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Morphology and Homology of the Peristome Teeth in Hymenodon and Hymenodontopsis (Rhizogoniaceae: Musci) Author(S): Jonathan Shaw and Lewis E

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Morphology and Homology of the Peristome Teeth in Hymenodon and Hymenodontopsis (Rhizogoniaceae: Musci) Author(S): Jonathan Shaw and Lewis E Morphology and Homology of the Peristome Teeth in Hymenodon and Hymenodontopsis (Rhizogoniaceae: Musci) Author(s): Jonathan Shaw and Lewis E. Anderson Source: Systematic Botany, Vol. 11, No. 3 (Jul. - Sep., 1986), pp. 446-454 Published by: American Society of Plant Taxonomists Stable URL: http://www.jstor.org/stable/2419081 Accessed: 17/11/2010 11:05 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. 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Copyright1986 by the American Society of Plant Taxonomists Morphology and Homology of the Peristome Teeth in Hymenodon and Hymenodontopsis (Rhizogoniaceae: Musci) JONATHAN SHAW and LEWIS E. ANDERSON Departmentof Botany,Duke University,Durham, North Carolina 27706 ABSTRACT. Hymenodonand Hymenodontopsisare two small genera in the Rhizogoniaceae with single peristomestraditionally thought to be endostomes. Based on cellular patternson the inner and outer surfaces,the peristome of Hymenodontopsisis confirmedas an endostome. The single peristomes of Hymenodonsericeus and H. angustifoliusare, however, exostomes, with peristomial formulaeof 4:2. The formerspecies has a preperistomeformed from the OPL-2. Hymenodonparvulus has a double peristome and this, combined with distinctivegametophytic morphology, indicates that the species is misplaced in Hymenodon.A placement in Powellia(Racopilaceae) is accepted with hesitation. The Rhizogoniaceae are a medium-sized ratherthan reticulations.Reticulate ornamen- familyof mosses consistingof seven genera and tationoccurs on the teeth in several other mor- about 45 species. Morphological featuresthat phologically similar rhizogoniaceous genera define the familyinclude lateral inflorescences (e.g., RhizogoniumBrid., Mesochaete Lindb., and on rather highly branched plants, sharply GoniobryumLindb.) (Shaw 1985b). In Hymeno- toothed leaves that are often bistratose along don Hook.f. & Wils., with about seven species, the margins,and rounded-hexagonal leaf cells and HymenodontopsisHerz., with two species, generallyhaving thickenedwalls. Most species the peristomeconsists of a single ring of teeth are distributedin the Southern Hemisphere in which have been interpreted as endostomes moist tropical or subtropical forests. (Brotherus1924). Details of peristomestructure constitute the It is not always a simple matterto distinguish mostimportant characters defining the families exostomes and endostomes when one of the and orders of mosses (Dixon 1932). Peristomes two is absent. Shaw and Rohrer (1984) inves- of species classifiedin the Bryales,to which the tigated the problem by studying cellular pat- Rhizogoniaceae traditionallybelong (Brother- terns characterizingthe outer and inner sur- us 1924; Vitt 1982, 1984), are diplolepideous faces of exostomes and endostomes in mosses with a reticulate ornamentationon the outer where the homology of the layers is clear, i.e., surfaces of the exostome teeth (Shaw 1985b). when both rings of teeth are present. Their The peristome is generally double, consisting study was built upon the foundation laid by of well-developed exostome and endostome, Edwards (1979, 1984), who showed that the although in some species and genera one or the number of cells in each of the three concentric other ring of teeth may be reduced or absent. layers giving rise to peristome teeth in a de- The Rhizogoniaceae are rather heterogeneous veloping capsule can be inferredfrom the pat- in peristomestructure compared to other bry- terns of lines on mature peristomes. For ex- alian families in that two of the genera (Pyr- ample, Edwards showed that the single ring of rhobryumMitt. and CryptopodiumBrid.) have haplolepideous peristome teeth are derived cross-striationson the outer exostomial surface fromtwo cells on the outside for every three FIGS. 1-6 SEM photographsof peristomestructure. 1-2. Hymenodontopsisstresemannii, endostome. 1. Out- er surfacewith the capsule rim visible at the bottom.2. Inner surface. 3-5. Hymenodonsericeus, exostome. 