Four types of asexual reproduction in Plagiochila and the Plagiochilaceae are known: propagules, caducous leaves, gemmae and cladia. Plagiochila pluma Steph. has caducous leaves and teeth with regenerants. The terms for asexual reproduction modes in liverworts are briefly discussed and new definitions proposed

Piippo, Sinikka

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7Tropical Bryology 5: 7-10, 1992On the asexual reproduction of Plagiochila pluma Steph.Sinikka PiippoBotanical Museum, University of Helsinki, Unioninkatu 44, SF-00170 Helsinki, FinlandAbstract. Four types of asexual reproduction in Plagiochila and the Plagiochilaceae are known:propagules, caducous leaves, gemmae and cladia. Plagiochila pluma Steph. has caducous leaves andteeth with regenerants. The terms for asexual reproduction modes in liverworts are briefly discussedand new definitions proposed.Gemmae were reported by Piippo (1989)in apical and distal margins of a Western Melane-sian endemic, Plagiochila pluma Steph. of Sect.Kaalaasiae Carl. Asexual reproduction was notknown earlier in this section (cf. Inoue 1984). Thematerial, collected by Prof. Daniel H. Norris in theSolomon Islands in 1977 includes one specimenof P. pluma. In this specimen “far developedgemmae” can be seen on every leaf margin (Fig.1). It is the only specimen of P. pluma withcaducous leaves.The leaves of Plagiochila pluma are nottotally caducous but irregularly fragile to onethird to one half or, rarely, to two-thirds of the leaflength. Apical parts of the leaves, sometimes thewhole leaf, may be malformed and variable. Themarginal cells seem to have a very high potentialto regenerate and develop into short to fairly longgemmaling-like structures with one-lobeduniseriate “primary leaves” (cf. Fulford 1955a,1955b, 1956, Nechira 1968, 1983, 1987). Thiscapacity is not restricted to apical leaf margins. Ihave not, however, noticed rhizoids ingemmalings, as reported by the other authorsabove. When further developed, these gemmaling-like structures produce small 2-lobed leaves (Fig.1g). Many of the larger structures have becomedetached from the leaf margins. According toDegenkolbe (1938), in general the regeneratingcells are usually marginal, and they first developa protonema typical of gemmalings. Typically,gemmalings are similar to sporelings. Ingemmaling formation the gemma first swells,then a wall divides the original cell into two(Fulford 1955c). Through cell division andgrowth, a filamentous protonema is formed.Plagiochila pluma apparently reprodu-ces also by caducous teeth (cilia), because manybroken teeth of different length are visible. Someof these cilia are 2-seriate or wider at their apices,which is peculiar for cilia. Some “propagules” areproduced also at the base of cilia. The highregeneration potential seems to involve allmarginal cells and the cilia.Inoue (1984, 1987, 1988a, 1988b) dis-cussed the means of asexual reproduction inPlagiochila and the Plagiochilaceae. Four typesare known.  The two common modes of asexualreproduction in Plagiochila are by propagulesdeveloped on living leaves firmly attached to thestem, and by caducous leaves or leaf parts whichafter detaching may produce regenerants. Morerarely, the marginal teeth may be fragile, as in P.eggersii Inoue (Inoue 1988a). The propagules8(Brutsprösschen, leaf cladia) are produced main-ly from a single leaf cell on postical leaf surfaces(Carl 1933, Degenkolbe 1938, Schuster 1959,1984), and these can be considered as highlymodified regenerants (Schuster 1984). Mostcommonly the propagules occur in the apical leafparts; The marginal cells lack the ability to producepropagules. The propagules usually originatefrom cells divided into two daughter cells. Afterfurther divisions the daughter cells develop intoa structure with rudimentary leaves whichsuddenly develop into normal leaves. Sometimespropagules are only a few, but occasionally theyoccur in bundles.In many sections of Plagiochila asexualreproduction is lacking, but in others it is typicallyeither by caducous leaves or by propagules. InAsia caducous leaves are typical for Sect.Subtropicae Carl in, e.g., Plagiochila parvifoliaLindbg. and P. tjibodensis Schiffn. Propagulesare common in Sect. Contiquae Carl, inPlagiochila celebica Schiffn. ex Inoue, P.teysmannii Sande Lac., and in P. javanica (Swartz)Dum. In the Palaeotropics no species are knownwith modes of asexual reproduction other