Description from Flora of China
Plants with a regular alternation between larger asexual sporophytes and mostly inconspicuous, sexual gametophytes, mostly free-living but retained within sporocarps of heterosporous ferns or developed mostly within spore walls of heterosporous lycophytes (Iseotaceae and Selaginellaceae). Sporophytes mostly with roots (absent in Psilotaceae), stems, and leaves, and with well-developed vascular strands. Stems mostly rhizomes, protostelic, siphonostelic, solenostelic, or dictyostelic, sometimes polystelic, some with limited secondary thickening, articulate in Equisetaceae. Leaves microphylls: scalelike or linear with a single vascular strand and a single axillary sporangium, or fronds (megaphylls): with branched vascular strands, lamina often divided, often compound, with many sporangia on abaxial surface, margin, or specialized sporophore, forked and subtending a 3-lobed sporangium in Psilotaceae. Sporangia thick- or thin-walled, homosporous or heterosporous, sessile or stalked, rarely enclosed within sporocarps. Spores trilete or monolete. Gametophytes filamentous or thalloid, autotrophic or mycotrophic. Male gametes (antherozoids) bi- or multiflagellate. Female gametophytes (egg cells) borne singly within flask-shaped archegonia (largely adapted from Kramer & Green in Kubitzki, Fam. Gen. Vasc. Pl. 1: 11. 1990).
Pteridophytes are conventionally divided into four major groups, Psilotatae, Lycopodiatae (lycophytes or club mosses), Equisetatae (horse tails), and Filicatae (ferns) (Kramer & Green, loc. cit.), or five major groups when Iseotinae/Iseophytina is also recognized (e.g., Ching, Acta Phytotax. Sin. 16(3): 1-19. 1978). Molecular data shows that the lycophytes (Iseotaceae, Lycopodiaceae, and Selaginellaceae), characterized by microphylls and protostelic or polystelic vascular strands, are sister to all other vascular plants but Psilotatae and Equisetatae, along with the Ophioglossaceae and Marattiaceae, are better regarded as basal relatives of the true ferns (Osmundaceae onwards), forming a monophylletic group, the monilophytes, more closely allied to the spermatophytes, the seed-bearing gymnosperms and angiosperms than to the lycophytes (Pryer et al., Nature 409: 618-622. 2001; Smith et al., loc. cit.).
The delimitation of families of extant pteridophytes had been very controversial in the past but a consensus has been emerging on overall relationships, based largely on molecular data from the chloroplast genome. This has shown that traditional characters, particularly those of venation, sori, and indusia, show many parallelisms and convergences such that related genera were placed in different, polyphyletic or paraphyletic, families. This had already been recognized by some botanists who identified many such anomalous genera and placed them within smaller, more homogenous families. The new molecular data showed that some of these families were nested within other families, rendering some families paraphyletic and thus untenable to some modern systematists. Thus, the decision was taken for the Flora of China to follow the most recent overall account of the pteridophytes at family level, that of Christenhusz et al. (Phytotaxa 19: 7-54. 2011), which is largely based on Smith et al. (loc. cit.). Christenhusz et al. proposed the recognition of 48 families, 38 of which occur within China. At generic level, various genera are recognized for Flora of China based on molecular and/or morphological evidence.
Pteridophytes were dominant land plants during the Carboniferous era and a major source of todays coal and oil. Extant pteridophytes are cosmopolitan but are much better represented in the humid tropics, with only a few families (e.g., Dryopteridaceae) well represented in subtropical and temperate regions and rather few extending into alpine regions (e.g., Woodsiaceae) and more arid regions (most notably Pteridaceae subfam. Cheilanthoideae).
In contrast to the 177 genera and 2,129 species recorded from China, the Flora of North America, covering a similar area, has only 96 genera and 554 species. This illustrates the size and importance of the pteridophyte flora of China, which is much richer than that of other comparable temperate areas and is probably the most species-rich country in the world.
Detailed citations for the corresponding volumes of Flora Reipublicae Popularis Sinicae (FRPS), volumes 2 (1959), 3(1) (1990), 3(2) (1999), 4(1) (1999), 4(2) (1999), 5(1) (2000), 5(2) (2001), 6(1) (1999), 6(2) (2000), and 6(3) (2004), are provided under each family in this volume.
Some 265-300 genera and 10,900-11,100 species recognized worldwide (numbers based largely on Smith et al., Taxon 55: 705-731. 2006): extant pteridophytes are cosmopolitan but are much better represented in the humid tropics, with only a few families (e.g., Dryopteridaceae) well represented in subtropical and temperate regions and rather few extending into alpine regions (e.g., Woodsiaceae) and more arid regions (most notably Pteridaceae subfam. Cheilanthoideae); 177 genera (three endemic, one introduced) and 2,129 species (842 endemic, four introduced) in China.
(Authors: Lin Youxing (林尤兴), Zhang Libing (张丽兵), Zhang Xianchun (张宪春), He Zhaorong (和兆荣), Wang Zhongren (王中仁), Lu Shugang (陆树刚), Wu Sugong (武素功), Xing Fuwu (邢福武), Zhang Gangmin (张钢民), Liao Wenbo (廖文波), Xiang Jianying (向建英), Wang Faguo (王发国), Qi Xinping (齐新萍), Yan Yuehong (严岳鸿), Ding Mingyan (丁明艳), Liu Jiaxi (刘家熙), Dong Shiyong (董仕勇), He Hai (何海), Zhang Qiaoyan (张巧艳), Shannjye Moore (牟善杰), Wu Zhaohong (吴兆洪 Wu Shiew-hung), Li Zhongyang (李中阳), Jin Xiaofeng (金孝锋), Ding Bingyang (丁炳扬), Liu Quanru (刘全儒), Shi Lei (石雷); David S. Barrington, Masahiro Kato, Kunio Iwatsuki, Michael G. Gilbert, Peter H. Hovenkamp, Hans P. Nooteboom, Jefferson Prado, Ronald Viane, Maarten J. M. Christenhusz, George Yatskievych, Atsushi Ebihara, Shunshuke Serizawa, Barbara S. Parris, Tom A. Ranker, Norio Sahashi, Elisabeth A. Hooper, Julie Barcelona, Alexandr Shmakov, Harufumi Nishida, Lin Sujuan (林苏娟), Alan R. Smith, A. Michele Funston, Christopher Haufler, Nicholas J. Turland, Judith Garrison Hanks, John T. Mickel, Yoko Kadokawa, Kathleen M. Pryer, W. Carl Taylor, David M. Johnson, Edward R. Alverson, Jordan S. Metzgar, Shigeo Masuyama)