Journ. Hattori Bot. Lab. No. 64: 47-57 (Jun.e 1988)

RELATIONSHIPS IN THE ORDER (HEPA TICAE)

H. BISCHLER1

SUMMARY: The order Marchantiales (Hepaticae) contains morphologically well delimited families and genera of which many are monotypic. Its range is world-wide. Present classifications and phylo­ genetic derivations are based mainly upon morphological and morphogenetic homologies that are partly questionable. Recent differentiation is presumed only in two large genera that correspond to two morphologically as weB as ecologicaBy divergent trends in the order. Many other genera are pioneers of xeric, cold, or disrupted, harsh habitats. Morphology and ecology appear linked. The role of ecological adaptation in evolutionary processes is discussed.

The Marchantiales form one of the summits of liverwort evolution (Schuster 1984). They include many pioneers of harsh biotopes, of semi-arid and arid areas, as well as arctic-antarctic, alpine and tropical high mountain regions. Some also readily colonize all kinds of disrupted habitats and became commensals of human activity. Their dis­ tribution is world-wide. Characteristics that may partly explain their high adaptive potentialities include drought or cold resistance, ability to perform assimilation at lower or higher temper­ atures than most other , and dispersal by numerous and resistant spores and, sometimes, gemmae.

THE TYPICAL MARCHANTIALEAN PATTERN A single basic pattern of morphological organization is shared by all Marchantiales and gives the order its consistency. It is characterized by bilaterally symmetrical, thal­ loid with epidermal pores on the upper surface and, in successive layers, aerenchyma, parenchyma, then scales and rhizoids of two types on the ventral surface. Dimorphic cells (oil-cells, slime cells, sclerotic cells and cells with pitted walls) are present in many tissues. Branching is dichotomous, sometimes ventral exogenous or by apical innovations. Anacrogynous gametangia are produced in acropetal sequence. Several of small size develop on each . Sporophytes are radially symmetrical, protected by gametophytic tissue, and consist of a foot, a short seta and a capsule with an unistratose wall containing polar spores and elaters. Growth is assumed by a cuneate apical cell with four cutting faces (Crandall-Stotler 1981). Aerenchyma is developed at thallus apex by internal, schizogenous cell separation. Antheridia are initiated by four androgonial initials. The neck of the archegonia con­ sists basally of six neck cell rows. Spores develop in spherical sporocytes. Spore germina-

1 Laboratoire de Cryptogamie, Museum National d'Histoire Naturelle, 12 rue Buffon, 75005 Paris, . 48 Journ. Hattori Bot. Lab. No. 64 1 988 tion is exogenous, with formation of a germ tube, a germ rhizoid and a protonema reduced to a few cells. Chromosome number is of n = 9 or 8. Polyploid series, up to 4n, exist in 52 % of genera. Constitutive heterochromatin, as far as examined, seems nearly absent in the chromosomes (Bischler 1986; Newton, pers. comm.). Complex flavonoid patterns (Camp bell et al. ] 979) and terpenoids of specific structure (Asakawa at al. ]984) are frequent. Not all enumerated characteristics are consistently found in all families or genera. Structural reorganisations are frequent. However, a majority of the listed features are present in all, including in Monocarpus Carr, placed in the by Grolle (1983). Through its morphological, morphogenetic, cytological, biochemical, physio­ logical and ecological peculiarities, the order appears to be a fairly natural one among the hepatics. However, the Hook., historicaUy included in the order, shows only a minority of the Marchantialean characteristics and is better placed in its own order, as proposed by Schuster (I 963).

COMPOSITION (tab. 1) The order includes 28 genera and about 240 . 19 genera are monotypic or nearly so (in tab. 1 with an *), 5 include less than 10 species, 2 others, 16-20 species. Only two, L. and L., are large. 75 % of these genera were delimited as they are presently before 1874-1881, the date of Leitgeb's morphogenetic studies on the Marchantiales (in bold in tab. I). The genera described later are all monotypic and of limited geographical range. Genera are clear-cut entities that older and recent research in fields other than morphology have not broken down. Sharp morphological discontinuities separate them. Morphological intermediates are unknown. Species attribution to genera is ob­ vious, at least when reproductive structures are present. However, suborders, families and subfamilies are mostly of recent establishment in their present circumscription (in small capitals in tab. 1). Half of the families date from the last 25 years; all of them are monogeneric. This fact does not imply a change in definitions, but an evolution towards more restrictive taxonomic concepts. The order is subdivided into 5 suborders, 14 families and 7 subfamilies. Suprageneric taxa are up to 52 % monogeneric, and further splitting becomes materially difficult. How­ ever, these subdivisions are relevant in so far they translate morphological discontinu­ ities and are not questionable if compared to equivalent taxa of other orders of the Hepaticae. Nevertheless, in such a classification genera are nearly tantamount to supra­ generic subdivisions, and species, to genera.

