Notes on the Higher Level Classification of the Recent Ferns

Sporophytes with roots, stems and spirally arranged leaves (megaphylls). Protostelic, solenostelic or dicty-ostelic, sometimes polycyclic. Some with limited secondary thickening. Sporangia thick- or thin-walled, homosporous or heterosporous, borne on leaves. Gametophytes axial or flat, mycotrophic or autotrophic. Antherozoids multiflagellate.

33 families.

A firm basis for the alignment of the leptosporangiate fern families, which by themselves are becoming increasingly understood and well-defined, is still lacking. In the treatment of the families given below, ideas about their affinités are presented; but as the family sequence is alphabetical, in accordance with the editorial rules for "The Families and Genera of Vascular Plants", rather than being "natural", it is very difficult to glean an overview of supposed family relationships from the present work. I therefore give a résumé of what I think is the present state of knowledge (or, in many cases, ignorance) about family relationships in the leptosporangiates (Fig. 16). As the views expressed below are essentially my own, I have chosen the first person singular for stating them, in contrast to the style adopted elsewhere in the work.

Opinions diverge widely as to the relationships (if any exist) between the two eusporangiate families; see the remarks given with the family treatments of the Ophioglossaceae and Marattiaceae. The leptosporangiates only will therefore be dealt with more at length.

When the artificiality of the Polypodiaceae sensu Christ (1897) and Diels (1899/1900) was recognized -see especially Ching (1940) - various new schemes of classification were proposed for the now greatly increased number of leptosporangiate fern families. In these schemes, attempts were often made at relating the segregates of the former, inclusive Polypodiaceae to each other in various ways, but also, and especially, to various families of the more primitive leptosporangiates from which they were now often supposed to have been derived independently. Important attempts at such a classification were made by Holttum (1949), Nayar (1970), Mickel (1974), Crabbe et al. (1975), Lo-vis (1977), Pichi Sermolli (1977), and Tryon and Tryon (1982); and, on a more regional scale, i.e., not comprising all genera and families of the world, by Ching (1978).

Of these, the system by Crabbe et al. is not a true system of classification, as only a linear sequence is given which of course can only very imperfectly reflect ideas about affinity; it was devised as a sequence of families and genera for the fern herbarium. Pichi Ser-molli's system (and also Nayar's) is based on a philosophy of emphasizing differences rather than similarities, which is alien to the principles of classification and the spirit underlying the present work. He tended

Aspleniaceae

Blechnaceae

Lomariopsidaceae

Davalliaceae

Nephrolepidaceae

Oleandraceae

Dryopteridaceae

Azollaceae Salviniaceae

Thelyptefidaceae

Polypodlaceae Grammitidaceae

Dennstaedtiaceae

Cyatheaceae Metaxyaceae Lophosorfaceae Dicksoniaceae

I Pteridaceae Marsileaceae

Hymenophyllopsidaceae Monachosoraceae

Hymenophyllaceae

Loxomataceae Gleichenlaceae

Dipteridaceae Cheiropleuriaceae

Plagiogyriaceae Osmundaceae affinities very probable affinities possible, not unlikely affinities possible but very uncertain

Fig. 16. Graphic representation of supposed affinities between fern families. Primitive families at the bottom, derived families above. In the right column isolated families or groups of families. Ophioglossaceae and Marattiaceae do not fit into this scheme to retain taxa whose distinctness had long been strongly challenged, like keeping Loxoscaphe apart from As-plenium, Sambirania from Lindsaea, etc. An extreme example is the recognition of an order Negripteridales, based on the monogeneric family Negripteridaceae; other authors like Tryon and Tryon (1982) doubt or deny (R.Tryon, present work) even generic distinctness of Negripteris from Oteilanthes. Thus, it becomes difficult to find a basis for comparison of Pichi Sermolli's system with that of most other authors, including the one adopted here. Lovis' system has very considerable merits but tends to overemphasize a single character complex, the chromosome numbers. Recent findings of divergent numbers in otherwise homogeneous genera have shown that this character, too, must be handled with caution, although it would seem to be of rather fundamental significance. For example, most but not all species of Asplenium are based on x= 36, of Pteris on x=29, etc., but such (few) divergent numbers as there are do not make these genera artificial as some authors (in these cases, not Lovis!) would have it.

