An Essay on Species Concepts Developed during Revisionary Studies Author(s): Richard H. Zander Source: The Bryologist, Vol. 88, No. 3 (Autumn, 1985), pp. 215-220 Published by: American Bryological and Lichenological Society Stable URL: http://www.jstor.org/stable/3243031 Accessed: 09-06-2015 19:53 UTC

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This content downloaded from 192.104.39.2 on Tue, 09 Jun 2015 19:53:07 UTC All use subject to JSTOR Terms and Conditions The Bryologist 88(3), 1985, pp. 215-220 Copyright? 1985 by the AmericanBryological and LichenologicalSociety, Inc.

An Essay on Species Concepts Developed During Revisionary Studies

RICHARD H. ZANDER BuffaloMuseum of Science, Buffalo,NY 14211

The International Code of Botanical Nomencla- approach. Herbarium contributes to an ture carefully avoids incorporation of a species con- understanding of the biology of a group through cept in the promulgated rules. We are given, instead, evaluations based on long familiarity (through ob- a structure of ranks with that of species as basal. A servation in the herbarium and in the field) with nomenclaturally correct name may have various de- morphological and phenological variation and their grees of biological substance, however, and only associated habitat and distribution. Thus, taxonom- rarely is such a name based on qualitative or quan- ic study itself reveals biological facts about organ- titative studies demonstrating that it represents a isms. But, because alpha-taxonomy is, for the most valid inference of the existence of a more or less part, simply well informed opinion, species con- clearly differentiated group of individuals in nature. cepts of taxonomists may differ according to differ- The period of exploratory botany of the last two ences between the taxonomists themselves: by how hundred years resulted in many geographic species well-informed they are, how much weight they give names with little species concept associated with new data, how inclined they might be to introduce them other than that their authors could not re- novelties, and various other tendencies and atti- member seeing anything quite like the representa- tudes. Given this situation, practical bryophyte tax- tive specimens before, at least from that area of the onomists generally do not espouse a "best" species world. The writers of floristics manuals and world concept, or even assume such exists, but show a revisions recognized that many species names from tolerance and acceptance of other workers' attempts the exploratory effort must be relegated to synon- to present their admittedly subjective studies as ymy because they are represented by specimens that contributions towards a useful taxonomic frame- intergrade on a morphological continuum that is work. called variability. This variation is generally sup- A species definition is a piece of guesswork-a posed to have a biological explanation. Neverthe- hypothesis that ties together observations and which less, acceptance that an intergrading spectrum of might be tested by future study with appropriate morphotypes requires synonymy of names is basi- controls. It is not a thing in nature that can be mea- cally a philosophical stance on the part of the tax- sured or studied. To demonstrate how species con- onomist. Seldom is there any experimental dem- cepts are important in representing the results of onstration of biological continuity between herbarium study at the alpha-taxonomic level, I will morphotypes. In fact some taxonomists are appar- review how my own concepts have developed over ently able to tell when the continuum is too broad 15 years of work with the and then dis- and surely cannot represent only one species. Local cuss the various papers in the symposium with this floristic manuals may accept taxa that were not pre- experience in mind. It will be evident that my great- viously recognized in world revisions (e.g., Crum & est concern is with the way nomenclature deals or, Anderson 1981 versus Zander 1972 regarding syn- more often, avoids dealing with species concepts. onymy of Leptodontium excelsum Sull.). This may Presentation of nomenclatural novelties. New taxa be because certain taxa are more clearly distinguish- I have described have been conceptualized in con- able in some areas of the world than in others or texts of both splitting and lumping. Names in the are supposedly distinguishable if one looks close genera Fissidens (Zander 1969), Desmatodon (Zan- enough. Also, the descriptions and circumscriptions der & Crum 1977), (Zander & Steere 1978) of species and supraspecific taxa in regional treat- and Splachnobryum (Norris & Zander 1981) were ments may be different from those of the same taxa offered based on apparently unique combinations in world revisions in that the former are often based of character states but without evaluation of the solely on the local representation. These problems, value of such characters in general taxonomy of the and still others, are characteristic of the period of groups, which would be impossible in any case with- revisionary studies when synthetic species concepts out extensive revision. Names in Leptodontium begin to be established. (Zander 1972) and Trichostomum (Zander 1982c) One of the tenets of herbarium taxonomy is that were published for taxa that proved clearly distinc- much can be discovered about bryophyte biology tive in the context of regional revisions. New names, without recourse to a more lengthy experimental combinations and statuses were also given under 007-2745/85/215-220$0.75/0 This content downloaded from 192.104.39.2 on Tue, 09 Jun 2015 19:53:07 UTC All use subject to JSTOR Terms and Conditions 216 THEBRYOLOGIST [Volume 88 narrow, conservative species concepts in poorly formation, the taxa were distinguished at the understood genera: e.g., Didymodon (Zander 1978b), infraspecific level, a solution that better represents Tortella (Zander & Hoe 1979); and, in somewhat the perceived biological relationship. Sterile speci- better known or recently revised situations: Didy- mens can then be annotated "Leptodontium vitic- modon (Zander 1982b), Oxystegus (Zander 1982a, ulosoides sensu lato." A fact supporting this reso- 1983c), and Hyophila and Leptodontium (Zander lution is that a third variety, var. exasperatum (Card.) 1983b). The genus Pseudocrossidium was emended Zand., based on differences in laminal papillae mor- (Zander 1979a) to include species previously in Bar- phology, is represented by both anisosporous and bula and Tortula in order to recognize what was isosporous collections. This is an example ofa species hypothesized to be a monophyletic group evolving concept tailored in part to optimize the biological towards morphological modifications for photosyn- significance of its associated name. thesis. Clearly, the sophistication of the species def- The Code requires, through the principle of no- initions offered in the papers cited above depended menclatural priority, that taxa be discontinuous, at on the extent of knowledge of the group. least to the extent that the taxonomist must be able Morphological variation. Noguchi's (1956) paper to refer type specimens to the appropriate taxonom- offering extensive synonymy for species of Scope- ic group. For groups that appear to be nondiscon- lophila was the conceptual model at the species level tinuous, but very distinctive at the morphological for my treatment of this genus in the New World extremes, I at first (Zander 1978a, 1982d) used a (Zander 1967). The two species recognized (S. lig- taxonomically informal way of designating the ex- ulata (Spruce) Spruce, S. cataractae (Mitt.) Broth.) treme morphotypes (the species name sensu lato, are easily distinguished but are rather variable with followed by the term "facies" and the name of the respect to several characters. I pointed out two ex- earliest or the most familiar synonym, the type spec- tremes of morphological variation in S. ligulata: a imen of which approximated the extreme morpho- "hydric" form with loosely pulvinate habit and flac- type). This proved ungainly. Informal names for cid, spreading leaves with the upper leaf cells thin- bryophyte morphological variants, such as the walled and the enlarged basal cells often extending "Idealtypen" of Herzog (1907) or the "modificatio" more than halfway up the leaf, and a "montane" system of Buch (1922), have certainly never proved form with a densely pulvinate habit and narrow, popular. I then (Zander 1981, 1982b, 1983a; Zander firm, appressed leaves with the upper cells mostly & Eckel 1982) decided that non-discontinuous but thick-walled and the enlarged basal cells mostly con- distinctive infraspecific variants are better named fined to the lower third of the leaf. The existence of using standard nomenclature. I used a method that intra-specific intergradation between morphological assigned a particular varietal name to a distinctive extremes is discussed in succeeding papers on other morphotype at one end of a perceived continuum genera as part of a "species concept" that recognized of variation using the earliest type specimen (of this as a common occurrence in the Pottiaceae. available names at the varietal level, including that Species definitions incorporating a