GEOGRAPHICAL RANGE The monotypic genera are mostly not geographical isolates. Only four of them are narrow endemics (one in South America, one in Australia, two in northern , none in Africa.) In the southern hemisphere (including India because of its relation- H . BISCHLER: Relationships in the Marchantiales 49

TABLE 1. Classification of the Marchantiales (Schuster 1979). *= monotypic taxa; bold = genera delimited before 1881; small capita]s = suprageneric taxa establ ished since 1961.

Family Subfamily Genus No. of Order Suborder spec. Marchan- ·CORSINlINEA E Corsi niaceae *Corsinia 1 tiales *Crouisia 1 *CARRPINEAE *MONOCAR PACEAE * M onocarplIs 1 TARGJO NIINEAE *AI TC HISONJELLACEAE * A itclzisoniella 1 Targioniaceae *Ta rgionioideae 3 * Cy AT HODIOIDEAE Cyathodium 10 Marchan­ "Lunulariaceae * tiineae *WI ESNE RELLACEAE • *CONOCEPHAlACEAE *Conocephaium 2 REBOU UOI DEAE * 10 20 *Cryplomitrium Aytonioideae 16 Athalamia 6 · 2 * Peltolepsis 7 • Stephensoniella Marchantioideae Marchantia 45 * BUCEGlOIDEAE *Bucegia * Neohodgsonisa *DUMORTIEROIDEAE * Dumortieru * MONOSOLENIACEAE * Ricciineae *OXYMITRACEAE * 2 Riccia 100 * ships with Gondwanaland until the beginning of Cenozoic) and in the northern, nearly the same number of genera are present : 24 and 22 respectively, with six genera of only southern, and four of only northern di stribution. Complete holarctic ranges are fre­ quent, indicating di stributions older than the opening of the Atlantic at the beginning of the Cenozoic. In others, speciation took place after that time, e.g. in Plagiochasma Lehm. et Lindenb., with a single widely distributed species, a species complex of three species, each present on a different continent (Baudoin & Bischler 1978), and some narrow endemics or species limited in their range to a single continent. Many other genera were able to extend their ranges in relatively recent periods without undergoing differentiation. They are presently found in regions of recent origin. The number of genera is highest in temperate and India (21), lowest in Australia, New Zealand, tropical Asia and Oceania (8- 9). 50 Journ. Hattori Bot. Lab. No. 64 1 988

Not only genera have wide geographical distributions, but also many species, sometimes broken into disjunct populations. Their ranges are often wider than those known for most phanerogams (Bischler & Jovet-Ast 1986) and may account for out­ standing adaptive potentialities, for instance L. and Riccia sorocarpa Bisch. Endemics are present in both hemisperes, but seem to be more numerous in the southern. About 25 % of species are endemics, mostly Riccia and Marchantia. Marchantialean taxa overwhelm Jungermannialean in arid and semi-arid climatic conditions (50-82%; in temperate: 16 %). Many Marchantiales appear linked to these areas (Bischler & Jovet-Ast 1986).

CLASSIFICA nONS AND PHYLOGENIES Difinitions of genera and suprageneric subdivisions are based mainly on gametangi­ al arrangement and modifications associated with gametangia, as well as on charac­ teristics of sporophytes. The strong tendencies in the Marchantiales to cluster gamet­ angia into receptacles and on more or less dimorphic branches or branch systems, and reduction of sporophytes, stimulated hepaticologists to build up evolutionary trans­ formation series. Due to lack of appropriate data, these are based by necessity on a priori notions of the homology of character states and their "primitive" or "derived" nature. Classifications and phylogenetic derivations thus established rely mainly on the studies of Leitgeb (1874, 1881) who first outlined suprageneric relationships in the order, including morphogenetic as well as morphological data. With few modifications, these are still accepted presently (Lamy 1976). Only the polarity of the series has been seriously questioned. Many presumed homologies have not been reinvestigated since. Recent cytological, ultrastructural and biochemical data are available for a few taxa only and, when interpreted as phylogenetic trends, they often do not outline the same affinities, e.g. similar flavonoid patterns in the morphologically remotely related genera Dumortiera Nees and Wiesnerella Schiffn. (Campbell et al. 1979). The evolutionary significance of homologies, especially when reassessed, cannot be denied, but interpretation of polarity of established series remains uncertain, as out­ lined by Mishler (1986). Morphological mimicry, developmental arrests and structural reorganisations form mosaics of "primitive" and "derived" features in most taxa. Nothing permits me to state if reductions correspond to absence or secondary loss, if specific character states arose only once or several times (for instance reduction of basic chromosome number from 9 to 8, in genera considered morphologically remotely related, as Riccia, Corsinia Raddi, Exormotheca Mitt.), if even striking similarities may be identified as homologies or need reinvestigation, as demonstrated by Crandall­ Stotler (1986). Thus, genera are often treated as "primitive" or "advanced" on an average of characteristics of either category. Accuracy of homologies has been discussed at length during the past century till now. Recently, Schuster (1984) published a thorough revision of past classifications and phylogenies, as well as a summary of comparative anatomy and morphology of H. BISCHLER: Relationships in the Marchantiales 51 the Marchantiales which contains many new data on reassessed homologies. He also proposed a revised list of "primitive" and "derived" features, and a new phylogeny. No new data have come to light since. Therefore, further hypotheses relying on the same background appear untimely.