The task of finding relationships among the primitive leptosporangiates is particularly difficult. Several of the families have a long geological record and are evidently the last relict representatives of ancient lineages; it may seem downright methodologically incorrect to try and relate them to other extant families when they have become so strongly isolated by a long evolutionary history and drastic extinction among their members and relatives. Families now occupying such isolated positions are Loxomataceae, Matonia-ceae, Dipteridaceae, Cheiropleuriaceae, and Gleiche-niaceae. Except for the first, they are sometimes placed side by side in a primitive alliance, e. g., by Lovis. Except for the obvious relationship between the third and the fourth, I can see little similarity between these families, which in my opinion should not be squeezed into a group of arguable naturalness. The same holds for the Hymenophyllaceae. I cannot see any evidence for placing them near the basis of an alliance "Hymenophyllidae" that further comprises the majority of the "indusiate leptosporangiates", as was done by Pichi Sermolli; and the placement of the Hy-menophyllopsidaceae near them seems altogether fanciful. Like certain other predominantly epiphytic groups, the Hymenophyllaceae are morpho-ecologi-cally so highly specialized that their relationships cannot at present be determined, and the structure of their receptacle is unique.

Further isolated families are Osmundaceae and Pla-giogyriaceae, the former of considerable antiquity. I agree with Holttum (1949) that they may be distantly related, but no other group seems to have its natural place near them.

Another difficult case is represented by the Schi-zaeaceae, also an old family. They are often connected with the (or some) "Gymnogrammoid" ferns (Pterida-ceae); the resemblance of Mohria to Cheilanthes is certainly suggestive but convergence cannot be ruled out. At the present state of our knowledge the affinity seems hypothetical at best. A defendable hypothesis -but no more than that - seems the derivation of the Marsileaceae from Schizaeaceous stock. These heter-osporous ferns are, however, again so strongly specialized that a more definite statement seems hazardous until new evidence turns up. The Salviniales, of course, have nothing to do with the Marsileales, and their ancestry remains quite obscure.

Holttum and Sen (1961) have re-established the relationship between Dicksoniaceae and Cyatheaceae, although most other workers would not unite these two families into one, as they proposed. Lophosoria-ceae and Metaxyaceae are clearly also related, and these four families constitute a natural alliance that might be treated as an order. Dennstaedtiaceae are in my opinion related to Dicksoniaceae, through genera like Calochlaena, and although they are more derived, placement in the same order, or at most a neighbouring one (in view of divergent spore characters and chromosome numbers), would be justified. A circumscription of the Dennstaedtiaceae as proposed by Holttum (1947,1949) is no longer tenable. There does not seem to be any other family among the higher lep-tosporangiate ferns that shows clear affinities with the Dennstaedtiaceae, with the possible exception of the Monachosoraceae whose taxonomic disposition is, however, disputed and obscure.

As pointed out above, the Pteridaceae may be distantly related to the Schizaeaceae, but convincing proof is as yet lacking. More probably related to the former are the Vittariaceae, a genus like Rheopteris (if this is indeed correctly placed in the Vittariaceae) providing a kind of link with the Pteridaceae. The epiphytic habitat has evidently simplified the Vittariaceae so strongly that they are likely to be very different in appearance from any group that may be ancestral.

Holttum has argued repeatedly (1969,1981) that the Thelypteridaceae are an offshoot from a Cyatheoid ancestor. In my opinion anatomical and karyological evidence does not much support such a derivation; in spore characters the two diverge strongly, too. I am still not convinced that there may not be a link between Thelypteridaceae and Athyrioid ferns, but the admittedly not very close similarities may be deceptive.

A fairly closely knit group of higher leptosporan-giate fern families is formed, I think, by the Dryopter-idaceae (sensu lato, including the Athyrioid ferns with Woodsia and the Onocleoid ferns), Oleandraceae, Nephrolepidaceae, Davalliaceae, Lomariopsidaceae, and Blechnaceae. These families are sufficiently close to make it a matter of taste where to draw the exact limits between some of them: Rumohra to be placed in Davalliaceae or Dryopteridaceae? Nephrolepis placed near Oleandra or not? These two included in Davalliaceae or not? Lomariopsidaceae separated from Dryopteridaceae or included as a subfamily? The Blechnaceae stand farther apart, in terms of morphology as well as of karyology. Anatomically, however, they are not very far from the Dryopteridaceae and I think that inclusion in the present group (order, if desired) can be confidently advocated.