gradual change of the typical variety) that was clearly representative in several character states--this often correlated with of that morphotype. Once all varieties were named, stature-were recognized in the genera Lep- all remaining heterotypic names were assigned to todontium(Zander 1972), Gymnostomum,Hyme- synonymy under the species name sensu lato. This nostylium, and Molendoa (Zander 1977, Zander & contravenes no nomenclatural rules and provides Eckel 1982), Didymodon (Zander 1978b, 1982b), taxonomically acceptable varietal names without Bryoerythrophyllum (Zander 1978a), and Neohy- having to invent an artificial boundary with which ophila (Zander 1983a). to segregate all type specimens included in the species Leptodontiumviticulosoides (P. Beauv.) Wijk & sensu lato. Identifications of specimens may now Marg. var. viticulosoidesand L. viticulosoidesvar. well represent the species concept in that the species sulfureum (Lor.) Zand. (as var. panamense (Lor.) name sensu lato can be used for specimens of in- Zand.) are very close morphologically but differ termediate morphology. (Zander 1972) in sexuality (monoicous, including Name enhancements. As I have previously point- apparent rhizautoicy, vs. dioicous) and spore size ed out (Zander 1982b), the Code does not provide (anisosporous vs. isosporous). For Leptodontium, for different names for different species concepts these are rather important characters, and the two that include the same type specimen, and, through taxa may have been recognized at the specific level the requirement of the type method for working were it not for the fact that collections of the two with the nomenclature of infraspecific taxa, it at taxa are generally sterile and the gametophytes are least implies that all taxa are discontinuous. I have for the most part indistinguishable. To avoid la- attempted to deal with this in several ways, none belling the many sterile collections simply "Lepto- of which is completely satisfactory. dontium sp.," an appellation that conveys little in- The terms "columbarium" and "parochialis" were

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introduced in a treatment of Didymodon (Zander ies and inferences about population biology and the 1978b). The former was appended to the names of sources of variability. I am an unabashed adherent taxa to identify those suspected to be pigeonhole of "general purpose taxonomy" (for instance, as is species definitions, i.e., segregates on a continuum discussed by Raven 1974), and I think this attitude of morphological variation. The latter was used for may be characteristic of how other herbarium tax- geographic or otherwise narrowly conceived species onomists of my generation have developed species with practically nothing known, or at least inferable, concepts. Given this, how might the new taxonomic about their biology and for which a previously pub- emphases of the symposium speakers contribute to lished synonym probably already exists. taxonomy for its own sake and for its contribution Because there are sometimes more than one dif- to biological understanding of the Bryophyta? ferent species definition attached to particular species names various authors, I have recommended by COMMENTARY (Zander 1982d) that the phrases sensu lato, sensu stricto and emendavit (with author's name and date Donoghue's "Critique.. ." clarifies the problems of publication) be more commonly used to better associated with the "biological species concept," and indicate exactly what an author or annotator of a his proposal for a "phylogenetic species concept" is specimen means in using such names. certainly challenging. I have in the past generally Parallel trends. In a treatment of Didymodon avoided discussion of phylogenetic relationships in (Zander 1978b), I presented a chart that demon- my papers because assignment of traits to "primi- strated possible parallel trends in speciation among tive" or "advanced" status seems either arbitrary several taxa in three sections of the genus. Certain or extremely problematical. The only way it ap- slots remained empty: a hygrophilic species for sect. peared to me that one can infer an evolutionary Vineales and a species with a propaguloid apex in relationship with any confidence is to assume that sect. Fallaces (as sect. Graciles). Although it is well a morphologically, and therefore probably evolu- known that it is dangerous to assume that species tionarily, complicated trait, for example, the chor- concepts useful in one group can be expected to date eye, the feather, or the seed habit, has a very apply in another, the discovery of collections with