Studies on Marchantiales, I-Iii

Journ. Hattori Bot. Lab. No. 71: 267-287 (Jan. 1992) STUDIES ON MARCHANTIALES, I-III 1 R. M. SCHUSTER I. THE CLASS I FI CATION OF THE G E NUS RICCIA L. Riccia remains a puzzling group whose intrageneric classification is still unresolv ed. Recent chromosome counts (Jovet-Ast 1975; Na-Thalang 1980; Bornefeld 1984) show that in various taxa these range from n = 8, 9, 10 and 12 to n = 16 to n = 24 and 48, with R. caroliniana Na-Thalang, the type of subg. Viridisquamata (Na-Thalang) Jovet-Ast deviant in having n = JO. Subg. Riccia (sect. Riccia sensu Volk & Bornefeld) has chromosome numbers of n = 8, 16, 24 recurring repeatedly, with one [ undescribed] species aneuploid with n = 15, except for R. albosquamata S. Arn., with n = 12. Aside from in the isolated taxa, R. caroliniana and R . albosquamata , thus, chromosome numbers seem to offer little hope for working out an intrageneric phylogeny today. Several taxa (i.a., R. lamellosa s. amplo) occur as polyploid races. If far-reaching attempts at homologizing the basic chromosome complement found in Riccia represent reality, then, eventually, perhaps chromosome structure may give us some aid in refining our classification. To date, it does not. (The attempt by Bornefeld ( 1984) to derive the Riccia genotype, together with that of Takakia and the Antherocotae, from one basic type seems forced to me. We are still not certain if the basic number is 4 or 5 (both are found in Takakia, although Bornefeld states "nur 4 Chromosomen" are found in Takakia; the latter number occurs in anthocerotes). If hepatics and antho cerotes belong to different phyla (Schuster 1977), then attempts at drawing homologies based on their genotypes seem pointless to me. In many respects Riccia, and pre sumably its genotype, are highly derivative.] Although it has been traditional to accept two subgenera (as, e.g., in Muller 1951 - 58, Hassel 1963, Grolle 1976, pp. 248- 49, Volk 1983), Jovet-Ast (1975, 1984) recog nized Thallocarpus and Viridisquamata as additional subgenera. Pteroriccia and Leptoriccia , in addition, were segregated (Schuster 1984, 1985), the first initially at the generic rank but later (Schuster 1985) at the subgeneric rank. Volk and Perold (1986) recently described a monotypic southern African subgenus, Chartacea (with only R. schelpei Volk & Perold). They also recognize a subgenus Spongodes sect. Micantes (Volk & Perold 1986a), with R. hirsuta Volk & Perold as type. This is here regarded as forming an autonomous subgenus. Thus, at the moment, eight subgenera are recognized. I would add here that I am in agreement with Jovet-Ast in recognizing Tha/locarpus ; indeed, in the first stage of MS for Vol. VI of my Hepaticae and 1 Cryptogamic Laboratory, Hadley, Mass. 01035. The research and publication of this work was supported by a grant ( BSR 8709355) from the National Science Foundation. 268 Journ. Hattori Bot. Lab. No. 71 I 9 9 2 Anthocerotae of North America this group was recognized as a subgenus as early as 1953. Volk ( 1983) has drawn a sharp distinction between the two "general" groups currently assigned to Riccia. In the more plesiomorphic group [Ricciella (Spongodes of Volk) and allies] the thallus retains distinct pores and air chambers, and, technically, the dorsal thallus surface is formed of chlorophyllose cells which constitute a true epidermal layer. In the more apomorphic group, thallus development ceases when schizogenous air canals are formed, each typically bounded by four cell rows. In this group (subg. Riccia and allies) we deal, basically, with neotenic organisms: sexual maturity is attained at a time prior to the secondary development of a true epidermis. Instead, the distalmost cells of the cell filaments constitute a more or less ephemeral layer (persistent in taxa such as R. nigrella) which is chloroplast free, at least at maturity. A true epidermis, bearing pores, thus fails to develop. In an ontogenetic sense, the distinctions between the Ricciella- and the Riccia-type thallus are rather profound. I think that, perhaps after careful developmental studies are instituted, it may prove desirable to go back to recognizing these two units as separate genera (Ricciella, Riccia) - each with several subgenera. I remain convinced that Ricciella , in many ways, is more closely allied to Ricciocarpus than to the apomorphic taxa, with mature thallus development curtailed - taxa which then would be referred to a nar rowed genus Riccia. At our present level of knowledge, an eight-subgenus system has many advantages over the "traditional" two-subgenus system most recently adopted by Volk (1983). The principle advantage lies in the fact if a multiple subgenus system is adopted, then each subgenus can be divided into a series of natural complexes, or sections. Volk ( 1983, p. 454) states there are roughly 200 species in Riccia. Of these, more than 65%, or well over 120 species, belong in subg. Riccia, as here adopted. These 120-odd taxa would all fall into sect. Riccia in the Volk classification, while the relatively few taxa of subg. Riccie/la (Spongodes