J Hattori Bot. lab. No. 75: 15- 22 (Feb. 1994) A RE-EVALUATION OF FISSJDENS SUBGENUS PACHYFISSJDENS, WITH A DETAILED DISCUSSION OF FISSIDENS GRANDIFRONS AND F GEIJSKESII 1 2 RONALD A. PURSELL AND BRUCE H. ALLEN ABSTRACT . Subgenus Pachyfissidens, lectotypified by Fissidens grandifrons Brid., is based essen­ tially on plants with stiff leaves and pluristratose laminal cells. It is an unnatural and taxonomically superfluous taxon. Species assigned to this subgenus are placed in subgenus Fissidens section Aloma C. Miill. (Fissidens sedgwickii Broth. & Dix.), section Amblyothallia C. Miill. (Fissidens grandifrons Brid.), section Crispidium C. Miill. (Fissidens strictus Hook. f. & Wits.), and section Fissidens (Fissi­ dens rochensis Broth. and F. ventricosus Lesq.), subgenus Serridium (C. Miill.) lwats. (Fissidens boninensis lwats., F. jaiorum Whitt. & Mill., and F. perdecurrens Besch.), and subgenus Sarawakia (C. Miill.) lwats. (Fissidens geijskesii Florsch.). Pachyfissidens, established as a section of Fissidens Hedw. by Muller (l 848), was rec­ ognized as a subgenus by Kindberg ( 1897) and later accepted at this level by Brotherus ( 1901, 1924) in his widely adopted system of classfication. The taxon is distinguished by its rigid leaves, pluristratose laminal cells, an absence of a central strand in the stem, and estomate capsules. Pachyfissidens is here lectotypified with Fissidens grandifrons Brid., Sp. Muse. I : 170. 1806. (Lectotype. In Nova Anglia habitat, without collector, B). Bruggeman-Nannenga (1974) demonstrated that the pluristratose lamina! cells and lack of a central strand are also found in species that unquestionably belong to subgenus Fissidens. Furthermore, estomate capsules are found in the subgenera Octodiceras (Brid.) Broth. and Sarawakia (C. Miill.) lwats., with both stomate and estomate capsules occuring in some members of the latter subgenus. In Sarawakia the estomate condition was consid­ ered a feature influenced by habitat (Pursell et al. 1988). Nevertheless, despite its lack of any uniquely defining characters, Bruggeman-Nannenga maintained Pachyfissidens as a section in subgenus Fissidens. Recent data derived from SEM studies on the p~ristome (Allen 1980, Bruggeman­ Nannenga & Berendsen 1990) and light-microscope studies on the costa (Bruggeman-Nan­ nenga 1990, Stone 1990) have been shown to be valuable in understanding the infra-gener­ ic relationships of Fissidens. These two features frequently appear coordinated throughout Fissidens and are here used in a re-examinations of Pachyfissidens. Pachyfissidens throughout its history has been a depository for species that share a similar type of habitat, i.e., submersion in rapidly running water. The principal features of this group appear to represent a cluster of convergent characters rather than a suite of coor­ dinated characters indicative of a natural relationship. Nine species of Fissidens are 1 Department of Biology, 208 Mueller Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802- 530 I, U.S.A. 2 Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166-0299, U.S.A. 16 J. Hattori Bot. Lab. No. 75 I 9 9 4 presently placed in Pachyfissidens, i.e., F boninensis Iwats., F geijskesii Florsch., F gran­ difrons Brid., F jaiorum Whitt. & Mill., F rochensis Broth., F perdecurrens Besch., F sedgwickii Broth. & Dix., F strictus Hook. f. and Wils., and F ventricosus Lesq. The pur­ pose of this paper is to discuss these species and their taxonomic positions. Fissidens grandifrons is a widely dispersed aquatic species in the Northern Hemi­ sphere. Although gametophytically specialized for an aquatic habitat, e.g., the long-stalked archegonia (lwatsuki & Suzuki 1982) and thick imbricate leaves, the species has retained a terrestrial sporophyte, i.e., one having a long exserted seta. Such a sporophyte usually has stomata in the capsule. However, we have not been able to demonstrate the presence of stomata in the few sporophytes of F. grandifrons available for study. But, this combination of terrestrial and aquatic sporophytic features is not unique. The same combination of fea­ tures can be found in Dichelyma Myr., a genus in the Fontinalaceae with setae up to 20 mm in length and estomate capsules. The peristome of F. grandifrons has been described as belonging to the taxifolius-type (Bruggeman-Nannenga & Berendsen 1990). This type is commonly found in section Ser­ ridium C. Miill. [=subgenus Serridium (C. Miill.) Iwats.], but it also occurs in section Am­ blyothallia C. Miill. There is, however, no concensus on the peristome types in these two sections. Allen (1980) concluded that species of both sections had the same basic type, i.e. the taxifolius-type. Bruggeman-Nannenga and Berendsen (1990), on the other hand, recog­ nized two basic types of peristomes in these two sections, the taxifolius-type and the sim­ iliretis-type, with the former having three variations. They considered the taxifolius-type characteristic of Serridium while the