small chance of evolving twice in unrelated groups. one or the other morphological features given above I have not pursued this since I have not found many would certainly encourage recognition of a species complicated traits in below the family level along the same lines as in the other, assumably par- that cannot be considered possibly being due to par- allel evolving sections. allel evolution. Also, I can identify few transfor- Introducing new characters. Bryologists often mation series that are probably irreversible and am search for new characters that might help distin- uncomfortable with the idea of regarding rare or guish taxa that are similar, at least when sterile. The unique characters as almost surely apomorphic. genera of Pottiaceae proved to have rather distinc- There is no reason why morphologically gener- tive leaf color responses to various reagents (Zander alist daughter species cannot be derived from a 1980, 1983c), and characteristic dates of sporophyte species with a few rare characters, especially in bryo- maturation (Zander 1979b) that proved helpful in phytic taxa with morphological variation charac- placing Tortula plinthobia (Sull. & Lesq.) Broth., at terized by extreme reduction of the gametophyte. least, in the correct genus. The appearance of a particular character state in a Growth studies. Behavior in cultivation was sig- group is not necessarily through selection for a new nificant in uncovering heterophylly in Tortellafra- character but can also occur through selection against gilis var. tortelloides (Greene) Zand. & Hoe (Zander genes masking an old character. If the plesiomorph- & Hoe 1979). This threw light on a similar situation ic character is also masked in related groups (but is (Zander unpublished) in the var. fragilis (detailed perhaps present but masked in other members of below). A common garden comparing Tortula cainii the original group), the outgroup comparison is in- Crum & Anderson and the similar T. norvegica valid. For instance, leaves of Barbula unguiculata (Web.) Lindb. demonstrated (Zander & Eckel 1980) Hedw. are dentate in cultured specimens (D. Basile the apparent permanency of certain features of the & R. Zander unpublished). "Leaves dentate" is a former. rare character in the genus and might be expected In sum, my species definition is not one "form" to be derived. Thus, what may be a plesiomorphic or model of what a species is supposed to be but character can be "advanced" through desuppression instead attempts to represent what is known about into false apomorphy. How common is this? Could a group biologically through appropriate nomencla- the well-known Weissia-Astomum and Pottia-Tor- ture and discussion, and, although based largely on tula transformation series actually be caused by morphological observation of herbarium speci- gradual desuppression ofperistome characters rath- mens, is refined through simple biosystematic stud- er than the more common interpretation of these

This content downloaded from 192.104.39.2 on Tue, 09 Jun 2015 19:53:07 UTC All use subject to JSTOR Terms and Conditions 218 THEBRYOLOGIST [Volume 88 as reduction series (through suppression or loss of phylogenetic and epigenetic evaluations. In general, traits)? I find his species concept attractive and certainly The absence of a mutation ("leaves smooth") has worth testing. His suggestion that developmental quite different phylogenetic significance than does events may strongly affect the phenotype is worth- the masking of a character ("leaves lacking pa- while. I agree with his estimate that much present pillae"). One or more mistakes in this fashion in taxonomic study is "below the level" at which good evaluating character states might be multiplied into taxonomic judgments can be made. In fact, I think a series of spurious assignments of plesiomorphy there are many papers in the literature that attempt and apomorphy through cladists' method of "re- to solve problems in genetics and population biol- ciprocal illumination." Little is known about the ogy quite inappropriately using the techniques of genetic basis of character expression in the bryo- alpha taxonomy. Mishler's advocacy of many cri- phytes, and simple features dependent on one or teria for evaluating species ranking is admirable. I few alleles are, in any case, little liable to obey a do not feel, however, that "simple observation" is rule of parsimony. This is not to say that tentative sufficient to show that diversity in nature is discon- assignment of advanced and primitive character tinuous. He may be confusing language with per- states is not usually well-informed and of