Aspleniaceae are in my opinion a rather isolated family (genus), incertae sedis among the higher lepto-sporangiates. I cannot accept (nor even understand) that Mickel (1974) placed the Athyrioids nearer to the Asplenioids than to the Dryopteridoids, and I cannot see how a family Aspleniaceae as delimited by Crabbe et al. can be at all defined. The petiolar anatomy, the structure of the scales, the chromosome number, to name only some more obvious characters, seem to preclude any assumption of close affinity to the Dryopter-idoid alliance; only spore characters provide some positive evidence. Pichi Sermolli believed the Aspleniaceae to be closer to the Thelypteridaceae, but again I fail to understand on what grounds. Asplenium seems to me to be a fairly recent genus, fully in the process of evolution, with a high degree of interfertility between morphologically divergent members. Moreover, at present we do not have any idea which part of Asplenium may be basal ("primitive") which causes difficulty in relating the family to another one. In accepting the isolated position of Asplenium I agree more with Pichi Sermolli than with other authors.

The last major group to be discussed are the Poly-podiaceae/Grammitidaceae. Whereas an affinity between the two was long denied or at least doubted, recent work has provided arguments for regarding them as quite close; inclusion in one family, as advocated by Tryon and Tryon, may even be considered. But where are the roots of this alliance? The Polypodiaceae are usually derived from a primitive, exindusiate lepto-sporangiate group of families (see above). I cannot find sufficient support for such a derivation, and I think epiphytism has so strongly affected the structure of these ferns as to obscure their affinities insofar as they can be traced by currently available methods. Jar-rett (1980) has argued convincingly that the Polypodiaceae and Grammitidaceae cannot be regarded as derivatives of a "primitive exindusiate stock" if indeed there is (or was) such a thing.

Three genera remain that in my opinion cannot at all be satisfactorily accomodated within the framework of leptosporangiate families. Hymenophyllopsis is definitely not related to Hymenophyllaceae but may not be too far away from Dennstaedtiaceae; further evidence, particularly from karyology, is urgently needed. The genus is distinct enough for placement in a family by itself. Monachosorum is less distinct, but the evidence as to affinity from its various characters is so equivocal that it is placed in a family of its own, too, although this constitutes an admission of ignorance rather than of knowledge. Finally, Pleurosoriop-sis is evidently a small, reduced, and much derived genus, but derived from what? This is evidently still quite enigmatic; but the genus lacks distinctive characters that would warrant the erection of a special family for it (which has been done). It is appended below to Pteridaceae, not because of any suspicion of affinity but only because in the general key it will run to that family-

In recognizing a fairly limited number of families in the leptosporangiate ferns, 31 as compared to Pichi Sermolli's 51,1 have tried, with all other authors who have contributed to the present volume, to act in the spirit of the principles outlined above (Kramer and R. Tryon, this Vol.).

References (apart from those included in "General References to Pteridophytes" [p. 14/15]).

Ching, R.C. 1978. The Chinese fern families and genera: systematic arrangement and historical origin. Acta Phyto-tax. Sin. 16:1-37.

Crabbe, J. A, Jermy, A C., Mickel, J. T. 1975. A new generic sequence for the pteridophyte herbarium. Fern Gaz. 11 (2/3): 141-162.

Diels, L 1899/1900. Filicales. In: Engler, A, Prantl, K. (Eds) Die naturlichen Pflanzenfamilien I4. Leipzig. W. Engelmann.

Holttum, R. E. 1947. A revised classification of leptosporan-giate ferns. J. Linn. Soc. Bot. 53: 123-158.

Holttum, R. E. 1949. The classification of ferns. Biol. Rev. 24: 267-296.

Holttum, R. E. 1969. Studies in the family Thelypteridaceae, etc. Blumea 17: 5-32.

Holttum, R.E. 1981. Thelypteridaceae. Flora Maleso. 11.1,5: 331-599.

