Thelypteridaceae

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Thelypteridaceae

Distribution

Europe: present Throughout the tropics, especially in wetter areas: present temperate regions: present
Throughout the tropics, especially in wetter areas; species few in temperate regions (5 in Europe), almost 1000 in all. The majority are terrestrial ferns of forest, but a few (especially in Christella and Macrothelypteris) occur in open places only, and a few (Cyclosorus, Thelypteris) in open swamps; some are adapted to grow on rocks by streams; very few are scandent; a few are casually epiphytic.

Taxonomy

The distinguishing characters of this family were not recognized until Christensen's study of tropical American species in 1913 (see below); in the 19th Century there was much confusion in the use of generic names which were based mainly on soral characters.

Linnaeus placed the species known to him in Polypodium or Acrostichum; he did not use characters of indusia in distinguishing genera. The name Thelypteris was published by Schmidel in 1763; it has been conserved against Thelypteris Adanson (= Pteris) which may have been published earlier in the same year. In 1791 Schreber proposed the name Meniscium for a species from tropical America having elongate exindusiate sori resembling those of the Malesian species here named Pronephrium triphyllum, which was transferred to Meniscium by Swartz in 1801; other authors followed this assignment but Christensen stated his belief that the Malesian and American species in question are not closely related; see further discussion under Pronephrium.

In 1800 Roth published the name Polystichum for ferns with either peltate or reniform indusia; these included some Thelypteridaceae in addition to Polystichum aculeatum (generic type) and species of Dryopteris and Gymnocarpium. Gaudichaud later included some tropical Thelypteridaceae in Polystichum.

In 1801 Swartz published Aspidium, with almost the same diagnosis as Polystichum Roth, and included in it, besides Thelypteridaceae of several genera here recognized, species now placed in Tectaria, Oleandra, Nephrolepis, Didymochlaena, Polystichum, Dryopteris, Cystopteris and Athyrium. Also in 1801 Cavanilles published the name Tectaria with a single species (now recognized as type of a non-Thelypteroid genus) but he later included in it a mixture similar to that in Aspidium Sw. In 1803 Michaux published Nephrodium, which also included species of many genera now regarded as distinct; see below for confused later usage of this name.

In 1824 Bory published the name Lastrea for "la plus grande partie des Polypodes ä feuilles bipinnatifides ou bipinnees", citing a few species only; he did not refer to Aspidium or Nephrodium, though the species he cited could have been placed in either. In 1833 Link published Cyclosorus for the single species which he named C. gongylodes; this had previously been included in Aspidium, Nephrodium and Polystichum. Blume in 1828 included all indusiate Thelypteridaceae in Aspidium, exindusiate ones in Meniscium, Gym- nogramme and Polypodium; he established Stegnogramma for a species with elongate exindusiate sori and anastomosing veins.

Schott's 'Genera Filicum', published in 1834, contained twenty beautifully engraved plates showing details of as many genera; these included a plate illustrating Nephrodium which showed for the first time with great exactness the unicellular acicular hairs charac- teristic of all Thelypteridaceae (also capitate hairs) and other details now considered significant; he also mentioned the vascular strands in the stipe. His description of the genus and list of species shows that he restricted it to thelypteroid ferns having anastomosing veins and round indusiate sori, none of which were in the original list published by Michaux (to which he did not refer). Schott also recognized Thelypteris Schmidel as an allied genus with free veins.

In 1836 appeared Presl's 'Tentamen Pteridographiae', containing a completely new system of fern genera. He adopted Schott's definition of Nephrodium and included most free-veined thelypteroids in Lastrea. But in Lastrea he also placed species of Dryopteris, Ctenitis and several other genera now recognized. He retained exindusiate free-veined Thelypteridaceae in Polypodium sect. Phegopteris (with much admixture of non-thelyp- teroids), those with anastomosing veins of the Nephrodium pattern in Coniopteris and those with elongate sori in Grammitis. In 'Epimeliae Botanicae' (1851) Presl proposed the new genera Haplodictyum, Physematium, Proferea and Pronephrium for thelypteroid ferns from the Philippines and Java.

W. J. Hooker devoted the last twenty years of his life to producing 'Species Filicum' (five volumes, 1844-1864). He united all indusiate Thelypteridaceae in Nephrodium, and with them Dryopteris, Ctenitis and Pleocnemia; he followed Presl in placing exindusiate species in Polypodium, but those with elongate sori in Gymnogramme and Grammitis.