inferential ceived phenomena. Perceptions are more easily dealt value, since we all make some hypotheses about with if comprehended as relationships between dis- phylogeny and this influences our taxonomy, but to crete objects, but the phenomena represented by what extent should we base our systematics on it? linguistic abstractions like "species" and even many The first step in phylogenetic analysis is surely the "real" things (like the "upper part" of this page) are longest. quite vague in circumscription. I ascribe to a kind Cladistics probably will have much to offer when of nominalism that recognizes the value of inference it has passed through its difficult quasi-ideological and the mere convenience of abstract terms. Mishler phase. I look forward to classifications of bryophyte promotes an across-the-board realism (in the phil- groups advanced through cladistic studies. Unfor- osophical sense) that I do not think is widely shared tunately, the present bryophyte genera and species among taxonomists. I, for one, infer that species of are mostly artificial constructs and probably not very various sorts exist, being aggregations of biologically valuable for use in developing cladograms. Bryo- related individuals in nature for which our species phyte taxa may not only be groups of rather unre- definitions (developed as hypotheses based on ob- lated organisms, but morphological terminology is servations of comparatively few representative in- inexact and misleading. For instance, taxa described dividuals) serve as models; but I have faith in the as "dioicous" may include all or many rhizautoi- expected utility of that inference, not in the concept cous species. Cladistic work based solely on infor- of "species" itself. Mishler's requirement of the rec- mation from the literature involving bryophyte ognition of "theoretically meaningful taxa" seems groups that have not been monographed or other- to make theory itself the test of the validity of the wise recently revised ought to be viewed with much species concept. reservation. Even the word "character" has all the Mishler's discussion of the lack of correlation be- vagueness of definition as have "species" and "pop- tween reproductive method and range in Tortula ulation." may not demonstrate a noncorrespondence, since The "phylogenetic species concept" has much to spores may be little more genetically heterogeneous recommend it. Its success in bryology, I believe, than other diaspores. As I have previously noted will depend on how convenient cladistically derived (Zander 1984), crossing between two different ga- species concepts are for use by bryologists in general. metophytes, even in dioicous species, may simply As to ranking, a classification based entirely on ge- involve crossing between the products of the same nealogical principles will remain of interest only to sporangium. This is equivalent to rather close in- specialists in phylogeny unless it has the utility of breeding in the flowering . Also, one might the present phenetic system. It remains cloudy, for expect that crossing between gametophytes is al- many taxonomists at least, just how certain one can most always within one microhabitat because of the be that clades- constructed through the intuitive short sperm gene flow distance, which inhibits hy- processes of (1) selecting the proper outgroup and bridization between different ecotypes. This as- (2) correct assignment of advanced and derived sumes that spores of different ecotypes seldom pro- characters-reflect actual ancestry. Any amount of duce sexually mature gametophytes in environments uncertainty in cladistic techniques must be weighed other than those for which they are adapted. Thus, against whatever uncertainties are involved in using spores may be seen as numerous, small propagula phenetic principles to group and rank taxa. of value for fitness in habitats with much available Mishler's contribution introduces a somewhat colonizable surface, while asexual species are adapt- more complicated species concept involving both ed for reasons of atelochory (Zander 1979a) in

