of radial walls Fig. 6, 24, 34). In diplolepideous species, these di- in the IPL and PPL, features shared by mosses with visions in the IPL often do not occur until the am- Bryum-type and haplolepideous peristomes, may phithecium consists of at least four layers (Shaw et on the other hand be homologies uniting these two al. 1989). groups. The anticlinal divisions that occur in the IPL cells It is noteworthy that no diplolepideous peri- of the haplolepideous species are obviously asym- stomes have been described as having a 4:2:3 cell metrical. In diplolepideous peristomes of the Fu- arrangement when mature. Formulae of 4:2:2 and naria type (Shaw et al. 1989; Shaw & Robinson 4:2:4 do occur in Bryum-type peristomes, but the 1984), these anticlinal divisions are almost perfectly number of IPL cells is always an even number. The symmetrical and divide the eight IPL cells into 16 4:2:5 arrangements, as described here in Ditrichum cells of uniform size. In Bryum-type diplolepideous pallidum and Dicranum, apparently do not occur peristomes, however, the divisions are asymmet- in diplolepideous mosses. rical, yet not so strongly so as in the haplolepideous Haplolepideous peristome teeth develop from species (Shaw et al. 1989). It appears that Bryum- periclinal wall pairs of the IPL and PPL. In diplo- type peristomes are intermediate in this regard but lepideous peristomes, the outer or exostome teeth we have not yet made quantitative observations. develop from OPL and PPL wall pairs and the inner In diplolepideous peristomes of either the Fu- or endostome develops from IPL and PPL wall pairs. naria or Bryum type, every one of the 16 IPL cells It has long been recognized, based on these obser- that result from anticlinal divisions in the original vations, that the diplolepideous endostome is ho- eight cells (whether symmetrical or not) all undergo mologous in position to the haplolepideous peri- another anticlinal division. As a consequence, the stome. Our observations demonstrate that the 16 peristomial formula changes from 4:2:2 to 4:2:4 haplolepideous peristome teeth develop from the without a well-defined 4:2:3 stage (Shaw et al. 1989). median inner periclinal walls of each of the 16 PPL In the haplolepideous species, a 4:2:3 stage results cells. There is no peristomial wall deposition where 324 THE BRYOLOGIST [VOL.92 adjacent PPL cells meet. Bryum-type endostome ACKNOWLEDGMENTS segments, in contrast, develop in the positions where PPL cells meet. Because of the convex This study was supportedby NSF grantBSR-8506992. adjacent shape We thankM. Turnerfor his able technicalassistance, and of the PPL cells and the triangular shape of IPL cells A. Newton for providing the Colorado material of Di- that fit into the angles between adjacent PPL cells, cranumrhabdocarpum. Bryum-type endostome segments are vertically keeled at this point. Haplolepideous peristome teeth LITERATURECITED are not keeled because the PPL cells do not usually become or convex. In terms of where the BLOMQUIST,H. L. & L. L. ROBERTSON.1941. The de- enlarged in wall velopment of the peristome Aulacomniumheter- depositions ccur, haplolepideous peristome ostichum. Bulletin of the Torrey Botanical Club 68: teeth are homologous to the cilia of Bryum-type 569-584. endostomes. CHOPRA,R. H. & N. N. BHANDARI. 1959. Cyto-mor- Is there a sequence of divisions in the peristomial phological studies of the genus AtrichumPalis. Re- which is to and shared with search BulletinPunjab University 10: 221-231. layers unique by species - & P. D. SHARMA. 1958. of the structure? Edwards Cyto-morphology haplolepideous peristome (1979) genus PogonatumPalis. Phytomorphology8: 41-60. argued for monophyly of haplolepideous mosses be- & . 1959. Cytomorphologicalstudies of cause of a uniform 4:2:3 peristomial formula at ma- OligotrichumLam. et De Cand. Journalof the Indian turity, and the alignment of every third anticlinal BotanicalSociety 38: 400-414. IPL wall with a wall in the PPL. Our observations EDWARDS,S. R. 1979. Taxonomic implications of cell patternsin haplolepideousmoss peristomes,pp. 317- indicate that neither trait is consistent at maturity 346. In G. C. S. Clarke& J. G. Duckett (eds.), Bry- even among the six species described here. How- ophyte Systematics.New York. ever, the sequence of divisions leading to the 4:2:3 . 