similiretis-type was found mainly in Amblyothallia. However, these types of peristome were not restricted to one section or the other. To the contrary, some species of Serridium were found to possess a similiretis-type peristome and species of Amblyothallia were found with a taxifolius-type peristome. Recently, Stone (1990), upon examining some Australian species, thought that only one type of peristome was represented in Serridium and Amblyothallia. The lanceolate leaves of F. grandifrons (Fig.1) are usually tightly imbricate and stiff. A recent examinations of specimens from sites throughout the range of the species, however, has revealed that there is considerable variation in leaf thickness and costal structure. Mar­ ginal lamina! cells in the distal part of the leaf can be unistratose (Figs. 2, 3, 8, 12, 14), bis­ tratose (Figs. 6, 10), and even quadristratose (Fig. 5). The interior lamina! cells can be bis­ tratose (Fig. 14), pentastratose (Fig. I 0), hexastratose (Fig. 12) to pluristratose (Fig. 5). Moreover, the subsurface lamina! cells are generally larger than the surface cells. The basic structure of the costa includes three stereid bands in the proximal part of the leaf. A ventral and two lateral stereid bands are evident in Figs. 3, 4, and 13 (the ventral band in this last figure is interrupted) and also in the illustration in lwatsuki and Suzuki (1982, Plate LIII). The ventral band can be reduced to a single file of stereid cells (Figs. 7, 15) or it can be missing (Figs. 9, 11). There are basically two stereid bands in the distal part of the leaf (Figs. 6, 8, 12), although one can be lost (Figs. 10, 14), or both can be eliminated (Fig. 5), in which case the costa consists of more or less homogeneous cells. In both the proximal and distal parts of the leaf the lateral stereid bands may fuse (Figs. 2, 11 ; see also Fig. 45F R. A. PURSELL & B. H. AL LEN: A re-evaluation of Fissidens subg. Pachyjissidens 17 Figs. 1- 5. Fissidens grandifrons Brid. 1. Habit sketch of a leaf. 2, 5. Transverse sec­ tions of distal part of leaf. 3- 5. Transverse sections of proximal part of leaf. [1 - 3 from Pursell, Allen & Magill 10984, PAC; 4-5 from Frye: Moss Exsiccati 25, PAC] 18 J. Hattori Bot. Lab. No. 75 1 9 9 4 0 s~. ?o~ § 9 gO•Oo' • o' · ·~ ~·• •• o :·o~ o ~~a ~0r- 6 15 a8Q'.j 0 JJfm 14 ~D.o~··@ Q ~o o ~ 'J/013 12 Figs. 6-15. Fissidens grandifrons Brid. 6, 8, 10, 12, 14. Transverse sections of distal part of leaf. 7, 9, 11, 13, 15. Transverse sections of proximal part of leaf. [6-7 from Wilson 1909, PAC; 8- 9 from Sharp, Clebsch & Thornburgh 2230, PAC; 10- 11 from Bruggeman­ Nannenga 406, PAC; 12- 13 from Lin 12831 , HIRO; 14- 15 from Higuchi 20162, HIRO] R. A . PURSELL & B. H. A t.,LEN : A re-evaluation of Fissidens subg. Pachyfissidens 19 in Crum & Anderson 1981 ). The type of costa that is found in F grandifrons has been shown (Bruggeman-Nannen­ ga 1990, Stone 1990) to be a unique feature of section Amblyotha/lia. Most species of Fis­ sidens have a costa that has two stereid bands throughout its length, but in Amblyotha/lia there are three stereid bands in the proximal half of the leaf, two lateral and one ventral, separated usually by more than three enlarged cells (we include in this term 'guide cells,' 'deuters,' 'conjunctivae,' and 'conductivae' of authors). Therefore, in view of its costal structure, F grandifrons is hereby transferred to section Amblyotha/lia. Specimens examined. Taiwan. Pingtung Co. : Lai 9850 (NY); Taichung Co.: Lai 8699, c.fr. (NY); Taitung Co.: Lai 9651 (NY), Lin 12831, c.fr. (HIRO). Pakistan. Northwest Frontier Prov.: Haghan Valley, Higuchi 20162, c.fr. (HIRO). France. Hautes-Pyrenees: Bruggeman-Nannenga 406 (PAC). U.S.A. California. Mendocino Co. : Wilson 1909 (PAC). Idaho. Fremont Co. (?):Frye: Moss Exsiccati 25 (PAC). Missouri. St. Frarn;ois Co.: Pursell, Allen & Magi/110984 (PAC). Mexico.: Oax­ aca: Sharp, Clebsch & Thornburgh 2230 (PAC). Fissidens geijskesii is known from only the type collections made in Suriname, north­ ern South America. Its leaves (Fig. 16) are similar in shape, arrangement, and texture to those of F. grandifrons. The costa of F. geijskesii in transverse section, however, reveals two stereid bands throughout its length (Figs. 17, 18), separated distally by two enlarged cells and proximally by three or more enlarged cells. The costa is similar to the bryoides-type (Bruggeman-Nannenga 1990) which is found in all groups of Fissidens except sections Amblyothallia and Crispidium C. Miill., and subgenus Serridium. The sporophyte of F. geijskesii has an immersed estomate capsule and a very short seta (0.4 mm long), a feature found only in the aquatic subgenera Octodiceras and Sarawakia. The peristome of F geijskesii is fragile and missing from the holotype, paratypes, and most isotypes. There is, however, an isotype in LAF in which the peristomes are intact. The teeth are reduced, i.e., undivided or irregularly divided, and are papillose throughout their length.