RECENT DIFFERENTIATION (tab. 2) A look at recent differentiation in the Marchantiales may disclose other relation­ ships among taxa. Two genera only appear likely to have differentiated relatively recently, Riccia and Marchantia. Both are pioneers in their ecological niche and correspond to two morphologically as well as ecologically divergent trends in the order; both contain groups of morphologically closely allied taxa and narrow endemics inhabiting a same area. Such dusters of species are usually considered to be an indication of recent dif­ ferentiation (Zohary 1973). Riccia grows mainly in xeric open biotopes. The species are predominantly mono­ icous, but cross-fertilization should be frequent because their habitats are often flooded. Clusters of nearly allied species are found in the semi-arid and arid continental areas of , South America and Australia. Marchantia species grow mainly in open or disrupted biotopes of temperate re­ gions and tropical high mountain areas. Clusters of closely allied species exist for instance in the mountains of New Guinea and on the Mascarene islands. Recent differentiation appears thus limited in the Marchantiales to predominantly allogamic genera, closely adapted to open and relatively unstable biotopes.

CORRELATIONS BETWEEN MORPHOLOGY AND ECOLOGY (tab. 3) Like Riccia and Marchantia, most other genera of the order are bound to definite

TABLE 2. Characteristics of Riccia and Marchantia.

Riccia Marchantia Biotope xeric open mesic open. disrupted Ecology: light high intensities low intensities temperature high low important changes (up to 50°C) edaphic specialized (pH) tolerant Life cycle short (min. 2-3 weeks) long (min. 3 months) survival after drought growth is restored growth is not restored perennating tubers no tubers Reproduction predominantly monoicous dioicous no asexual asexual by gemmae Morphological trends reductive (gametophyte & elaborative (gametophyte and ) gametophores) spores large, resistant spores small, short-living Species clusters & continental areas of the tropical and southern endemics southern hemisphere temperate islands v. TABLE 3. Correlation between ecology, life strategy and morphological characteristics of genera and families. N

Elaborative Bio- Micro- Reductive trends Genera Families tope topography Habitat Biological characteristics trends life cycle MOllocarpus? M onocarpaceae? scale appendages Cronisia Corsiniaceae shallow basins open predominantly thallus size Corsillia temporary unstable dioicous chromosome number tubers Oxymitra Oxymitraceae river beds restore growth distal spore sporophytes Ricciocarpos Ricciaceae xeric escarpments large spores dehiscence gametangia I arrangement Riccia fI open polyploids Exormotheca Exormothecaceae stable Stephensoniella ..... Plagiochasma Aytoniaceae 0 rock crevices sheltered ,..,c stable monoicous Reboulia ? Targionia Targioniaceae :I:e Dumorfiera Marchantiaceae 8" epidermal pores Neohodgsonia :l. to forests sheltered monoicous aerenchyma complex Wiesnerella Wiesnerellaceae ~ mesic ravines stable life cycle long scale appendages gametophores Aytoniaceae t"" small spores rhizoid dimorphism MOllosolenium Monosoleniaceae '"?" Cyathodium Targioniaceae Z !=' man-made open dioicous complex LUflularia Lunulariaceae a, +>- escarpments unstable gametophores Marchantia Marchantiaceae asexua l reproduction Conocephalaceae Asterella Aytoniaceae arctic cold resistance Manllia cold antarctic stable large spores monoicolls Afhalamia Cleveaceae high mountains polyploids Pe It 0 lepis Sauferia

