Studies on Metzgeriales: 1. North American Aneuraceae

Journ. Hattori Bot. Lab. No. 62: 299-329 (June 1987) STUDIES ON METZGERIALES: 1. NORTH AMERICAN ANEURACEAE RUDOLF M. SCHUSTER1 INTRODUCTION During the course of forty years of study of North American Aneuraceae (Ric cardiaceae) it has become evident to me that both Aneura and Riccardia present pro blems not addressed by the extant literature. In this paper I attempt to deal with these problems; for some, only tentative solutions present themselves. Indeed, my purpose is to call attention to some intractable problems whose resolutions may necessitate careful cytological work, growth experiments, and even genetic analysis, if and when we reach such a point in Hepaticology. In any event, the current "pigeon holing" of plants hardly reflects the actual, vastly more complex situation. Several papers directly or indirectly impinge on this study - that of Evans (1938) on capsule-wall anatomy, done with the usual care and precision typical of all of his work, and the study on oil-bodies of British Riccardia species by Little (1968). Prior to publication of this last, very helpful paper, I had drawn and described the oil-bodies of all American taxa and realized that both R. latifrons s. lat. and R. multifida s. lat. were actually species-complexes. That much was readily evident ; what was not evident at all, and what still remains ill-founded today, is how to treat these taxa in a taxonomic sense. Among biologists - but not necessarily among taxonomists, who are bound by a code that insists on a precision the material fails to reflect - it is common knowledge that taxa exist in all shades and manifestations. The current code states that if the ambiguity with regard to the status of a taxon is reflected in the way this is treated, that taxon is invalidly described. Therefore, in this paper, I adhere to this dictum - but, in the discussions, I try to make clear that such a treatment ill serves the complexities of the group. That complexity was already evident from the work of ShowaIter (1926, 1928), who showed that the supposedly "simple" Aneura pinguis consisted of a series of "races" that were, in part, intersterile. Showalter dealt only with material from a limited area of temperate eastern North America and western Europe. What if he had has ac cess to material from, i.a., the Rio Negro of Brazil. the north coast of Ellesmere I. , Campbell I. (situated midway between New Zealand and the Antarctic), and Taiwan? I have studied material from all these areas (and collected it from all but the last) ! Morphologically it all seems virtually inseparable. Of necessity, I cannot deal here with problems of fertility barriers as they impinge I Cryptogamic Laboratory, HadJey, Massachusetts, 01035. Emeritus Professor of Botany, University of Massachusetts, Amherst. 300 Journ. Hattori Bot. Lab. No. 62 1 987 on taxonomy. But these concepts must, marginally at least, impinge on our taxonomic evaluations. Mitigating against these limitations are several facts: (a) I have repeatedly collected each of the taxa treated and am familiar with their ecology and "behavior"; (b) fortunately, starting about 35 years ago, I began to make, and slowly accumulate, detailed notes on the gametophytic anatomy of populations sampled, the capsule-wall anatomy, the spatial relationships of the gametangia, and the presence vs. absence of oil-bodies (and, if present, their numbers and sizes) in both epidermal and hypodermal cells. For all the taxa, detailed drawings were prepared - especially when two species occurred admixed. The bulk of illustrations, formal diagnoses, and details as to dis tribution are all appearing in Vol. V. of my Hepaticae and Anthocerotae of North America (Columbia Univ. Press, 1988). In this paper critical analyses of the more difficult out standing problems and attempts at solutions are presented. The two treatments are intended to complement each other. At the outset, let me emphasize that no future progress is likely to be made with "traditional" methods of study. Herbarium specimens of Riccardia species, even if well prepared, are of limited use as are specimens without sporophytes. And, indeed, dead material - thus without oil-bodies - is often almost worthless. Hopefully the "Nomenklaturfanatiker" (to use the derisory term of Reimers) will keep this in mind and avoid useless name changes based on old (and often poor) herbarium specimens. K EYS TO NORTH AMERICAN TAXA OF RlCCA RDIA For orientation two keys are presented, one with emphasis on cytological features, the other using sexuality as the prime criterion. Key to Living Plants of Riccardia 1. Oil-bodies in epidermal cells 2-4 or even 5- 10 or more, often in central clusters. Bisexual. Often with gemmae. ........ ..... .... .. .. .......... .. .. .. ..... .. ... 