Simultaneously with Hooker's work, A. L. A. Fee produced his 'Genera Filicum' (1852), in which his arrangement is more elaborate. He placed the majority of Thelypteridaceae in Polypodiaceae, tribe Aspidieae. Free-veined indusiate species, mixed with others now allocated to Dryopteris and Ctenitis, are placed in Aspidium; species with anastomosing veins and indusiate sori in Nephrodium, Haplodictyum and Abacopteris; species with round exindusiate sori in tribe Polypodieae, genera Phegopteris and Goniopteris; species with elongate sori in tribe Meniscieae and tribe Leptogrammeae (with admixture of species now referred to very different groups).

G. Mettenius, in his 'Fil. Hort. Bot. Lipsiensis' (1856) included both indusiate and exindusiate thelypteroids with free or anastomosing veins in his "tribe" Aspidiaceae, separating all exindusiate species as Phegopteris, the rest in Aspidium. In his monograph of Phegopteris and Aspidium (1858) he had many non-thelypteroid species in both genera; but in his descriptions he noted characters of hairs, glands and scales with much more care than any previous author except Schott.

John Smith, who observed more than 1000 species of ferns as cultivated plants, published another Classification in 'Historia Filicum' (1875) and in a long introduction commented on previous schemes. He placed almost all thelypteroids in his tribe Phegop- teridiae, separating indusiate and exindusiate species (the former as Lastrea and Nephrodium) in much the same way as Mettenius, but noting that indusia are sometimes very small or fugacious so that separating on this character was often doubtful. Among free- veined ferns named Lastrea he had representatives of other genera (as now recognized) but he subdivided Lastrea to show some of these differences, as Mettenius had not done.

R. H. Beddome, studying ferns in the field in southern India from 1856 to 1882, used Hooker's Classification but recognized some of its unsatisfactory features. In his Handbook (1883) and its Supplement (1892) he included also species of the Malay Peninsula, and owing to a lack of critical study of Malesian ferns he sometimes misidentified Indian species with those of Java.

Field work on ferns in Java was undertaken by M. Raciborski in 1897-1898, and the results were published in 'Flore de Buitenzorg, I, Pteridophytes' (1898). This includes much previously unrecorded ecological Observation. Raciborski placed free-veined Thelypteridaceae in Aspidium (with species of Dryopteris and Ctenitis) and those with anastomosing veins in Nephrodium.

H. Christ in 1897 attempted a new survey of all ferns ('Die Farnkräuter der Erde'). He followed Mettenius in placing almost all thelypteroid ferns in Aspidium and Phegopteris. Subsequently he adopted Christensen's concept of Dryopteris (see below) and in 1907 his survey of Dryopteris in the Philippines was published; his work on the present family was uncritical.

L. Diels compiled a summary of Polypodiaceae for Engler & Prantl's 'Natürlichen Pflanzenfamilien' (). He included all thelypteroid ferns in his tribe Aspidieae, almost all of them in Nephrodium, uniting indusiate and exindusiate species in one genus for the first time. He made an elaborate subdivision of Nephrodium, with free or anastomosing veins as a main distinction (vascular anatomy, scales, hairs and glands had no part in his system) and did not clearly separate thelypteroid ferns from the rest.

Carl Christensen based his 'Index Filicum' (1905) mainly on Diels but (following Otto Kuntze) he adopted the older name Dryopteris Adanson (1763) in place of Nephrodium; under it he had the mixture as before. Van Alderwerelt van Rosen- burgh made a compilation of all recorded taxonomic information on Malesian ferns, with new descriptive data for many species, adopting Christensen's scheme (except that he reverted to Phegopteris for exindusiate thelypteroids); this was published at Bogor in 1908. In subsequent years he published new descriptions of many species, his later observations being more detailed and critical, but in many cases he misapplied older names. C. A. Backer & O. Posthumus, in 'Varenflora voor Java' (1939) also adopted Christensen's comprehensive Dryopteris, without attempting to separate thelypteroid species. Their work includes much new field Observation but their citation of synonymy was often uncritical.

Having completed his Index, Christensen realized that there was much mixture of unrelated species in his Dryopteris and he proceeded to make a detailed study of tropical American species. In the course of this work he distinguished thelypteroid ferns from the rest for the first time (), but he retained all in Dryopteris, placing the thelypteroids in subgenera, because he had not studied the Old World species and could not foresee how to fit them into his scheme. In subsequent years Christensen made many studies of ferns of the Old World, adding to his knowledge, and in 1929-1932 R. C. Ching worked with him, specializing on the ferns of China and India. Ching wrote an important series of papers in the decade 1930-1940, including monographic treatment of Thelypteridaceae in mainland Asia, in the genera Thelypteris, Cyclosorus, Abacopteris and Leptogramma. In 1940 he recognized for the first time a family Thelypteridaceae. I accepted Ching's scheme, with reservations, in my book 'Ferns of Malaya' (1955).