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"patchy" or narrowly circumscribed habitats, or for have been construed on phenotypic grounds is, in conservation of biomass in harsh environments. In my opinion, true but idealistic. There is a time for any case genetic variability of diaspores may play putting forward a biologically based species defi- little part in determining range differences in species nition just as there is a time for the geographic of Tortula. species of exploratory floristics and those developed Wyatt's paper discussing recent discoveries from in revisionary studies. population biology brings the sibling species prob- The "reverse geographic argument," as shown for lem to bryology with a vengeance. I am happy to Mielichhoferia species, is very interesting, and rates see that he does require morphological markers for being pursued for other similar pairs or series as the recognition of genetically diverse but morpho- floristic information is amassed for them. Regarding logically similar taxa. Likewise, I appreciate reading this, I once wondered if there was not a genetic that "the naming of ... all genetic variants as species relationship between Tortella tortuosa (Hedw.) should be avoided" and that the evaluation of a Limpr. and T. fragilis in view of a somewhat similar monographer of the level of morphological differ- habitat and range match, and the fact that fragile, ence that constitutes a species within a group should leaved variants of the former are apparently com- be respected. I have no argument with most of what mon in northern North America. A close study Wyatt has written but hope that future systematic (Zander unpublished) of herbarium specimens, studies involving non-morphological variation will however, demonstrated that young plants of T. fra- be reflected in only those nomenclatural changes gilis lack the bistratose apex with elongate marginal that preserve the convenience of scientific names in cells found in the upper leaves of mature plants. If representing important biological differences at a this developmental variation is taken into account, level useful to most biological researchers. Whether the two species are quite distinct when mature and electrophoretic analyses demonstrate real biological can always be separated when immature by the ap- differences or are essentially neutral in regard to pearance of the leaf apex, which in T. tortuosa has evolution, their taxonomic value ought to be a short awn several cells in length, and in T. fragilis weighted in respect to other characters so as not to has an apiculus of one to three cells. This is sup- compromise a generalist taxonomy. ported by culture experiments demonstrating sim- Stark's case study of phenology (and reproductive ilar heterophylly in T. fragilis var. tortelloides morphology and branching patterns) is an excellent (Greene) Zand. & Hoe (Zander & Hoe 1979). example of the refinement of species concepts with additional The fact that the biological knowledge. SUMMARY two species studied show clear differences in repro- ductive behavior and morphology gives more value With the appearance of monographic and revi- to the morphological characters used in their tax- sionary works over time, it is becoming possible to onomy. Because characters associated with repro- do studies that link biological facts of phenology, duction directly influence fitness, Stark's treatment development, ecology, and population biology to is a contribution to understanding of species as bi- species concepts, and to use such knowledge in eval- ological entities. Because this study was done at only uating the degree to which particular species defi- one site, however, the conclusions reached in the nitions are useful for the purposes of biological study paper may not apply equally across the distribu- as a whole. The implications of the theoretical ideas tional range of the taxa discussed. advanced by the symposium participants are far Of the symposium papers, Shaw's discussion of reaching, but their value to practicing taxonomists the relevance of ecology to species concepts is prob- and biologists in general can only be assessed through ably the most apropos to the interests of the prac- our application of the described techniques to actual tical taxonomist. The use of ecological data is com- problems. The Symposium does well in promoting mon among monographers and revisionists in and regularizing species concepts as tools in tax- developing species concepts, and Shaw provides a onomy. sensible perspective and details some interesting The drafts of the papers upon which I base this techniques. I applaud Shaw's assertion that classi- commentary give the reader the impression that fications cannot be proven or disproven, and agree each author has one species concept that they per- that classifications that reflect evolutionary history sonally feel is "best." This is surely not the case. would be more apt to group genetically related or- During the question and answer session of the sym- ganisms, which heightens the predictive value of the posium, Donoghue suggested that different disci- classification. Agreeably, he does not state that cla- plines may require different species concepts, and distics is the best or only way to determine geneal- because he is interested in phylogeny, he is con- ogy. His statement that it is important to demon- cerned primarily with a phylogenetic species con- strate some biological individuality for species that cept. But, he explained, if we are clear in discussing