Preissia Marchantiaceae \0 Bucegia 11 00 00 H. BISCHLER: Relationships in the Marchantiales 53

biotopes. Members of the Marchantiales are terrestrial. Three main ecological factors con­ dition their survival and dispersal: climatic, micro topographic and edaphic (Jovet-Ast et al. 1976). Edaphic conditions act upon species, whereas climatic and micro to­ pographic conditions appear important at generic and suprageneric level. An oversimp­ lified survey of ecological preferences of genera and families and correlations with their life strategy and morphology are given in tab. 3. Xeric biotopes - Open habitats are often temporary. They are easily destroyed by water or wind. Moisture is available for a short time. Only species with short life cy­ cles can survive. Colonizers are characterized by small, Riccia-like thalli. Basic chro­ mosome numbers of n= 8, and spores dehiscing distally at germination exist only in this group. The two morphologically distinct subgroups may also have ecological particula­ rities that are not yet sufficiently documented. In the first, Corsiniaceae Engl., Oxy­ mitraceae K. MUll., Ricciaceae Reichenb., and probably the edaphically highly spe­ cialized Monocarpaceae Carr, archegonia are embedded in thallus tissue, sometimes clustered, sometimes scattered along thallus midrib. Sporophytes are often highly simplified and lack foot and seta and, sometimes, a capsule wall. Elaters are vestigial or absent, and capsules are cleistocarpous. Some Riccia species radiated into mesic or cold, open habitats, while others, together with Ricciocarpos, colonized temporary water ponds. The second subgroup, Exormothecaceae K. Mull., is characterized by shortly stalked archegoniophores. In sheltered habitats, moisture is present for enough time to insure a normal life cycle with seasonal sporophyte development. Colonizers are characterized by relatively large thalli, antheridia grouped in more or less well delimited, sessile receptacles, and shortly stalked archegoniophores (except Targionia). Reboulia and Targionia radiated into mesic sheltered habitats. Mesic biotopes - Colonizers are characterized by antheridia grouped in well delimited, sessile or stalked receptacles, and archegonia on terminal branch systems (except Cyathodium Kunze). In sheltered, stable habitats, moisture is available nearly permanently and allows development of complex archegoniophores. It has been demon­ strated that pores and aerenchyma hinder photosynthesis in very humid and shaded sites (Green & Snelgar 1982), a fact perhaps related to the reductive trends noticed in genera inhabiting such biotopes, e.g. Dumortiera. Cyathodium and Monosolenium sometimes radiate into disrupted habitats. Geological and climatic alterations and human activity created many open, ruderal or disrupted habitats that are colonized by two pioneer genera: Marchantia and Lun­ ularia Adans. (in Asia also Conocephalum supradecompositum (Lindb.) Steph.). March­ antia has reached the highest morphological complexity. Two of its species, M archantia polymorpha and M. berteroana Lehm. et Lindenb., radiated into the Arctic and the Antarctic. Cold biotopes - In these, archegonia develop in mostly terminal but shortly stalked 54 Journ. Hattori Bot. Lab. No. 64 198 8

receptacles that do not reach the complexity in branching and protective devices of those found in mesic biotopes where the season suitable for growth is longer. A few species of Mannia (e.g. M. androgyna (L.) Evans) and Athalamia (e.g. A. spathysii (Lindenb.) Hatt.) radiated into xeric sheltered habitats. To sum up, the morphologically typical Marchantialean pattern is best realized in taxa of the stable habitats of cold and of xeric biotopes. Reductive trends in the gameto­ phyte are noticed in those inhabiting mesic sheltered sites; in those colonizing xeric open, unstable habitats, gametophytes as well as sporophytes appear reduced. Elabora­ tive trends, especially towards a greater complexity of gametophore structure, are pre­ sent in those of mesic biotopes. Asexual means of reproduction exist mainly in those of mesic open, disrupted habitats. Polyploids and large spores are frequent in species of harsh biotopes, whether xeric or cold. Dioicy is predominant in those of open xeric, or mesic disrupted habitats, and revival after drought characterizes those of xeric environments. Morphological and ecological trends are parallel at family level in eleven families. In three, adaptation to different biotopes is noted (in bold in tab. 3): Targioniaceae Dum. to sheltered, mesic and xeric; Marchantiaceae (Bisch.) Lindley to mesic or cold, sheltered or open; Aytoniaceae Cavers to sheltered, xeric, mesic or cold.