Copeland's work on Philippine ferns began in 1904, soon became extended to cover those of neighbouring regions, and culminated in his 'Genera Filicum' (1947) and 'Fern Flora of the Philippines' (1960). In the main, he accepted Ching's genera, but substituted Lastrea for Thelypteris which he regarded as illegitimate; he did not recognize a family Thelypteridaceae, and separated Thelypteris from Cyclosorus solely on the character of free or anastomosing venation; he regarded Lastrea as closely related to Athyrium.

In 1963 Ching elaborated his scheme of Classification of Thelypteridaceae in mainland Asia, recognizing some new genera. K. Iwatsuki made a detailed study of morphology in the family, mainly in Japan and China, and published a new taxonomic survey in 1964-1965, recognizing the three genera Stegnogramma, Thelypteris (with many subdivisions) and Meniscium.

I began a study of all Old World species of the family in 1967, examining the types of almost all species and the complete collections in several major herbaria. I discovered that Malesian species are far more varied than those of mainland Asia, and I thus had a wider field of study than Ching and Iwatsuki. I devised a new scheme of genera which was published in 1971, and subsequently monographs of all Old World species of the major genera except Sphaerostephanos which is almost entirely Malesian and is here treated fully for the first time.

My first conclusion (at which I had already hinted in my book of 1955 on the ferns of Malaya) was that a division between Thelypteris and Cyclosorus based on free or united veins was not a natural one. I also concluded that the nature and distribution of glands and hairs provided important evidence which had never been well recorded. In such a perspective Thelypteris and Cyclosorus, restricted to their type species and near allies, are small and distinctive groups not closely allied to most of the species associated with them by previous authors. There thus appeared to be two alternatives: to include all species of the family in one genus Thelypteris, or to recognize a number of separate genera. I chose the latter because there is such a great diversity in Malesia that within a single genus, to be intelligible, one would always have to specify a subgeneric or sectional name when citing a species; a specific name alone would not give sufficient information.

In the New World are some other distinctive groups, one of which (Amauropelta) extends across Africa to the Mascarene Islands (), doubtfully to Ceylon and not to Malesia. The New World genus Meniscium is mentioned under the genus Pronephrium in the present work. The species of islands in the Pacific Ocean eastwards from New Guinea (about 100) are almost all common to Malesia or related to Malesian species ().

The result of this long history of confusion is that all names published in the 19th Century have been transferred, by one author or another, to Aspidium, Nephrodium and Dryopteris, in some cases also to Goniopteris, Lastrea, Meniscium or Phegopteris; and in the 20th Century most names have been transferred to Thelypteris or Cyclosorus or both. In view of the preference by some people for a comprehensive genus Thelypteris, I have cited names in that genus if such have been published, and I have tried to avoid the use of new specific epithets where such would have to be changed on transfer to Thelypteris.

Few species were originally described in terms which distinguish them clearly from others, with the result that names were often mis-used or new ones needlessly created. Few collectors understood how to distinguish between species of this family and the need for careful preservation of the base of a frond; much herbarium material is therefore in some measure unsatisfactory and new collections by specialists are still needed. Too many species (my own included) are based on a single collection which may not adequately show possible Variation; but in many other cases repeated collections show a degree of uniformity which confirms their status. It cannot be doubted that the number of species in Malesia is very large, and that probably more remain to be discovered.

Cytology

The first reliable reports on chromosomes were by I. Manton in her book of 1950. Subsequently many reports have been published, as summarized by Löve, Löve and Pichi Sermolli in their Cytotaxonomical Atlas of the Pteridophyta (1977). Haploid numbers range from 27 to 36; several species are tetraploid and of some both diploid and tetraploid forms have been reported, in the wide-ranging species Macrothelypteris torresiana tetraploid and hexaploid. Only a small proportion of species have so far been examined, so that generalizations cannot usefully be made. In all recorded cases species belonging to one genus, as here recognized, have the same chromosome number except that both n = 35 and n = 36 occur in the genus Pseudocyclosorus in India (there is only one Malesian species). Hybridization experiments have only been reported by Manton and her co-workers in the genus Christella q.v. for details.

Citation

Ching - in Acta Phytotax. Sinica. 1963
Ching - in Blumea. 1971
Holttum - in J. Linn. Soc. Bot. 1947: 130
K. Iwats. - in Mem. Coll. Sci. Univ. Kyoto B. 1929
Ching - in Mem. Coll. Sci. Univ. Kyoto B. 1964
Pichi Sermolli - in Webbia. 1970: 709
Ching - in Mem. Coll. Sci. Univ. Kyoto B. 1965