Holttum, R. E, Sen, U. 1961. Morphology and classification of the tree ferns. Phytomorphology 11: 406-420.

Jarrett, F. M. 1980. Studies in the classification of the lepto-sporangiate ferns: I. The affinities of the Polypodiaceae sensu stricto and the Grammitidaceae. Kew Bull. 34: 825-833.

Mickel, J.T. 1974. Phyletic lines in the modern ferns. Ann. Missouri Bot. Gard. 61:474-482.

Nayar, B. K. 1970. A phylogenetic classification of the ho-mosporous fems. Taxon 19: 229-236.

Pichi Sermolli, R.E.G. 1977. Tentamen Pteridophytorum genera in taxonomicum ordinem redigendi. Webbia 31: 313-512.

Aspleniaceae

Aspleniaceae Frank in Leunis, Syn. Pflanzenkd, ed. 2, 3: 1465 (1877).

Terrestrial, epilithic, or epiphytic ferns of small to medium, rarely to large size; stem short and (sub)erect or sometimes long and creeping, dictyostelic, with well-developed cortical sclerenchyma, bearing non-peltate, clathrate, entire, marginally fimbriate, or glandular, rarely ciliate, dorsally glabrous scales, these sometimes iridescent. Leaves clustered to remote; petiole non-articulate, almost wanting to well-developed, usually smooth when mature, usually with paleae at the base, often hairy and glandular; often dark and sclerotic and then glabrous, adaxially usually flattened to sul-cate, typically with two C-shaped to elliptic vascular bundles back to back joining above the base to near the apex of the petiole to form one X-shaped bundle (Fig. 18 F). Lamina very variable, simple or lobed, more often once or twice pinnate, occasionally more strongly dissected, to quadripinnate (+pinnatifid), anadromous, often truncate at base, thinly membranous to coriaceous, rarely somewhat dimorphic; surface rarely completely glabrous, often with minute uni-seriate (glandular) hairs and slightly scaly; rachis like the petiole but with smaller scales, often also dark-sclerotic; proliferous buds often present on the rachis (on pinnae and sometimes on the petiole), usually borne singly. Pinnae (if any) usually shortly petiolulate to sessile, non-articulate, simple to variously dissected; upper pinnae, pinnules, etc. usually gradually reduced and confluent; a conform terminal pinna only present in some simply pinnate species. Ultimate free divisions of very variable size and shape, usually sessile with rounded to cuneate base, rarely decurrent, never sur-current, sometimes pseudodimidiate or dimidiate, usually costate; edge rarely entire, often crenate-ser-rate, to pinnatifid, the lobes sometimes bifid. Rachises of secondary order (and costae) adaxially grooved, the groove then like that of the primary pinnae, or often convex in the middle, continuous with that on rachises of different order or rarely not; costae adaxially flat to convex or sulcate. Ultimate lobes not rarely narrow and uninerval. Axes scantily scaly, inconspicuously hairy or glandular. Veins anadromous, rarely isodro-mous (sometimes basiscopic veins absent), free and pinnate or forked, rarely sparingly to fully reticulate or loop-connected at their ends; free included veinlets always absent. Vein-ends thickened behind the margin; margin occasionally sclerotic. Sori single, dorsal on the veins, often only on an anterior vein branch but sometimes also on the posterior branch of an adjacent vein-let or alternately on anterior and posterior branches and then approximate in pairs. Indusium attached to the side of the vein, usually long and narrow and with free, tapering ends; occasionally the sori very short and submarginal and the indusium then at its lateral ends often fused with the lamina to form a pouch-like structure ("Loxoscaphe") (Fig. 19 B); when the sori face each other in pairs, the indusia open against each other and the sori are then seemingly confluent at full maturity ("Phyllitis", "Diplora"); rarely the sori following the vein network and here and there back-to-back or branched ("Camptosorus"), or exindusiate and linear ("Ceterach", "Pleurosorus"). Sporangia long-stalked, most of the stalk uniseriate, eglandular; annu-lus vertical, interrupted by the stalk; stomium well-developed, of several elongate cells, passing into the bow, typical of the family. Spores monolete, usually ellipsoid; perispore prominent, consisting of a thin basal layer (inner perispore) pressed against the exospore, this inner perispore bearing rod-like (sometimes forking) structures (middle perispore) sustaining the outer perisporal layer. Middle and outer variously developed, the outer layer often (partly) perforated and/or thrown into variously shaped ridges or into spines.