This content downloaded from 192.104.39.2 on Tue, 09 Jun 2015 19:53:07 UTC All use subject to JSTOR Terms and Conditions 220 THEBRYOLOGIST [Volume 88 correspondences between phylogeny, ecology and so ()in North America and an annotatedkey forth, there would be no real problem dealing with to the taxa. Phytologia44: 177-214. . 1979b. Patternsof maturationdates Stark sporophyte discipline-oriented species concepts. Later, in the Pottiaceae (Bryopsida). THE BRYOLOGIST82: went further with this in suggesting that different 538-558. taxa may also require different species concepts. This . 1980. Acid-base color reactions:The status of flexibility on the part of our best modem bryological Triquetrellaferruginea, Barbula inaequalifolia and B. calcarea. THE BRYOLOGIST83: 228-233. theorists is comforting. . 1981. Descriptionsand illustrationsof Barbula, Pseudocrossidiumand Bryoerythrophyllum(p.p.) of ACKNOWLEDGEMENTS Mexico.Cryptogamie, Bryologie Lichenologie 2: 1-22. 1982a. Oxystegustenuirostris var. stenocarpus I thank Patricia Eckel and Norton Miller for helpful (Thor.)? comb. nov. includes Trichostomumspirale comments on preliminarydrafts of this paper. Grout.Miscellanea Bryologica et Lichenologica9: 72- 74. LITERATURECITED 1982b "1981." Didymodon(Pottiaceae) in Mex- ico and California:Taxonomy and nomenclatureof CRUM, H. & L. E. ANDERSON.1981. The Mosses of East- discontinuousand nondiscontinuoustaxa. Cryptoga- ern NorthAmerica, Vol. 1. ColumbiaUniversity Press, mie, BryologieLichenologie 2: 379-422. New York. . 1982c. Trichostomummolariforme sp. nov. and BUCH,H. 1922. Die ScapanienNordeuropas und Sibi- Atractylocarpusstenocarpus (Wils. in Seem.)comb. nov. riens, I. CommentationesBiologicae, Societas Scien- THE BRYOLOGIST85: 126-128. tiarum Fennica 1(4): 1-21. . 1982d. Practicalspecies concepts, pp. 7-11. In HERZOG,T. 1907. Studien iiber den Formenkreisdes P. Geissler & S. W. Greene (eds.), BryophyteTaxon- Trichostomummutabile Br. Nova Acta Academiae omy-Methods, Practices and Floristic Exploration. CaesareaeLeopoldino-Carolinae Germanicae Naturae Nova HedwigiaBeiheifte 71. Curiosorum73(3): 453-481, tab. 6-12. 1983a. A reevaluationof NeohyophilaCrum NOGUCHI,A. 1956. On some mosses of Merceya,with (Pottiaceae). THE BRYOLOGIST86: 156-157. special reference to the variation and ecology. Ku- . 1983b. Nomenclatural changes in Hyophila, mamoto Journalof Science, Services B, 2: 239-257. Leptodontium and Morina (Pottiaceae). THE NORRIS,D. H. & R. H. ZANDER. 1981. Splachnobryum BRYOLOGIST86: 156-157. limbatum sp. nov. from San Cristobal,Solomon Is- .1983c "1982." Leptodontium recurvifolium lands. THE BRYOLOGIST84: 404-407. (Tayl.)Lindb. is an Oxystegus.Lindbergia 8:185-187. RAVEN,P. H. 1974. Plant systematics 1947-1972. An- . 1984. Bryophytesexual systems:-oicous versus nals of the Missouri BotanicalGarden 61: 166-178. -oecious. BryologischeBeitraege 3: 46-51. ZANDER,R. H. 1967. The New World distributionof - & H. CRUM. 1977. Desmatodon steereanus,a Scopelophila (=Merceya). THE BRYOLOGIST405-413. new species of Pottiaceae from Peru. THEBRYOLOGIST 1969. A new speciesof Fissidensfrom the south- 80: 638-640. ern ?Appalachian Mountains. THEBRYOLOGIST 72: 406- - & P. M. ECKEL.1980. Tortulacainii: Additional 409. Ontario records and behavior in a common garden. 1972. Revision ofthe genusLeptodontium(Mus- THE BRYOLOGIST83: 209-211. ci) in? the New World. THE BRYOLOGIST75: 213-280. - & . 1982. Hymenostyliumrecurvirostrum The tribe var. and in British Co- -.1977. Pleuroweisieae (Pottiaceae, insigne Barbulaamplexifolia Musci) in Middle America. THEBRYOLOGIST 80: 233- lumbia,Canada. Canadian Journal of Botany60:1596- 269. 1600. . 1978a. A synopsis of Bryoerythrophyllumand - & W. J. HOE. 1979. Geographicdisjunction and Morinia (Pottiaceae) in the New World. THE heterophylly in Tortellafragilis var. tortelloides(= BRYOLOGIST81: 539-560. Sarconeurumtortelloides). THE BRYOLOGIST82: 84- .1978b. New combinationsin Didymodon(Mus- 87. ci) and a key to the taxa in North America north of -- & W. C. STEERE. 1978. Tortulascotteri sp. nov. Mexico. Phytologia41: 11-32. from the Northwest Territories of Canada. THE . 1979a. Notes on Barbulaand Pseudocrossidium BRYOLOGIST81: 463-467.

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