1984. Homologies and inter-relationsof moss cell even if additional IPL divisions peristomes,pp. 658-695. In R. M. Schuster(ed.), New arrangement, Manual of Vol. 2. is to and shared these Bryology, Tokyo. occur later, unique by hap- EVANS,A. W. & H. D. HOOKER,JR. 1913. Development lolepideous species. Consequently, developmental of peristome in Ceratodonpurpureus. Bulletin of the data do unite haplolepideous mosses. Monophyly, TorreyBotanical Club 40: 97-109. on the other hand, is only indicated if this devel- FLEISCHER, M. 1902-1923. Die Musci der Flora von von mit an de- Buitenzorg zugleich Laubmoosflora Java opmental similarity represents evolutionarily Beriicksichtigungaller Familien und Gattungender ge- rived characteristic (synapomorphy). If the devel- samten Laubmooswelt,Vols. 1-4. opmental sequence characterizing haplolepideous JOHANSEN,D. A. 1940. PlantMicrotechnique. New York. peristomes is in fact primitive in arthrodontous MITTEN,W. 1859. Musci Indiae Orientalis. An enu- meration of the mosses of the East Indies. Journalof mosses, there would be no evidence for monophyly the Proceedingsof the Linnaean Society (London), of the Haplolepideae. It is still premature to hy- Supplementin Botany 1: 1-171. pothesize evolutionary polarity of the develop- MUELLER,D. M. J. 1973. The peristome of Fissidens mental pathways we are describing. We have in limbatus Sullivant. University of CaliforniaPublica- tions in 63: 1-34. progress developmental studies of putative out- Botany of the arthrodontous mosses Po- PHILIBERT, H. 1884a,b. De l'importance du peristome groups (including pour les affinits naturellesdes mousses. Revue Bryo- lytrichales and Sphagnum) which should provide logique 11: 49-52, 65-72. evidence bearing on such questions. 1884c-1902. Etude sur le pbristome. Revue In a previous paper (Shaw et al. 1987) we argued, Bryologique11: 81-87 (1884); 12:67-77, 81-85 (1885); based on information, that the peri- 13: 17-27, 81-86 (1886); 14: 9-11, 81-90 (1887); 15: developmental 90-93 16: is in 6-12, 24-28, 37-44, 50-60, 65-69, (1888); stome of Diphyscium foliosum haplolepideous 1-9, 39-44, 67-77 (1889); 17: 8-12, 25-29, 39-42 spite of its unusual structure at maturity. The peri- (1890); 23: 36-38, 41-56 (1896); 28: 56-59, 127-130 stomial layers attain the haplolepideous 4:2:3 cell (1901); 29: 10-13 (1902). arrangementjust prior to maturity, but this arrange- SAITO,S. 1956. Studieson the developmentof the peri- the in Dicranum ment is obscured additional divisions stome in Musci. II. On peristome ultimately by japonicum Mitt. Botanical Magazine,Tokyo 69: 53- in the IPL, and extreme swelling of PPL cells. Pres- 58. ent results indicate that neither of these latter char- S& S. SHIMOZE.1954. Studieson the development acteristics is unusual for haplolepideous mosses. of the peristomein Musci. I. On the peristomein Bar- Additional IPL divisions occur in five of the six tramia crispata Schimp. (In Japanese, English sum- mary.)Botanical Magazine, Tokyo 68: 55-60. species described in this paper, and in Dicranum SHAW,J. 1985. Peristome structure in the Mitteniales the PPL cells become noticeably swollen. Although (Ord. Nov.: Musci), a neglected novelty. Systematic the extreme swelling of PPL cells that characterizes Botany 10: 224-233. - & L. E. ANDERSON.1988. Peristome D. foliosum sets that species apart from those de- development in mosses in relationto systematicsand evolution. II. scribed here, the interpretation that Diphyscium is Tetraphispellucida (Tetraphidaceae). American Jour- fundamentally haplolepideous is strengthened by the nal of Botany 75: 1019-1032. present observations. - , - & B. D. MISHLER.1987. Peristomede- 1989] SHAW ET AL.: PERISTOMEDEVELOPMENT IN HAPLOLEPIDEAE 325

velopment in mosses in relation to systematics and STONE,I. G. 1961. The gametophore and sporophyte of evolution. I. Diphysciumfoliosum (Buxbaumiaceae). Mittenia plumula (Mitt.) Lindb. Australian Journal of Memoirs of the New York BotanicalGarden 45: 55- Botany 9: 124-151. 70. VITr,D. H. 1984. Classificationof mosses, pp. 696-759. - , - & - . 1989. Peristomedevelopment In R. M. Schuster (ed.), New Manual of Bryology, Vol. in mosses in relationto systematicsand evolution. III. 2. Tokyo. Funariahygrometrica, Bryum pseudocapillare, and B. WENDEROTH,H. 1931. Beitriige zur Kenntnis des Spo- bicolor.Systematic Botany 14: 24-36. rophyten von Polytrichumjuniperinum Willdenow. - & H. ROBINSON.1984. On the development,evo- Planta 14: 244-385. lution and function of peristomesin mosses. Journal of the Hattori BotanicalLaboratory 57: 319-335.