Rhizomes Creeping Suberect Bearing

Characters of Rare Occurrence. Stem creeping, with many hair-like scales and few paleae, in some very small species like. A. delicatulum C. Presl. Stem with buds in A. prolensum Schräder; petiole base modified into a starch-storage tissue: trophopod (Wagner nnd Johnson 1983), in A. plalyneuron (L.) Oakes, A.adiantum-nigrum L. and relatives. Multiseptate hairs on the leaves in A. pumilum Swartz, A. protensum

Flg. 17A-F. Aspleniaceae, Blechnaceae, and Cyatheaceae, spores (all x 1000). A Asplenium falcinellum. B Asplenium („Loxoscaphe") theciferum. C Woodwardia fimbriata. D Cyathea caracasana. E Cyathea cooperi. F Cyathea (Cnemidaria) horrida. Phot. A. F.Tryon

Exospore Adiantum

Schrader, etc. Amply reticulate veins in, e. g., A. ceter-ach L., A. rhizophyUum L., "Camptosorus sibiricus Rupr.", A. purdieanum Hooker, A. ghiesbreghtii Four-nier, "Diellia laciniata (Hillebr.) Diels", and their relatives; the character occurs here and there in the genus. Some slight dimorphism of sterile and fertile leaves in a few species, e.g., A.platyneuron (L.) Oakes and A. dimorphum Kunze. Abaxially densely scaly leaves in A. aethiopicum (Burm.) Bech^rer, A. ceterach L. and relatives. Indusia of neighbouring son facing each other with their free edges (and often confluent son) in A. scolopendrium L. and other species referred to "PhyUitis", "Antigramma", "Diplora", etc. Partly "double" sori, back-to-back on one vein ("diplazioid") in a few species, e. g., A. melanopus Sodiro.

Indusia facing the margin with their free edges and on veins near and parallel to the margin in "Diellia" (Fig. 18D,E). J-shaped indusia in A. onopteris L., etc. Buds on the prolonged, apically lamina-less rachis in A. mannii Hooker, A. bipinnatifidum Bak., A.fugax Christ, and in some neotropical taxa (A. alatum Humb. and Bonpl. ex Willd., A. radicans L., etc). Linear ultimate divisions in A. septentrionale (L.) Hoffm., A. novae-caledoniae Hooker, etc. Flabellate, ecostate pinnae in some (African) taxa: A. laurentii Bommer ex Christ, A.jaundeense Hieron., A. megalura Hieron. ex Brause. Non-dehiscent sporangia in A. lepidum C. Presl (Brownsey 1977 c). Absence of the outer peri-sporial layer in A. seelosii Leybold.

Fern Transection Rachis

Fig.l8A-I. Aspleniaceae. A,B Asplenium triptewpus. A Pinna with sori ( x 4). B Part of rachis ( x 20). C Asplenium septentrionale, transection of fertile segment (x25). D,E Asplenium („Diellia erecta"). D Fertile pinna ( x 3). E Maigin with son (x8). F Asplenium sp., vascular bundles of petiole, at base (above) and higher (below) (schematic). G Asplenium nidus, sporangium ( x 140). H Asplenium septentrionale, scale of stem (x10). I Asplenium cardiophyllum, scale of stem (x20) (A-C, H from Flora Tsinlingensis 1974; D,E Perez Arbelâez 1928; F from Ogura 1972; G from Haider 1954; I from Kurata and Nakaike 1981).

Morphology and Anatomy. The family as far as investigated is quite homogeneous (Fig. 17). Certain variations are to be found in the rachis structure: concave, sulcate, or the groove with raised middle; adaxially grooved vs. non-grooved or raised costae; reticulate or semi-reticulate vs. free veins; etc. Leaves without lamina that root at the apex and produce new plantlets, formerly misinterpreted as stolons, occur in A. bipinnatifidum Baker and A. mannii Hooker (Fig. 19 A). As in Lindsaea, hardly any morphological or anatomical adaptations to epiphytism can be observed in epiphytic species, except in the so-called nest ferns (Section Thamnopteris Presl) (Holttum 1974) and a few other, unrelated species like A. serration L. and A. africanum Desv. where they are weakly developed.