thancaducous leaves or propagules.Recently two other modes of asexualreproduction were reported in the genus Plagio-chila. Two species with gemmae, P. moniliformisSchust. (sect. Bidentes Carl) and P. subfragilisInoue (sect. Zonatae Carl), were reported fromVenezuela (Schuster 1978, Inoue 1988b). In P.subfragilis the teeth of leaf margins may be fragile,and their apices may produce 2-5-celled gemmae.The genus Xenochila of the Plagiochilaceae hasmulticellular gemmae which often have rhizoidsat leaf margins (Inoue 1974).In 1987 Inoue described a new genus ofthe Plagiochilaceae, Steereochila, with gemmi-ferous branch apices. These “propagules” arethread-like, one-layered and 1-4-seriate, and areformed from malformed leaves; or 3-4-layeredwith 1-2-celled protuberances, and are formedfrom malformed branches. Both these branchesand leaves are caducous. The former are not truepropagules but cladia (i.e. caducous branches).According to Inoue (1987), morphologicallythese leaves and branches are similar to propagu-les Because of lack of uniform terminology anddifficulties in determining Plagiochila plumawhether the asexual reproductive method inquestion concerns gemmae developing intogemmalings, or regenerating cells, I propose thefollowing terminology for hepatics:1. Propagules: plantlets developingfrom the laminal cells of non-caducous leaves.2. Cladia: caducous branches.3. Gemmae: various kinds of bodies(such as single- or multicellular, filamentous,globose, cylindrical, differentiated or indifferen-tiated from the other cells) occurring mainly atmargins of non-caducous leaves, or at shoot apicesor leaf axils.4. Regenerants: protonema and plan-tlets developing on caducous or fragile leaves.Distinguishing gemmae and regenerantsstill remains problematic in some cases, especial-ly when the caducosity of leaves is not obvious.Material studied (in addition to those listed byPiippo 1989): Solomon Islands. San Cristobal, Manighai,1977 Norris & Roberts 48957 (H).Acknowledgements.Prof. Timo Koponen is thanked for critical remarks on thetext. Dr. Carolyn Norris revised the English.Literature citedCarl, H. 1933: Über die blattbürtigen Brutsprösschen beiPlagiochila. - Ann. Bryol. 6: 15-19.Degenkolbe, W. 1938: Brutorgane bei beblätterten Le-bermoosen. - Ann. Bryol. 10: 43-96.Fulford, M. 1955a: The patterns of development ofsporelings, gemmalings, and regenerants inNowellia curvifolia (Dicks.) Mitt. - Rev. Bryol.Lichénol. 24: 41-48.Fulford, M. 1955b: Sporelings, gemmalings andregenerants in Isopaches bicrenatus (Schmid.)Buch. - Bryologist 58: 317-322.Fulford, M. 1955c: Sporelings, gemmalings and regene-ration in Blepharostoma trichophyllum (L.)Dum. - Mitteil. ThÜring. Bot. Gesellsch. 1:245-258.Fulford, M. 1956: The young stages of the leafy Hepaticae:a résumé. - Phytomorphology 6: 199-235.Inoue, H.  1974: Illustrations of Japanese Hepaticae. I. -i-viii, 189 pp. Tokyo.910Inoue, H. 1984: The genus Plagiochila (Dum.) Dum. inSoutheast Asia. - 142 pp, 76 pls. Tokyo.Inoue, H. 1987: Steereochila, a new genus of the Plagio-chilaceae from the Neotropics. -  Mem. NewYork Bot. Gard. 45: 279-282.Inoue, H. 1988a: Notes on the Plagiochilaceae, XV. Thegenus Steereochila Inoue and Plagiochila eg-gersii, sp. nov. -  Bull. Natn. Sci. Mus. Ser. B(Bot.) 14: 135-141.Inoue, H.  1988b: Concepts of sectional and subgenericlevels in the genus Plagiochila (Hepaticae). -J. Hattori Bot. Lab. 64: 67- 70.Nehira, K. 1968: The germination of gemmae inCalypogeia tosana and Cephalozia otaruensis.- Bull. Biol. Soc. Hiroshima Univ. 34: 1-2.Nehira, K. 1983: Spore germination, protonema deve-lopment and sporeling development. - In:Schuster, R. M. (ed.), New manual of bryology.1: 343-385.Nehira, K. 1987: Germination of gemmae in some mossescollected from North America. - Pap. PlantEcol. Taxon. Mem. Dr. Satoshi Nakanishi.Kobe Geobot. Soc. Sept. 1987: 355-360.Piippo, S. 1989: Bryophyte flora of the Huon Peninsula,Papua New Guinea. XXX. Plagiochilaceae (He-paticae). -  Ann. Bot. Fennici 26: 183-236.Schuster, R. M. 1959: A monograph of the nearcticPlagiochilaceae. I. - Amer. Midl. Nat. 62: 1-166.Schuster, R. M. 1978: Studies on Venezuelan Hepaticae.I. - Phytologia 39: 239-251.Schuster, R. M. 1984: Comparative anatomy and mor-phology of the Hepaticae. - In: Schuster, R. M.(ed.), New manual of bryology. 2: 760-891.

On the asexual reproduction of Plagiochila pluma Steph.

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