of Volk, after elimination of Tha/locarpus) - perhaps under 30 known taxa - are divided into two sections (Grolle 1976, p. 248) or three (Volk I.e.). In Grolle ( 1976, p. 249) some 39 species of Riccia are cited for Europe - alphabetically, because no sectional classification exists. Similarly, the 19 species of this subgenus known from South Africa (Arnell 1963) are also left in a single, undigested group. It is my contention that organizing a mass of over 120 species without recognition of subgroups is virtually impossible; if comprehension of the group is to be advanced and if the mass of species is to be "digested," we are then almost forced to adopt some method of internal organization. The following attempt, of necessity, remains largely provisional because I have collected Riccia species chiefly in North America and in Europe. 2 With study of Australian taxa and those from Africa, unquestionably other sections will have to be 2 This classification into sections has been in MS for about a decade; it was tested last in 1980-83 (taxa from Texas) and 1984- 85 (taxa from Portugal and Spain). R. M. SCHUSTER: Studies on Marchantiales, I- Ill 269 recognized.3 However, existing diagnoses of many of the African taxa (as, e.g., in S. Arnell 1963) hardly allow a certain placement of these plants. It will become necessary for students residing in these regions, who have access to living material, to test the validity of the sections proposed, and to propose new ones where appropriate. In Vol. VI of The Hepaticae and Anthocerotae of North America the American taxa of Riccia are classified into a number of subgenera (for which see Schuster 1985) and sections; keys to these are given there, obviating a need for including them here. Of the sections, several are new. Latin diagnoses and a brief discussion of each are given here, so as to avoid cluttering up a floristic treatment with such diagnoses. l. Subgenus Ricciella (A. Braun) Reichenb. Synonym. Subg. Spongodes (Nees) Volk, Mitt. Bot. Miinchen 19: 456, Dec. 31 1983. Grolle (1976, p. 248) lectotypified Ricciella with R. fiuitans L. He cites the combination, sub g. Ricciella (A. Br.) Boulay, Muse. France: 164, 198, 1904; this he corrects (Grolle 1983, pp. 406, 426) as follows: subg. Ricciella (A. Br.) Reichenbach, Deutsch. Bot. Herb. (Nomencl.), p. 23, 1841; (Syn. Red.) p. 213, 1841. Volk adopted Spongodes for subg. Ricciella and in Schuster (1985), without independent review, I followed him, although in Schuster ( 1984) Ricciella is recognized as the correct name for this subgenus. With the lectotypification of Ricciella by R. jfuitans, that name, at the subgeneric rank, has clear priority; it has been used by a diversity of authors in a subgeneric sense. Nees ( 1838, pp. 389- 92) gives us the first comprehensive subdivision of Riccia s. amplo, based on earlier observations of Bischoff, recognizing four sections, as follows: Sectio Lichenoides = subg. Riccia in the modern sense " Hemiseuma = Ricciocarpus, in the modern sense 11 Spongodes = subg. Ricciella sect. Spongodes 11 Ricci e 11 a = subg. Riccie/la sect. Ricciel/a Since Ricciella was raised to subgeneric rank by Reichenbach m 1841, it has precedence over subg. Spongodes of Volk ( 1983). Sectio Frostii Schust., sect. n. Thalli valde dimorphi (ef' multo minores quam .'f ), plerumque intensius pigmentosi; cavernulae aeriae angustae et altae, plerumque in primo strato; sporae per superficiem thalli dorsalis liberatae, non areolatae. Type. R. frostii Aust.; perhaps monotypic. Terrestrial plants, the gametophyte strongly heterothallic (d" smaller, often vi naceous); spores emergent from dorsum of thallus; spores small, 40-65 µ, nonareolate, bearing vermiculate ridges. Hassel ( 1963) and Schuster (1991) give treatments of the J Na-Thalang ( 1980) recognized informal groups under sect. Riccia ( = subg. Riccia as treated here), e. g., Group Ciliatae (incL subgroups Longiciliata, Crozalsii), Group Squamatae (incL subgroups Macrospora, Limbata, Sorocarpa) and Group Laevigatae. She similarly divided subg. Ricciella into "Group Terrestriae" (incL subgroups Crystallina, Papulosa, Vesiculosa) and "Group Aquaticae Terrestriae." Not enough data are presented in her memoir to warrant any attempt to correlate the informal (hence nomenclaturally irrelevant) groupings she used with the classification here proposed. 270 Journ. Hattori Bot. Lab. No. 71 I 9 9 2 species; the "intermediate" nature of the thallus anatomy of this species is well known. Sect. Frostii is similar to sect. Ca vernosae but differs in being unisexual and strongly heterothallic; it also is unique in the peculiar spores that lack areolation. Unlike in the Cavernosae s. str., the thallus is relatively compact (cf. Hassel I.e., fig . 85). Sectio Cavernosae Schust., sect. n. Thalli rosulas aut hemirosulas formantes segmentis plus minusve oblongis et epidermide mox lacunosa. Squamae ventrales hyalinae, obscurae, biseriatae maturitate; sporangia per superficiem thalli dorsalis liberata; nullo modo vel infirme heterothallini.

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