The stomata are principally polocytic, with stauro-cytic and paracytic ones occasionally present besides.

The most extensive studies of the stem anatomy are by Mitsuta et al. (1980) and by Chandra and Nayar (1975). The rhizome is dictyostelic, radial in species with erect, dorsiventral in most of the (rather few) species with creeping stem, e. g., Sect. Hymenasplenium (Iwatsuki and Kato, 1975); see also Tardieu-Blot (1932).

The leaf trace and petiolar bundle are single in a few small, obviously reduced species.

Laminal parts of about two cell layers with few or without any stomata have been reported for a variety of A. unilaterale Lam. (Iwatsuki 1975).

  1. Little comprehensive work is available; for a review, see Atkinson (1973). The prothallia are of the common cordate or elongate-cordate type; in some species they are naked, in others they bear papillae and/or uni- to multicellular, usually chlorophyl-lous hairs. The few that are known in "satellite genera" are not divergent (Wagner 1951; Atkinson 1973).
  2. Nothing definite is known about the affinity of the Aspleniaceae. Various group have been thought of as potential relatives, like Thelypteridaceae, Blech-naceae, and Athyriaceae, but the similarities are not numerous and may be due to convergence. The former confusion of Asplenium with Diplazium (and Athyr-lum) is well known; for a good summary of differentiating characters, see Smith (1976). Any idea about affinity between Diplazium and Asplenium has now been dropped. However, perispore structures closely similar lo some encountered in Asplenium are found in Thel-ypteris (sect. Stegnogramma) and in Polystichum.

CiiiOGRAPHY and Ecology. The more than 700 species of Asplenium are distributed all over the world, some species even extending into Arctic and arid ureas. The majority are in the (sub)humid tropics and south-temperate regions. Many occur in tropical-mon-lune vegetations. Here they grow on the forest floor, on banks, and in ravines, often on rocks, less often as high epiphytes; a few species are virtually scandent as (licy ascend trees with their rooting-proliferating rachis

Fig. 19A-F. Aspleniaceae. A,B Asplenium („Loxoscaphe") mannii. A Entire plant, with „stolons" (x 0.6). B Fertile segment (x5). C Asplenium rutifolium, fertile segment (x5). D,E Asplenium laurentii. D Habit (x0.3). E Pinna (xl). F Asplenium („Ceterach") cordatum, leaf (x0.6) (A-C,F from Schelpe 1970; D,E from Tardieu-Blot 1964).

tips (e. g., A. sandersonii Hooker). A few species are obligate tree-fern epiphytes (A. hypomelas Kuhn). The concentration of species with proliferous buds in Africa is peculiar. The "nest-fern" epiphytes have been mentioned; they are humus collectors. A very few species are known to be rheophytes (e.g., A. subaquatile Cesati).

Asplenium is a cosmopolitan genus, and one of the very few that is represented about equally in all tropical areas [c. 30% in the neotropics, c. 22% in Africa, c. 33% in Asia, c. 10% in the Pacific (incl. Australia, etc.), c. 5% in Europe s. 1.]. Few species are (sub)cos-mopolitan (e.g., A. adiantum-nigrum L., A. tricho-manes L.). Islands often harbour endemic species, like Madagascar (a 40 species), La Reunion, Hawaii, Juan Fernandez, Tristan da Cunha, the Azores, and New Zealand. Rather few (sub)tropical species occur on more than one continent, e. g., A. monanthes L., A. normale D. Don. Some species have a very restricted distribution (palaeo- or neo-endemics), e. g., A.jahandie-zii (Litard.) Rouy, A. bourgaei Milde, A. balearicum Shivas, etc. Different centres of (secondary) diversification seem to exist, e.g., North America (Appalachians), the mountains of Central America, the Andes, the Himalaya, etc.

Ferns From The Andes

Fig. 19A-F. Aspleniaceae. A,B Asplenium („Loxoscaphe") mannii. A Entire plant, with „stolons" (x 0.6). B Fertile segment (x5). C Asplenium rutifolium, fertile segment (x5). D,E Asplenium laurentii. D Habit (x0.3). E Pinna (xl). F Asplenium („Ceterach") cordatum, leaf (x0.6) (A-C,F from Schelpe 1970; D,E from Tardieu-Blot 1964).