ECOLOGICAL ADAPTATION AND EVOLUTION Morphology and ecology appear linked. Many correlations exist at generic as well as at suprageneric level. Did ecological adaptation play a role in evolutionary processes? Beginning of differentiation has to be searched for at the level of populations. Marchantialean populations are usually small, discontinuous in space, often also in time. Suitable and available terrestrial microhabitats are infrequent. Gene flow, that is, sperm, spore and gemmae dispersal distances are short (Wyatt & Anderson 1984). Microhabitats form mosaics of reproductively nearly isolated populations. Outcrossing among near relatives, self-fertilization in the many monoicous species, and asexual reproduction render populations clonal or nealy so. Genotypic coadapta­ tion is thus enhanced. This strong coadaptation may allow for morphological stability and low evolution rates. Surprisingly, meiosis is preserved even in those supposed autogamic species where it does not result in any genetic mixing, male and female gametes being genetically identical in haploids. The role of meiosis seems to be limited in these to elimination of accidents and mutations. In spite of small size and reproductive isolation, populations have been shown to be genetically variable and to differ in allele frequencies (Szweykowski & Krzakowa 1979). The existence of this variability has led to the supposition that interpopulational exchanges have to be more frequent than expected. Species result in heterogeneous populations, genetically variable. Heterogeneity is manifold. It is expressed by morphological polymorphism, e.g. in the dioicous Marchantia polymorpha. However, morphological polymorphism is nearly absent in H. BISCHLER: Relationships in the Marchantiales 55 others, dioicous as well as monoicous, e.g. in Marchantia paleacea Bertol. (Bischler 1986a) or in Riccia sorocarpa Bisch. (Jovet-Ast, pers. comm.). Edaphic adaptation to definite conditions, e.g. to gamma radiation (Sarosiek et al. 1968), to lead containing substrates (Briggs 1972), or to heavy metal pollution (Warncke 1968) has been recorded for Marchantia polymorpha. Different flavonoid patterns (CampbeU et al. 1979), or different aromatic compounds (Asakawa et al. 1984), were found respectively in Marchantia foliacea Mitt. and M. polymorpha. Polyploids of 2n to 4n, mostly mor­ phologically indistinct (Baudoin & Bischler 1978), exist in a number of species. In spite of this diversification, genetic variability and reproductive isolation, most populations show no morphological differentiation, and species remain morphological­ ly well characterized over their whole geographical range (Bischler 1986a). In regions where phanerogamic speciation was particularly active, as in SW Asia, open for coloni­ zation in the second half of the Cenozoic, the Marchantialean species readily spread but did not differentiate (Bischler & Jovet-Ast 1986). In a classical interpretation, genetic variability can not be stored in haploids and should be absent in autogamic populations, but the frequency of autogamy and its incidence in populations are unknown in the Marchantiales. Potentialities for diversifi­ cation exist only in alIogamic populations. Differentiation is not expected to occur frequently through hybridation, not a single hybrid being known presently. Genetic variability could have been maintained in allogamic species by close adaptation to local microhabitats in which selective advantages vary over short distances (Cummings & Wyatt 1981). In open, unstable biotopes, as those typical for Riccia and Marchantia, strong selection could have destabilized coadaptation of genotypes and allowed dif­ ferentiation. Ecological adaptation would then play a role in evolutionary processes. Another interpretation admits storage of genetic variability in haploids. Recently, genetic polymorphism has been demonstrated in haploid autogamic populations of cultivated higher plants (Demarly 1985, 1986). The presence of silent alleles is supposed. Selection of expressed alleles would rely upon the epigenetic system that harmonizes development with environment, and performs ecological adaptation. If a similar re­ gulation occurs in hepatics, it could explain the maintenance of genetic variability, the high ecological adaptive potentialities even in autogamic populations, the morphologi­ cal polymorphism, and the absence of morphological differentiation, unless the highly destabilizing effects of open, unstable habitats can break down this epigenetic regula­ tion. Ecological adaptation would then lack any evolutionary significance.

CONCLUSIONS Morphology, the main foundation of present classifications and phylogenies, de­ pends on complex interactions of genetic, epigenetic, physiological and ecological factors. Phylogenetic derivations may not be as linear as supposed. Reversal of mor­ phological trends as well as similar features turning up several times could exist. Cor­ relations between morphology and ecology outiline relationships among taxa that often parallel those of present classifications. However, whether or not ecological adap- 56 Journ. Hattori Bot. Lab. No. 64 198 8 tation is involved in evolutionary processes depends on whether or not genetic poly­ morphism is stored by the "haploid" Marchantiales.

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