3. Outer surfacewith the capsule rim visible at the bottom.The basal membrane consists of the fused bases of the teeth and a pre-peristome.4. Outer surfaceabout midway up a tooth. 5. Inner surfaceabout midway up a tooth. 6. Hymenodonangustifolius, exostome outer surface; a pre-peristomeis absent. Scale on 1, 2 = 100 ,um;scale on 3, 6 = 40 ,um;scale in 4, 5 = 20 ,um. 446 1986] SHAW & ANDERSON: PERISTOME TEETH 447 7 -- i,A l. ~~~~~~~9-L A.W s 448 SYSTEMATIC BOTANY [Volume 11 s~A -#} 04~~~~~~~0 FiGs. 7-8. SEM photographsof the exostomein Hymenodonangustifolius. Outer (7) and inner(8) surfaces aboutmidway up a tooth.Scale = 10 ,um. cells on the inside. Shaw and Rohrer(1984) are thoughtto have single,endostomial peri- foundthat exostome teeth consist of remnants stomes,the teethare rathermassive and have of fourcells on the outsidefor every two on the superficialappearance of exostomes.In theinside. Endostomes, however, consist of two addition,a preliminarysurvey of peristome cells on the outsidefor every two, four,six, structurein severalspecies reveals significant eight,or 10 cells on theinside. The numberof inter-specificmorphological heterogeneity. cellscontributing wall materialto endostomes Therefore,this study was undertakento clarify on theirinner surfaces varies from two to 10 themorphology of the peristome teeth in three (or veryrarely up to 14-Shaw 1985a) but is speciesof Hymenodonwhich appear to encom- alwaysan even number.Thus, exostomes and pass the variationfound in the genus.In par- endostomescan be distinguishedby theirdif- ticular,our goal was to determinewhether the feringcell patternson theouter and innersur- teethin these species are homologousto the faces.When examiningexostome teeth, they exostomes,or endostomes,of diplolepideous consistof fourcolumns of cell wall remnants peristomes.In addition,one speciesof Hymeno- on theouter surface for every pair of teeth, and dontopsiswas examinedto determinethe ho- thereis thus a median verticalline on each mologyof its singleperistome, which is more toothas well as a verticalline betweeneach delicatethan those of species in Hymenodon.We tooth(visible where the teeth join at thebase). use theterm homology in thesense of the teeth Since thereare only two columnsof cell wall developingfrom the same cell layersas either remnantsfor each pairof endostome segments, an exostomeor endostome. thereis also a medianvertical line on each seg- ment,but there are no linesbetween segments MATERIALS AND METHODS on the outersurface. (In accordancewith ac- The peristomes of three species of Hymeno- ceptedterminology in bryology,processes of donwere investigated:H. angustifoliusLac., H. an exostomeare called teeth,and thoseof an sericeus(Dozy & Molk.) C. M., and H. parvulus endostomeare called segments.)Study of cel- Bartr.Hymenodontopsis stresemannii Herz. was lularpatterns allows one in mostcases to dis- examined as a representativeof that genus. All tinguishexostomes from endostomes when available specimens of these four species in onlyone ringis presentand developmentalin- DUKE, NY, and US were examined by light formationis notavailable. microscopy and representatives were then Althoughtraditionally species of Hymenodon studied with SEM. Only one fruitingspecimen 1986] SHAW & ANDERSON: PERISTOME TEETH 449 each of Hymenodonparvulus (Brass 30348-NY) and Hymenodontopsisstresemannii (Weber & McVean B-31974-US) were available. The fol- lowing additional specimens were studied with SEM: H. sericeus(Fleischer, Musci Frond. Ar- chip. Indici 35-US; Kurz 873-NY) and H. an- gustifolius(Carr 15604-NY; JacobsB-962-NY). There appeared to be relativelylittle infra-spe- cific variation in peristome morphology in H. sericeusand H. angustifolius. For SEM study, capsules were thoroughly moistened, cut longitudinally, and the distal portions of the capsules placed on glass slides in water with the outer surface of one half up and the inner surface of the other up. After examinationwith a light microscope,the slides were allowed to dry with a weight placed on the cover slip to avoid curling of the peristome teeth. The specimens were then transferredto an aluminumstub, coated with carbonand gold, and examined at 15 kV. RESULTS The single peristomeof Hymenodontopsisstre- semanniiis hyaline,thin, and very delicate (figs. 1, 2). A basal membraneextends 35-50 ,umhigh fromthe capsule rim and 16 slender teeth
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