Cytology and Hybridization. Few families are cyto-logically as homogeneous as this. An x number of 36, with diploid to 16-ploid levels based on it (Lovis 1973), has been recorded in all but a handful of species, and in nearly all of the (formerly recognized) "satellite genera"; this, together with the lack of sterility barriers, is veiy important evidence in favour of not recognizing these segregates as genera; (see, e.g., Bir et al. 1985). The exceptions are A. ("Boniniella") cardiophyllum (Hance) Baker: 2n=76; and A. unilaterale Lam., «=40 (Manton and Sledge 1954); a new number of 2/1 — 112, resulting form hybridization of the latter with an m = 36 species (36,,+40,; Bir 1960, 1963), has been recorded in a few populations. The literature on hybridization within Asplenium, often involving "satellite genera", with both naturally occurring and artificially produced hybrids, is enormous; see e.g., Meyer (1952), Wagner (1954), Lovis (1973), Brownsey (1977b), Reichstein (1981), Werth et al. (1985). Half of all known temperate taxa are hybridogenous allopolyploids behaving like species. Intraspecific hybrids are also known. Apogamous taxa (hybridogenous or not) have not been reported in great number; see, e. g., Manton (1950), Manton and Sledge (1954), Mehra and Bir (1960), Braithwaite (1964), Murakami and Iwatsuki (1983). Hybridization and subsequent polyploidy often involve morphologically quite diverse species, resulting in hybrids or species with peculiar intermediate and/or fluctuating morphology; see, e.g., Wagner (1954), Meyer (1965), Walter et al. (1982); also Fig. 19. A single genus:

Asplenium L. Fig. 17-19

Asplenium L. Spec. Plant. 2: 1078 (1753); Maxon (1913); Looser (1944); Sehnem (1963); Sledge (1965); Morton and Lellinger (1966); Brownsey (1977a); Nakaike (1986). Phyllitis Hill (1756). Scolopendrium Adans. (1763). Ceterach Willd. (1804), nom. cons. Camptosoms Link (1833). Antigramma C. Presl (1836). Neottopteris J. Smith (1841). Pteurosorus Fée (1852). Diellia Brackenridge (1854); Wagner (1951). Loxoscaphe Moore (1853). Schaffiteria Fée (1857). Diplora Baker (1873). Asplenidictyum (Hooker) J. Smith (1875). Holodictyum Maxon (1908). Biropteris Ktimmerle (1922). Boniniella Hayata (1927). Hymenasplenium Hayata (1927). Ceterachopsis (J. Smith) Ching (1940). x Asplenophyllilis Alston (1940). x Asplenosorus Wherry 19(37). x Asplenoceterach D. E. Meyer (1957). Sinephropteris Mickel (1976). x Ceterophyllitis Pic. Ser. 1979. x Phytiitopsis Reichstein (1981).

Characters as for family.

C. 720 species, subcosmopolitan; with growing knowledge from biosystematic sources the number of species is likely to increase as species complexes are unravelled. SEM work on spores is also yielding important new data as the genus is very diverse in this respect (see, e. g., Viane 1977).

As to the recognition of natural infrageneric groups, whether subgenera or sections, Asplenium is still extremely poorly known. Some of the "satellite genera" are good candidates for natural sections. Other natural infrageneric groups are sections Thamnopteris and Hymenasplenium, the group of A. aethiopicum (Burm.) Becherer, the A. myriophyllum-abyssinicum group, the A. laetum-erectum group, the A. tricho-manes-monanthes group, etc. Other species groups recognized are often based on superficial resemblance, and may be convenient but are artificial, like "Darea", "Loxoscaphe", etc. The species groups recognized by Mettenius (1859) and Diels (1899) are almost wholly unnatural. The great majority of modern authors have refrained from proposing a natural subdivision of the genus, and we may still be far removed from such a goal. The great majority of the satellite genera are based on single, easily observed characters of little tax-onomic weight. Their source in Asplenium (i. e., their nearest non-deviating relatives) can often be pinpointed.

Selected Bibliography

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