2 2. Thallus margins bordered with a unistratose hyaline border 3- 6 cells wide; autoecious; sexual branches from leading axes .. ...... ............ .. .. R. sfricfa 2. Thallus margins tumid, not bordered; synoecious; sexual branches from leading axes or primary branches ... ..... ........ ............ .............. R. jugata 1. Oil-bodies 0 or 1(2) in epidermal cells. ..... .. .... ...... ...... .. ........ ... 3 3. Some epidermal and all (or almost all) hypodermal cells with oil-bodies ... .... .. 4 4 . Oil-bodies absent from at least 5 % of epidermal cells. Ultimate thallus segments with a translucent unistratose wing mostly (2)3-4(5) cells wide . .. .. R. mU/fi/ida. .. 5 5. Autoecious (but ~ and c3 branches sometimes sympodial). Primarily northern in range ... ........ ..... .. .. R. multi/ida subsp. mU/fi/ida 5. Largely or entirely synoecious (occasional su pplementary c3 or ~ branches present). Primarily southern .. .. .... R. mufti/ida subsp. synoica 4 . All (R. pa/mafa, some) epidermal cells with 1 or 2-several oil-bodies. Thallus segments never conspicuously winged [in R. chamedryfolia a 1- 2(3)-cell wide wing occasionally distinct]. Auto- or dioecious . .... .. .... 6 6 . Autoecious. Epidermal cells thin-walled, over 80 % of cells with oil-bodies. Thalli thin, main segments not tumid or rounded on R. M. SCHUSTER: Studies on Metzgeriales, I 301 margins; regularly or irregularly 2-3-pinnate usually, creeping in growth; almost never on decaying wood. Gemmae rare .. .. ...... R. chamedryfolia 6. Dioecious. Epidermal cells thick-walled, under 20 % of cells with oil bodies. Thalli firm, to 8-9 cells high on main axes, opaque, main seg ments tumid or rounded on margins; irregularly pinnate to, distally, su b palmate, mostly with ascending branches; on wood. Gemmae common ... R. pa/mala 3. Neither epidermal nor hypodermal cells with oil-bodies. Autoecious .... .. .. .... R. lalifrons .. 7 7. Main thalli usually under 1 mm wide, soon losing apical dominance, the branching becoming irregular; cross sections never lunate, dorsal surface flat to convex. Xylicolous .......... .. ............ .... R. latifrons subsp. lalifrons 7. Main thalli to ] .5-].8 mm wide, retaining apical dominance, branching 1- 2- pinnate (if 2-pinnate, the secondary pinnae sl ight, very few) but distally merely pinnatifid (pinnae lobelike, reduced, short). Cross sections of main segments often lunate. On peat ... .. ..... ... ......... .... R. lalifrons subsp. arclica Key to Plants with Sex Orga ns 1 . Dioecious; thallus margins opaque, never unistratose for more than 1 cell row; branching irregularly I-pinnate to subpalmate..... .. ........ .... .... .. ..... .. ... ... .. 2 2 . Thallus concave above, channeled; plants slightly, irregularly pinnate; thallus 5, rarely 6 cells thick at middle of main segments, the segments crescentic in cross section, 500- 1000 ft wide; epidermal cells usuall y with 1 oil-body each ........ .. [R. incurvataF 2. Thallus usually biconvex, slightly convex above; plants freely, irregularly palmately branched, dark green, segments only 200--300 ft wide; thallus 7-9 cells thick on main segments; epidermal cells usually without oil-bodies (present in less than 20 % of cells) . .... .. .. .. .. .. .. .... .. ... .. .... .. .. R. pa/mala ] . Monoecious; thallus usually flat or convex above; plants regularly to irregularly 1- 3- pinnately branched. .... .. ..... .. .............. ........ .. ......... ........ 3 3. Ultimate (and usually penultimate) segments of thalli pellucid and unistratose for a width of 2--4 or more cells, on main axes for a width of usually 0)2 cells; plants usually freely 2- 3-pinnately branched; oil-bodies typically 1- 3(4) or more per hypodermal cell, bluish to brownish gray. Capsules with inner cell layer without thickenings (or with them thin and exceedingly vague, not sharply defined); outer layer with nodular thickenings, hardly tangentially extended; often with gemmae. .. ......... ............. ... ..... ... .. .... .. 4 4 . Sexual branches widely spreading, often in sympodial clusters of 2-3 branches, not partially hidden under thallus margins, when solitary usually nearly at right angles to the axis they arise from; sexual branches variable in position, often largely on primary or secondary branches; epidermal cells 25- 35(40) x 50--75(100) ft, each with 1 or rarely 2 large oil-bodies in some cells, others lacking them; ultimate thallus segments not dilated 2 R. incurvata Lindb. has been reported a single time from North America (Tennessee; Sharp 1939). Frye and Cl ark (1937- 47) properly refused to accept the report, the sole collection having been destroy ed. I have seen no material of the species from North America. 302 Journ. Hattori Bot. Lab. No. 62 1 987 at apices .....................

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